Ashly DPX-100 Stereo Equalizer User Manual
Contents
1. 25 40 63 100 180 250 400 630 1K 1 8K 2 5K 4K 16K 6 3K 10K Gain eo 1 15 6 10 4 am 6dB ASEBLY 4 4 L 4 4 4 4d H amp hH amp u H h 474H 7 4 mL 15dB Model DPX400 ef ee Ome 3 me O Graphic Equalizer 5 3 HPF EQ Compressor Limiter ey 7 9 Sig Clip c c 15 00 1 OO 20Hz dB Out Out 4 MECHANICAL INSTALLATION The DPX 100 mounts in a standard 19 inch equipment rack The mounting screw threads vary with different rack manufactures and you should refer to your rack instructions for proper hardware An oval head or flat head screw with a plastic countersink washer is pre ferred to protect the finish of the DPX 100 under the screw This unit is housed in a rugged steel case and will tolerate moderate abuse However for road systems which may be dropped or otherwise subjected to extreme forces we recommend some rear support for the chassis to prevent bending the front panel the front panel when these forces occur2. LI ATPT2S 12006 2793151 lt E sw2B SW2A BALANCED ROD 12025 4SP2600 OUT 45P2600 OUT 4 lt 4 INPUT C Ashly Audio Inc FILTERS PWR SUPPLY METERS REVISION HISTORY HP noe noT A S IH 007 FILTERS s s 20E 120 2 v 1051551 2 5 1051551c 3 5CH 101551RV SCH 5 5 Webster NY 14580 9103 S To EVEN 5 PEAK BUS 1 FILTER BOARD mmmm P50n6 716 872 0010 Fax 716 872 0739 TO ODD E ALONG WITH SHEET 2 gt Size Sheet 1 4 pos By Print Date 11 44 50 Rev 120B 12028 1 157 james Franks gt gt 56 4560 EVEN 226 T2 INPUT METER lt PEAK BUS2 2 lt lt 2 Ceescus 31 ODD 5 1105 155121 3 2002 gt gt OUTPUT METER METER Vv DPX 100 MINI EQ COMPRESSOR LIMITER APPROVED Dwg 1 0S1 551 1 2 3 4 5 5 7 8 1 40 4 21 onpdvax 001 8 SI AIHSV c2 TO ODD Olu R72 R77 R78 160 Hz R82 R83 KHz R87 R88 6 3 KHz 2925 2 21292 1933 2 22372 C26 TO EVEN lu T2 gt VRI3 c28 4 4 Olu
3. T2 VRI7 C30 TO EVEN 4 Olu EVEN Olu ROS R92 c27 EJ Olu R96 R97 R102 Cal EJ Olu R106 138k R107 JP30 2 JP34 2 ODD ODD lu 13 C36 Olu Ca EJ 1 RILI 255K R112 c35 LJ Olu 8116 392K RIIT TY RI23 25KHz C39 JP27 2 JP35 2 JP39 2 VRIS T TO EVEN ca Olu R135 1 VRI2 JP28 2 3 VRI6 JP32 2 R137 2 gt JP36 2 D R143 4 KHz lt TO EVEN lt Toopp en im 13 gt Ashly Audio Inc 847 Holt Road Webster NY 14580 9103 Phone 716 872 0010 Fax 716 872 07 39 Size shet 2 of 4 Drawn By Print Date 11 43 56 A gt B 157 James B Franks B S Engineering CLIENT98 1551 10s1551c 2 SCH 3 May 2002 lev DPX 100 MINI EQ COMPRESSOR LIMITER APPROVED 5 1051551 7 8 42ajmurT 40ss24dui0 sazyonby advt 001 8
4. 7 3 Chain The chain button on the back panel allows the output of the equalizer to be fed directly to the input of the compressor limiter with no external cable required When the chain switch is in the input connectors to the compressor limiter are removed from the circuit while the graphic equalizer outputs remain functional 7 4 Detector Loop Ducking The DPX 100 compressor limiter has a TRS In sert DETECTOR PATCH point which can be used as a ducking input or in conjunction with an equalizer to produce frequency sensitive limiting Various uses of the detector patch are discussed under TYPICAL APPLICA TIONS 8 TYPICAL APPLICATIONS By itself the 15 band graphic EQ is useful for general tone control feedback control and room reso nance correction The compressor limiter provides many solutions where dynamic signal level processing is re quired The combination of graphic EQ and compressor limiter allows for additional applications such as a full range speaker processor 70 volt distributed system pro cessor mixing console channel insert and frequency sen sitive limiting to name a few In most cases the DPX 100 should be the last device before the power amp or cross over or right before a recording device or transmitter 8 1 GRAPHIC EQUALIZER APPLICATIONS General Tone Control The graphic equalizer is a very useful device for general tone shaping because it is intuitive and easy to adjust The vi
5. 6I 1 2 3 4 5 7 8 E GAIN REDUCTION db D38 D37 036 035 D34 D33 032 030 029 EA AA PA PA PA AA AP 18 046 Dis D40 2169 cns 1548 1208 AR AA AR AA AR AA PY 7 239 20 R 7 1 0 n7 PEAK BUS 1 posee tenes 161 RUN 21 60 Q3 1 5K METER SELECT 689988885 gt E Did INPUT METER 144148 09 8 M3914 a 244123 a 1378 545 2600 R147 150 160 OUT Ex SWIB LSK 100K 452600 52 5 048 8
6. REC ad SEE 5 6 Signal Present and Clip LEDs 6 COMPRESSOR LIMITER CONTROLS 6 1 ga cise Chea CORA PEER Shaw Fea er Fewer dee Py Wed 6 2 Threshold ote eI C ee ed ede Red uude qd 023 cT GA Attack Time eda x nee weak haw aaa Pend CR E 6 5 Release Time ee e E TROU Ur Ue Eg 6 6 Output Level eee beth sedeo 6 7 In Out Switch 6 8 Threshold Gain Reduction Display 6 9 Input Output Meter Display 7 CONNECTIONS AND CABLES 7 1 Balanced vs Unbalanced Connections 7 2 Inputs and Outputs 1235 Chain PR 7 4 Compressor Limiter Detector Loop Ducking 8 TYPICAL APPLICATIONS 8 1 Graphic Equalizer Applications 8 2 Compressor Limiter Applications 5 3 Sp cial EH CtS pred exo sake sae 9 DESIGN THEORY
7. 10 BLOCK DIAGRAM 11 TROUBLESHOOTING TIPS 12 WARRANTY INFORMATION 13 SPECIFICATIONS steeds ee wees 14 DIMENSIONS cde str mee week 15 SCHEMATICS Operating Manual DPX 100 Graphic Equalizer Compressor Limiter The lightning flash with arrowhead symbol within an equilateral triangle is intended to alert the user to the presence of uninsulated dangerous voltage within the product s enclosure that may be of sufficient magnitude to constitute a risk of electric shock to persons CAUTION RISK OF ELECTRIC SHOCK DO NOT OPEN TO REDUCE THE RISK OF ELECTRIC SHOCK DO RE MOVE COVER NO USER SERVICEABLE PARTS INSIDE REFER SERVICING TO QUALIFIED SERVICE PERSONNEL The exclamation point within an eqilateral triangle is intended to alert the user to the presence of important operating and maintenance instructions in the literature accompanying the device TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK DO NOT EXPOSE THIS APPIIANCE TO RAIN OR MOISTURE TO REDUCE THE RISK OF FIRE REPLACE ONLY WITH SAME TYPE FUSE REFER REPLACEMENT TO QUALIFIED SERVICE PERSONNEL WARNING THIS APPARATUS MUST BE EARTHED 1 INTRODUCTION The Ashly DPX 100 combines a 15 band graphic equalizer and full function peak compressor limiter
8. Output 3 Ei 7 2 Inputs and Outputs The DPX 100 uses two different audio connec tor types 1 4 TRS tip ring sleeve phone jacks and three pin XLR connectors will allow interfacing to most professional audio products Ashly TRS balanced con nections use the tip as and the ring as signal with sleeve used for ground Ashly XLR connectors use pin 2 and pin 3 with pin 1 ground Inputs are 20KQ active balanced using precision 1 metal film resistors outputs are 200Q pseudo balanced which means they have balanced impedance with a single ended signal source and can be wired balanced or unbalanced When possible we recommend balanced connections between all components in your system If inputs are used unbalanced the signal should be on the connection and the connection must be tied to ground or signal loss will result While a mono phone plug used as an unbalanced connection will auto matically ground the ring of the jack XLR s will not automatically do this so attention must be given to proper wiring Tip Ring J Sleeve Gnd Stereo Phone Plug used for balanced Tip Sleeve Gnd Mono Phone Plug used for unbalanced XLR Male XLR pins are OIA numbered the 9 RRQ connector 0050505060504 insert 2 3 0 amp TD 1 gnd XLR Female Audio Connector Types
9. QIM INPUT METER gt OK M INK LIMIT 2 418 i ATTACK R33 o RIS 15K IK THRESHOLD 10K 20db MIN 41 4db MAX R22 499K swe GAIN METER gt R28 AOK R32 5 IK 122 Da 52560 244125 1 OUTPUT us n 16 1008 VRA lt PEAK BUS 1 gt R37 DK 144148 TIPSIST Jd 4721050 ELI OUTPUT METER n RATIO SYMMETRY p 25 RS 27 ADJUST vrs 100K ps3 W 144148 gt _ pi wm COMPRESSOR LIMITER OUTPUT BALANCED 17 0db MAX INPUT 3 45P2000 IN CASCADE pu 47U 4 SW8A i EQ SWITCH iN 45 2600 2 4 L 3 2 EQ GAIN 4 JPI9 JP19 2 1P20 JP20 2 2206 lt 5 R57 D7 R50 vns lt gt OUT 390K PEAK BUS 2 b lt 144148 iq diw Eo 6 Dio A 320A R39 s IP17 54 AN o nona v 5 D RSI 3 3 470 20K 10 ps9 4560 R56 22M ams 0 D amp 20K INAIE 19 100K R63 27 RAL 20 Hz HPF 18dB PEAK BUS FLTR gt 9 RANGE SWITCH IN 6dB OUT 15 dB PEAK BUS FLTR gt 10 0K 27 SOLLVINHHOS ST
10. sstart TE 8 5 GAIN METER gt TT lt 18 Joo 226 T n B49 WLIMITER G 18 TC H8 VW R162 ERD Iz 47K E TIAE SDN Y POWER Y mar 1N964 4 Drac V 38 18 R165 Q4 PEAKBUS1 LSK N4125 PEAKBUS2 gt FORIC 5 THRES gt m 2N4125 Quo CLIP R 5 L_ sia gt 2N4123 419 dBu GAIN METER gt Yos Qu 51000 gt 24123 dfi h R174 OUTPUT D52 1N4003 NT 1 in out ula 271 SL ME 1818 49 C53 P T D 1 al 25 1U 1U 547 184003 144003 1N4003 no swo isk 10 D2 22 T T 8 21 mes Ashly Audio Inc 2 tS cas S LY 847 Holt Road 47 1413 INVAC 220VAC 8 4 7918 1N4003 1U 1U Webster NY 14580 9103 n n2 5 2 3 z KEYSTONE KEYSTONI KEYSTONE 51 7308 In Out T Phone 716 872 0010 Fax 716 872 0739 1U 100V Sze shet 3 4 Drawn By Print Date 11 42 28 Rev ns n7 18 19 ERA m B gt 157 James Franks KEYSTONE KEYSTONE KEYSTONE KEYSTONE KEYSTONE N4003 SiEngineering CLIENT98 1551 10s185163 5CH 3 May 2002 Ep ET 9 9 DPX 100 MINI EQ COMPRESSOR LIMITER 77 APPROVED 29 1091551 1 2 3 4 6 7 8 42aynurT 40ss24duio sazyonby 2 001 8uia2d Operating Manual DPX 100
11. Attack Time 20055 20115 Release Time 100mS 3Sec OWtputz iul RES to 18dB Maximum Input Level 23dBu Maximum Output Level 23dBu Input Impedance Output Impedance Frequency Response Distortion Output and Noise 20KQ balanced 2000 Pseudo Balanced 0 2dB 20Hz 20KHz lt 01 THD 04 1KHz lt 0 15 THD 15dBu 20Hz 20KHz lt 95dBu DPX 100 Power Requirements 93VAC 120VAC 50 60Hz 10W Size and Shipping Weight 19 L x 1 75 H x 6 D 8 lbs Note OdBu 0 775 Vrms Pseudo Balanced Output has balanced output impedance with single ended signal ASHLY I3 Operating Manual DPX 100 Graphic Equalizer Compressor Limiter 14 DIMENSIONS OOOO Dimensional Drawing for 100 16 ASHLY TIP INPUT DETECTOR RING SEND BI00K PEAK BUS 1 gt GAIN 1545 RH 3 C66 EI EASE 68 19 RELEASE MM INAL4S 2 100K
12. is easily set and is very stable In designing a graphic equalizer a selection of filter sharpness must be made More sharpness higher Q produces less filter overlap and tighter control over an individual band but also causes ripple in the frequency response when many filters are boost or cut together to produce a flat response We feel that the graphic equalizer s primary use is for voicing and tone control and have set our filter sharpness to produce a maximum of 1dB ripple The summing system in a graphic equalizer is also important Since there are a number of filters which combine to produce the overall response it is important that the filters not interact they WILL overlap but the response of one filter should not modify the response of another Ashly uses an interleaved summing system where every other filter uses the same summing amplifier so that adjacent filters never share the same drive and feedback signals This allows the filters to maintain their natural response Compressor Limiters The Need For Gain Control The human ear excels in its ability to detect an extremely wide range of loudness levels from the quiet est whisper to roar of a jumbo jet When we attempt to reproduce this dynamic range by means of amplifiers tape recorders CD players or radio transmitters we run into one of the fundamental limitations of these electronic media limited dynamic range Amplifier dynamic range is quite
13. nectors and cables with broken strands of wire are very common problems Use quality cables with quality cor rectly wired connectors 11 1 Compressor Limiter Troubleshooting Tips No Output Check AC power Is the power switch on Check input and output connections are they reversed Are you sure you have an input signal Controls Have No Effect Is the limiter in out switch in Perhaps the ratio control is set too low to produce an audible effect or the input level is below threshold Is the threshold LED light ing up If not lower the threshold setting or increase the gain Do not expect to hear any effect when the input level is below threshold since the unit is simply a linear amplifier at those levels ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter When Using Heavy Compression Background Noise Is Noticeable During Quiet Sections Of The Program As defined in the section on compression quiet program material is effectively made louder while loud peaks are made quieter When the program source is thus raised in volume its noise floor is also raised in volume by a proportionate amount This is not a defect in the compressor limiter but an unavoidable side effect of the gain altering process If the noise becomes a problem the solutions are to either decrease noise at the program source or use less compression Excessive Hum Or Noise Hum is often caused by a ground loop between comp
14. After unpacking please inspect for any physical damage Save the ship ping carton and all packing materials as they were care fully designed to reduce to minimum the possibility of transportation damage should the unit again require pack ing and shipping In the event that damage has occurred immediately notify your dealer so that a written claim to cover the damages can be initiated The right to any claim against a public carrier can be forfeited if the carrier is not notified promptly and if the shipping carton and packing materials are not avail able for inspection by the carrier Save all packing mate rials until the claim has been settled 3 AC POWER REQUIREMENTS A standard IEC 320 AC inlet is provided on the rear panel to accept the detachable power cord shipped with the unit Units distributed within the United States are preselected for 120VAC 60Hz and should be plugged into a standard NEMA 5 15 3 wire grounded AC recep tacle Most units distributed outside the US are preselected and labeled for 240VAC 50 60Hz and are shipped with the appropriate power cord The DPX 100 will perform normally from 95 to 125 volts AC An internal line fuse is used In the event of fuse failure refer to a qualified service technician for servicing Power consumption is less than 20 watts ASHLY 3 Operating Manual 100 Graphic Equalizer Compressor Limiter
15. Graphic Equalizer Compressor Limiter ASHLY ASHLY AUDIO INC 847 Holt Road Webster 14580 9103 Phone 585 872 0010 Fax 585 872 0739 Toll Free 800 828 6308 Internet www ashly com 2002 by Ashly Audio Corporation All rights reserved worldwide Printed in USA 05 02 DPX100 0
16. times speed up as more and more limiting occurs The compression ratio also increases This lets us main tain peaks fairly close to a constant ceiling level but al lows the illusion of increasing loudness as input level increases thereby preventing complete loss of dynamics when limiting 2 We incorporate a double release time constant When release time was set slow with a single time con stant transients such as mic pops caused a quick re duction in gain and a slow fade up making the action of the limiter very obvious With the double time constant release from gain reduction after a brief transient is al ways fast with a slower release after a sustained over drive When choosing a compressor limiter you can see that it is very important to listen to it in your particular application and see that it sounds the way you want There are lots of these devices with seemingly excellent specs which sound very different with real program material applied to them Peak Or RMS There are several ways of looking at a signal to determine its level A peak detector looks at the maxi mum voltage a signal reaches regardless of it s waveform while an RMS root mean square detector looks at the energy in a signal regardless of the short term voltage levels This makes a peak detector the correct choice for preventing clipping overmodulation or tape saturation while an RMS detector can be used to restrict material to a given lo
17. to help bring out a lead vocal or instrumental solo in a cluttered mix The com pressor is also a great corrective tool when working with singers whose own dynamic control is less than perfect A little compression helps to keep their quieter lines from becoming buried in the mix Experimentation is highly recommended Voice Over Compression Ducking The compressor limiter can be used to automati cally reduce music to a background level when an an nouncer is speaking In this scheme only the music signal is actually gain reduced by the limiter However the de tector is connected to respond to an announcer s voice instead of the music s peaks Voice Over compression assumes you are already using some sort of mixer to com bine the music and mic signals Use the direct out send of the mic channel to feed the detector input on the CLX unit Note Be sure to use a mono plug for the CLX detector input Then use the Threshold and Ratio con trols to determine when and by how much the announcer voice affects the music level De Essing A special type of saturation problem often en countered in recording is the sibilant Ssss sound of the human voice High frequency sibilant sounds can reach very high energy levels so that a voice that is otherwise undistorted breaks up on the esses producing a raspy un desirable sound With analog recording to magnetic tape high frequencies tend to saturate the tape sooner and co
18. ASHLY DPX 100 Graphic Equalizer Compressor Limiter Operating M anual 10 T 2 4 PP M E idis qs m 453522 g 5 15 8 Range 0000000000 000000000 9 3 0 uem 5 yo 8 5 S id s e OTe 1 5 2 H 0 zi fe 2 Ls MF t8 029 t 48 2 Sig Cl 80 2 Y m m piss as 5 Y gt 2 ns 20 sa O Power Threshold Ratio Attack Release Output Level In ASHLY AUDIO INC 847 Holt Road Webster NY 14580 9103 Phone 585 872 0010 Toll Free 800 828 6308 Fax 585 872 0739 Internet www ashly com Operating Manual 100 Graphic Equalizer Compressor Limiter Table Of Contents 1 INTRODUCTION RAO eR o AUR ae eod 2 UNPACKING RR Ee ROI ew Cs t d uu ede mus hue 3 AC POWER REQUIREMENTS 4 MECHANICAL INSTALLATION 5 EQ CONTROLS 4s exa dae GERE DEL ATCP ES DEDI CLA eis Sil ereet IPs Rid eden Reps Wed e RE ee Ree I2 AIM peake aion tee Did GRAN DC oe 5 4 Filter wh 9 9 BQ In QUE eet hed ea bebe
19. For installations where it is desirable to protect the front panel controls from tampering or accidental misadjustment use the Ashly security cover Installation is simple and does not require removal of the equipment from your rack See your Ashly dealer for details Ashly Security Cover Installation 5 EQ CONTROLS 5 1 EQ Boost Cut The individual equalization faders adjust the boost or cut at each filter frequency By adjusting a com bination of faders an overall frequency response can be developed and the physical position of the faders will give an approximate visual indication of this response 5 2 Gain The gain control adjusts the overall gain of the equalizer when the EQ switch is in It is generally used to compensate for level changes due to the equalization process but can also allow the equalizer to adjust overall system level and gain structure Overall gain with this control is from 6dB to 5 3 Range This switch selects the operating range of the individual equalization faders to either 15dB or 6dB The 15dB settings should be used when much equaliza tion is needed The 6dB setting allows finer resolution on the fader settings 5 4 HPF Hi Pass Filter The high pass filter can be used to supplement the frequency response achieved by the bandpass filters It s function is to roll off low end response to eliminate subsonic interference like wind noise floor rumble and boomy microphone pop
20. ain monitoring level the feedback will stop 4 Try to determine the feedback frequency and then equalize it by adjusting the center frequency band width and boost cut controls of your parametric equal izer Note a graphic equalizer can also be used although with less accuracy After eliminating the problem fre quency try to further define it by sharpening up the band width reattacking the frequency control and making the cut shallower if possible 5 As soon as the first feedback frequency has been removed the compressor limiter will automatically bring up system gain until another feedback point is in duced Repeat the equalization procedure until it becomes impossible to distinguish individual predominant feed back frequencies 6 Write down EQ marks for safekeeping if nec essary and return all mixer EQ master gain and com pressor limiter gain controls to normal operational settings Altering the Texture of Musical Instruments It would be impossible to mention here all the ways that compression is used to create new sounds with familiar instruments Some typical uses are 1 Creating a fatter kick drum or snare sound 2 Thickening acoustic guitars 3 Adding punch and sustain to electric bass or guitar In general use a gentle compression ratio say 4 1 with a 10 mS attack time 0 1 Sec release time and a low enough threshold to cause 6 to 10dB of Gain Re duction Try using this effect
21. al compressor limiter is adjusted for slow release times transients such as mic pops may cause a severe reduction in gain followed by a slow fade up making the action of the limiter very obvious With ASHLY 5 C2 C2 Operating Manual DPX 100 Graphic Equalizer Compressor Limiter M IN 7 ASHLY 2 Model DPX 100 Made In USA CAUTION eo 100 120VAC A 50 80Hz 12W Not Open INPUTS are Active Balanced alanced Or Unbalanced 3 2 4 Female Shown m Com Detec Use RIN Q Output 3 the double time constant release from gain reduction af ter a brief transient is always fast with a slower release after a sustained overdrive 6 6 OUTPUT LEVEL Output level control is provided to fully cut or restore up to 18 dB of system gain For unity gain set the control to 0 NOTE When the compressor limiter is switched out the output control still functions 6 7 IN OUT SWITCH This switch enables you to quickly hear the com pressor limiter in or out of the audio chain When the switch is in the out position all limiting and compres sion controls and functions are bypassed with the excep tion of the gain and output controls which continue to function as straightforward level controls 6 8 THRESHOLD GAIN REDUCTION DISPLAY As soon as the threshold level is reached the yel low LED illuminates Dependin
22. an eliminate one or two feedback points by setting one or two sliders for no more than a 6dB cut Often you can find a feedback point by boosting sliders in succession to determine which frequency ranges contain the feedback modes and then cutting those ranges Be very careful in this process to avoid explosive feedback and possible sys tem and hearing damage If you find feedback points with many equalizer bands remember that cutting every band may not help all you will do is reduce system gain The combination of a graphic equalizer for tone control and a parametric equalizer such as the Ashly PQX 571 or PQX 572 for feedback control is highly recommended Console Channel Equalization Many mixing consoles provide only simple equal ization for individual channels If your console has chan nel inserts you can patch your graphic equalizer into a channel that s being used for something important and use it to tailor the sound of this channel exactly the way you want Large Room Equalization Large rooms tend to suffer from multiple reflec tions with long time delays long reverberation times and ring modes all of which lead to reduced intelligibility and a generally muddy sound As sound travels long distances through the air high frequencies are attenuated more than low frequencies In general large rooms ben efit from some low frequency roll off high frequency boost and attenuation of ring mode frequencies As in
23. ansconductance amplifier Using the inherent match ing obtained by integrated circuit technology these de vices have very predictable control characteristics Tracking within 14 over a 40dB range 15 common Not only do the control characteristics match well from unit to unit but they can easily be made exponential loga rithmic so that even increments of control voltage pro duce even increments of gain change in decibels The response time is also very fast The problem with simple transconductance am plifiers is that like FET VCA s they can handle only very small signals so the noise performance is poor A num ber of linearizing circuits have been devised to minimize this problem but even the best transconductance amplifi ers have an equivalent input noise of about 80dBv which compares poorly to straight linear amplifiers The best analog compromise to date is the class AB current ratio multiplier Early implementation of this circuit used two matched pairs of transistors one pair of NPN s and one pair of PNP s The problem here is that excellent matched integrated NPN pairs were avail able but integrated PNP s were not The PNP s had to be hand tested and matched Careful trimming was neces sary for low distortion and even minor temperature changes made re trimming necessary because of differ ing characteristics between the two types The Ashly VCA The Ashly VCA is an integrated current ratio mul
24. ated until the engineer is satisfied that the significant problem frequencies have been corrected The major problem with this approach is that the feedback can easily get out control and the engi neer ends up dashing back and forth between the mixer volume controls and the equalizer controls while every one in the room plugs their ears and prays it will end soon The Ashly DPX 100 can turn this procedure into a fast painless job eliminating loud feedback levels and the possibility of speaker or ear damage Procedure 1 Set up the DPX 100 limiter controls as follows Output level control to 20dB Input Gain control to OdB Threshold control to 30dB Ratio control to infinity Bese ASHLY 9 Operating Manual DPX 100 Graphic Equalizer Compressor Limiter e Attack time to 5mS f Release time to 1 Sec g Limit switch IN 2 Using a 1 3 octave 31 band or parametric equalizer set the EQ controls to a flat setting and if the equalizer has an overall volume control boost it by 10 to 15 dB 3 Open up several microphone input channels to a normal operating level with typical EQ settings and turn the console master fader up to a louder than normal setting At this point the system should be well into feed back but the room volume will be constant due to the action of the limiter You can listen to the feedback at any level you like by simply varying the limiter output level control although below a cert
25. cient drive signal Make sure you are send ery 2 ing a nominal 0 dBu line level signal to the 31 L VCA 1 equalizer Most noise problems occur because po gain is applied to audio signals too late in the REDUCTION DESETAK chain For best performance apply gain to in ENO LIMITER dividual source signals as early as possible like at the mixer input preamp section As gain in DETECTOR IN OUT 1 1 pe L creases it also boosts the noise content of that x signal Any cumulative noise built upina mixed P NSERT signal will only be increased by using an equal izer as gain device so make every attempt to 11 Equalizer Troubleshooting Tips No Audio Output Check AC power is the pilot light on Check in out connections are they reversed Are you sure you have an input signal EQ Controls Do Nothing Is the master EQ switch in The lowest and highest frequency sliders may be beyond the range of the program material or speakers and may produce little or no audible effect Peak Light Flashes or Stays On All the Time If the peak light flashes the signal level to the equalizer is too high Turn down the gain If it is on all the time disconnect the input and output cables If it is still on the unit must be returned for service 14 operate the equalizer with as little gain as pos sible Note Unshielded cables improperly wired con
26. crophonics high cost and the need for both high voltage and filament power supplies Over the years the need for good low cost solid state VCA brought about many innovative ap proaches A good example is the electro optical at tenuator where a photocell is used as one leg of a potentiometer Since the photocell behaves as a true resistor distortion and noise are very low Unfortu nately the response time of photocells is slow and un predictable so their use in a fast peak limiter is really not feasible Also the matching between units is very poor so that stereo tracking is not possible without te dious hand matching of photocells Another approach uses a field effect transis tor FET as a variable resistor Here at least the re sponse time is fast in the nanosecond range but matching between units is still poor requiring hand matching for stereo An additional problem is that a FET will only act as a pure resistor with very small signals applied so it is necessary to attenuate an input 12 ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter signal before the gain control FET and then amplify it again Of course this results in less than ideal noise per formance and imposes a frustrating trade off less noise more distortion A number of VCA s based on the exponential volt age current characteristic of a bipolar junction transistor have been used One of the most common is called a tr
27. dvantage is the induc tor itself An inductor is a coil of wire with a core of some sort Inductors are susceptible to hum fields and they are large and expensive Other equalizers use the same basic approach but replace the inductor with a simulated inductor which is actually a circuit comprised of an amplifier a capaci tor and a couple of resistors This adds parts but is less expensive than a real inductor The problem with this approach is that simulation is less than ideal it produces an inductor with high resistive loss resulting in poor curve shape when used in a filter Another problem with RLC designs is that large capacitors must be used for the lower frequency filters limiting the choice to large expensive non polar types or electrolytic capacitors with poor audio performance Also when this filter type is combined with a potentiometer to adjust the equalization the resistance of this pot affects the of the filter so that a little equalization produces a much broader curve than a lot of equalization The other filter approach is a true bandpass fil ter This can be made with no inductors and more practi cal sized capacitors the Q is easily set and remains constant and the parts count is reasonable there are sev eral types of bandpass filters suitable for this job Ashly uses a Q enhanced Wein bridge filter Because it is a symmetrical design using matched tuning components the Q
28. en tion which takes you away from more important jobs The need for a fast acting reliable automatic gain control is answered by limiters and compressors WHAT COMPRESSORS AND LIMITERS DO LIMITING In any musical program are constant changes in loudness It is the job of a limiter to detect when the vol ume has exceeded a predetermined maximum safe level and to then turn down the volume When the incoming signal returns to its original level the limiter should re spond by restoring the gain to normal Thus when the level is within a specified safe range the limiter has no effect When an occasional peak occurs the limiter re sponds This situation is completely analogous to manual gain riding except that it occurs faster and more consis tently COMPRESSION A very significant difference in dynamic range is achieved simply by changing the relationship between nomi nal signal level and threshold as a result of either increas ing the GAIN and or decreasing the THRESHOLD control The most interesting effect to be noted however is seen by comparing the original input signal with the output signal The quietest portions of the original signal will be effec tively increased in volume while the loudest portions of the original signal will be decreased In effect both ends of the dynamic spectrum will be pushed toward the middle This is quite different from simple limiting where only loud peaks are subjected to ga
29. fast transients such as hand claps snare drums or other percussive sounds a fast attack time is usually desirable so that the limiter can respond in time to control the peak level On other types of program ma terial a slower attack time may be preferred An abrupt attack may on some material square off the top of a waveform producing a distorted sound The DPX 100 pro vides continuously variable attack times from 200 micro seconds to 20 milliseconds 6 5 RELEASE TIME Another parameter which affects compressor lim iter performance is release time or the time required to restore system gain to normal after the input signal has fallen below threshold level Again proper release time will depend on the type of program material being processed and the way in which the limiter is being used When subtle limiting is desired slow release times are often chosen to avoid condition referred to as pumping or breathing This occurs when overall gain is modulated up and down by repeated peaks which are followed by quieter intervals If the release time is set too fast then the overall level will jump up and down producing an objectionable and unsettling effect Note that in some cases an individual track or channel which seems to be pumping may sound acceptable when heard in context of a complete mix A unique feature of Ashly Compressor Limiters is the incorporation of a double release time constant When a convention
30. g on how far the input level rises above threshold successive red LED s will il luminate indicating gain reduction Gain reduction can best be described as the difference between input level and the resulting change to output level For signals below threshold there will of course be no gain reduc tion that is a 10dB increase in input will yield a 10dB increase in output For signals above threshold however output level will increase only to the extent that the ratio control allows With a high ratio say 20 or so it will take 20dB of increased input level to increase output level by 1dB With a gentler ratio of 3 1 input signals above threshold will be gain reduced at the output by 1 3 In other words with threshold set at OdB a signal peak at 12 dBV that is 3 1 compressed ratio at 3 will produce only 4 dB 12 3 at the output and 8 dB of gain reduc tion has occurred 12 dBV input minus 4 dBV output 8 dB reduction 6 9 INPUT OUTPUT METER SELECT While the Gain Reduction display accurately rep resents the action of the limiter comparing input to out put levels in real time is somewhat more intuitive and is made simple using the input output meter select switch The input meter takes its signal just after the gain con trol and will indicate input signal level regardless of out put levels or limiter settings The output meter display takes its signal from the actual output of the unit so ev ery control that affec
31. gin is known as headroom and may range from 10 to 25 dB Lowering our standard operating level to leave ourselves some headroom helps prevent distortion but at the same time it moves our average program level closer to the noise floor thereby compromising signal to noise performance It becomes apparent that to get most ASHLY 11 Operating Manual DPX 100 Graphic Equalizer Compressor Limiter out of an audio system you have to keep your standard operating level as high as possible without risking distor tion GAIN RIDING One solution to the noise vs distortion trade off is to keep your hand on the level control and manually adjust gain to suit the program Indeed there are times when this approach is entirely satisfactory However in most types of music there are instantaneous short dura tion volume peaks or transients which would be difficult to anticipate and impossible to respond to with manual gain riding you simply could not bring the level down fast enough In many situations this can present real prob lems For example in recording an extra burst of enthu siasm from a lead singer might overload the capabilities of your recording tape causing ragged distortion and ne cessitating another take In sound reinforcement a sud den burst of energy through the system can blow fuses or even damage loudspeakers In addition to the problem of response time with manual gain riding it also requires your constant att
32. good and is adequate for most musical program material However some types of audio equipment such as cassette tape recorders have a very narrow useful dy namic range What is it that compromises the dynamic range of this equipment The useful operating region of a piece of audio equipment is squeezed in between noise and dis tortion As program level decreases it approaches what is known as the noise floor and if the volume of the program material goes lower still it is engulfed by the noise The noise floor or minimum constant noise level will consist of hiss hum transistor noise tape hiss buzz and whatever noises are inherent in the medium When the program level is considerably higher than the noise floor our hearing masks the noise and it is not a prob lem However when listening to very quiet sections of a program for example a pause between movements of a string quartet the noise can become very bothersome At the other end of the loudness spectrum the limitation on dynamic range is usually distortion either in the form of amplifier overload tape saturation or A to D clipping In most transistorized equipment the transi tion from clean undistorted operation to severe distor tion is very abrupt Therefore it is common practice to operate a piece of equipment at a level that is somewhat below the distortion point leaving a margin of safety for unexpected transient volume peaks in the music This safety mar
33. in a single rack space product Both equalizer and compres sor limiter can be used as stand alone processors or can be automatically chained together with a back panel switch The graphic equalizer section uses professional quality 25mm faders for maximum resolution and long life Ashly graphic equalizers use Q enhanced Wein bridge filters with interleaved summing for constant Q low ripple and minimum filter interaction The Ashly compressor limiter circuit was de signed in response to the need for universal peak sensi tive automatic gain control AGC devices with exceptional audio performance and rugged durability The result is a wide bandwidth ultra low distortion low noise voltage controlled amplifier which is versa tile and highly listenable Premium components are used throughout the DPX 100 and computerized automatic assembly equip ment verifies that each component s electrical specifica tions are within tight tolerances before becoming part of the circuit assembly Each finished unit is then tested twice before leaving the factory guaranteeing you a worry free professional product for many years Please read this instruction manual thoroughly before operation so that you may realize all the features and benefits the Ashly DPX 100 has to offer 2 UNPACKING As part of our system of quality control every Ashly product is carefully inspected before leaving the factory to ensure flawless appearance
34. in reduction More than anything else it is this double ended effect which dis tinguishes compression from limiting Compression is further differentiated from limiting by careful selection of attack and release times When limiting is employed to protect an audio system against transient volume peaks and possible overload attack time is usually set as fast as possible consistent with distortion free performance Release time would also be relatively short so that the output signal would be restored to normal as quickly as possible after the transient Compression is frequently used to keep over all signal level within a specific dynamic range and for this application slower attack and release times are usually chosen This approach is analogous to our manual gain riding example where our operator is fad ing the music up and down to keep it fairly constant but is doing it slowly enough so that the listener is un aware that the gain is being altered Voltage Controlled Amplifiers Early VCA s were based on vacuum tubes with a remote cutoff characteristic The tube would sim ply change its gain in response to a changing bias volt age Tubes developed for this purpose did an excellent job in fact they could exceed the noise and distortion performance of today s best solid state VCA s Unfor tunately they also had some serious disadvantages pe culiar to tubes change of gain and matching as aging took place heat mi
35. m bined with the internal high frequency boost record pre emphasis on standard tape decks the need to control sibilants becomes apparent The solution is frequency dependent limiting which is easily accomplished with the DPX 100 By in serting an equalizer into the Detector Patch point and boosting the equalizer at high frequencies in the vicinity of the sibilant the limiter s detector circuit becomes more sensitive to this particular range of frequencies and so will limit the bothersome sibilants more than other fre quencies Realize that this technique is very different from simple equalization Equalizing a sibilant vocal by cut ting high frequencies would result in a loss of important high frequency information at all times whereas de essing has no effect whatsoever on the signal except at the in stant of the sibilant At that moment the Ashly limiter will reduce overall gain Frequency response is unaf fected and the sibilant is controlled 10 ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter 9 DESIGN THEORY Graphic Equalizers The Basics While most graphic equalizers look very much the same there are several important differences in the circuitry used to implement various designs Perhaps the major differences are in the filters Some equalizers use a filter made of a capacitor an in ductor and a resistor RLC filter The advantage here is simplicity but the real disa
36. ol to make an audio signal appear louder A good example is in broadcasting where com peting stations with identical transmitters and power at tempt to sound louder than each other Since they are all restricted with respect to maximum audio level modula tion their best tactic is to squeeze the dynamic range of their programs to just a few dB The audio output level of the station virtually never changes and the listener perceives this continuous high level sound as being louder than the same material in an uncompressed form Although both compressed and uncompressed programs reach the same peak levels the compressed signal stays near peak level more of the time and thus sounds louder This tech nique makes the broadcast more intelligible over ambi ent noise and increases the geographical area over which the broadcast is audible to the listener Additionally this compression technique is extremely useful for FM and infrared transmission systems for the hearing impaired 8 3 Special Effects Compression For Feedback Control A common ritual in sound system set up is equal izing the room to remove feedback This is generally accomplished by turning up system gain to purposely in duce feedback searching for the center frequency of the feedback and then equalizing at that frequency to remove the feedback Once this frequency has been cut system gain is again increased to induce another feedback point and the whole procedure is repe
37. onents Try using the suggested balanced input and output hookups if the other pieces of equipment used in conjunction with the DPX 100 have balanced inputs and outputs Noise can also be caused by insufficient drive levels Make sure you are sending a nominal 0 dBV line level signal to the unit 12 WARRANTY INFORMATION Thank you for your expression of confidence in Ashly products The unit you have just purchased is pro tected by a five year warranty To establish the warranty be sure to fill out and mail the warranty card attached to your product Fill out the information below for your records Model Number Serial Number Dealer Date of Purchase 13 SPECIFICATIONS EQ Input Type Active Balanced Impedance 20KQ Balanced 10KQ Unbalanced Level een 23dBu Input Connectors 1 4 Phone Jack XLR Pseudo Balanced 200Q Balanced 1002 Unbalanced Output Type Impedance Max Level Output Connectors Frequency Response THD 20Hz 20KHz IM Distortion SMPTE Output Noise 20Hz 20KHz Gain Control EQ in all faders flat 20Hz 20KHz Filter Type Bandwidth Tolerance c e reu RANGE CE E ERR Subsonic Filter 23dBu lt 01 20dBu lt 01 20dBu lt 100dBu to 6dB Constant Q Wein Bridge 2 3 octave 3 6 or 154 18dB octave 20Hz Compressor Limiter 1 tation 15dB Ratios 2 1
38. ove which gain reduction occurs When the threshold LED comes on that means that gain reduction is beginning to occur due to input signal peaks exceeding the selected threshold in dB 6 3 RATIO This control determines the resultant change in output level to changes in input level for all signals above threshold The numbers printed around the ratio con trol are calibrated in db and indicate the increase in input above threshold required to produce 1db in crease in output This can be expressed conveniently as a ratio If the output remains constant no matter how high the input level we have an infinite input output ra tio It should be remembered that the ratio control has no effect on signals which are below threshold There is a common but incorrect notion that lim iting always implies the use of an infinite ratio Although there are times when an infinite ratio 15 desirable there will be situations where infinite or limiting ac tion is neither appropriate nor necessary In fact it should be noted that an infinite ratio setting is likely to cause noticeable side effects in the sound and may not be us able on programs where subtle control is desired 6 4 ATTACK TIME The response of the compressor limiter to signal levels above threshold is further defined by the attack time control Attack time is the amount of time it takes to attenuate the output level after threshold has been reached For very
39. protect against input overload With digital re cording the information stored on tape hard disk optical disk etc is either a 1 or 0 so actual signal level on the tape is not the concern it is with analog recordings in fact it is not even a user controllable parameter What is of concern however is the signal level applied to the A D analog to digital converters If clipping occurs at the converter input stage the resulting distortion is most un pleasant and will be recorded digitally as if they were part of the original audio signal forever mixed with the audio To prevent converter distortion while preserving the extended dynamic range of digital recording look up the max input level of your recorder converter and set up the limiter as follows Set Gain to 0 Set Threshold to 2 3 dB below max converter input Set Ratio to 10 Set Attack to 2 mS Set Release to 2 Sec Set Output level to 0 N e Ov ta ROO If you are exceeding threshold frequently your input signal is probably too high and should be turned down Of course every situation is different so experi mentation before final recording is always a good idea but this is a good starting point To obtain a gentler limiting action at the expense of some dynamic range decrease the threshold to 15 and the ratio to 3 5 This is also a good starting point for analog recording Broadcasting Eri 2 Compression has long been used as a to
40. s The high pass frequency is fixed at 20Hz with an 18dB octave slope 5 5 EQ In Out This switches out the boost cut controls and EQ gain adjustments This way the effect of any equaliza tion can be compared to a flat response This switch does not defeat the high pass filter 5 6 Sig and Clip LEDs The signal present LED comes on when a signal greater than 20dBu arrives at the EQ input The clip LED indicates any EQ signal level exceeding 19dBu ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter di amp 6 10 j 15 4 22 Gain Gain Reduction dB Input Output Level dB Clip OO OOOOOOOO0 18 15 12 9 5 3 0 3 6 9 20 02 3 Output am input Threshold Ratio Attack ae iain bs o 9 oO 6 COMPRESSOR LIMITER CONTROLS 6 1 GAIN The Gain control is used to adjust incoming sig nal level to the VCA circuit It is always active so switching out the limiter function has no effect on this control Used in conjunction with the input output level meter display this control is useful for setting up optimal system levels This control should normally be left at 0 to achieve accurate threshold calibration 6 2 THRESHOLD The threshold control has a range of 40dB to 22 dB allowing applications from low level compres sion to high level limiting The threshold control de termines the audio level ab
41. stop a change of direction and instant acceleration again Since speaker diaphragms are subject to the laws of physics they won t take this kind of punishment for long The diaphragm may shatter or its voice coil may overheat In addition to the damaged caused by sustained overload the speaker may also be damaged by occasional one shot high level overload for example the sound of a microphone falling face first onto a hardwood floor Even 8 ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter if this type of transient doesn t destroy a speaker outright it may damage the speaker surround in such a way as to cause mechanical abrasion and future failure Alternatives For Sound Installations To install a compressor limiter in a sound sys tem using a passive crossover insert it between your mix ing console output and the power amplifier input For systems using electronic crossovers there are two ways to use a compressor limiter It may be inserted between the mixer output and the crossover input in which case it will act on the entire audio frequency spectrum Alter nately if the limiter is inserted between an output of the electric crossover and the input of a power amp it will only affect a specific band of frequencies Recording The Ashly limiter can be used to prevent tape saturation in analog recording Also with modern trends toward inexpensive digital recording it remains neces sary to
42. sual reference provided by the slider posi tion gives an approximate idea of the frequency response generated with the lower frequencies on the left and higher frequencies on the right To use the power of an ASHLY 7 Operating Manual 100 Graphic Equalizer Compressor Limiter equalizer effectively you need to translate your idea of the tone you want to produce into a range of numerical frequencies This is simple after a little practise Here are a few references which are useful for starting points Very low bass the wind in a kick drum almost felt as much as heard 40Hz 80Hz The low register of a male voice 200Hz The low register of a female voice 350Hz Lower midrange warmth frequencies 400Hz 1 KHz Upper midrange harshness snare drum bite hot sound 2 5KHz 4KHz Sibilance sss sounds cymbal sizzle 8KHz 15KHz Try using these starting points as a guide when you want more or less of these types of sounds Adjust by ear from there It is always a good idea to remember that a little equalization usually works out much better than a lot and that there are many audio problems which can not be solved with equalization alone Feedback Control A graphic equalizer can be used to provide some control over moderate feedback problems but does not have enough flexibility or resolution to handle severe situ ations You will achieve the best results when you c
43. the case of feedback control a graphic equalizer can help reduce an isolated ring mode or two but a tunable nar row band equalizer such as a parametric is more effec tive here 8 2 COMPRESSOR LIMITER APPLICATIONS As the functional name implies a compressor limiter can be divided into two basic categories limiting and compressing When used as a protective device to prevent audio levels from overloading systems such as tape recorders power amplifiers speakers or transmit ters it is generally referred to as a limiter It may also be used to create special effects and unusual sounds for recording and musical performance by deliberately reducing the dynamic range of a signal creating a much louder or fuller sounding signal without increasing the loudness peaks in which case it is referred to as a compressor The Limiter As A Protective Device The DPX 100 compressor limiter section pro vides fast and accurate gain control for the prevention of sound system overload due to unexpected transients Sound system distortion is usually the result of amplifi ers running out of power in which case nice round wave forms turn into harsh sounding squared off waveforms Looking at it from the perspective of the speaker dia phragm this means that whereas in normal operation the diaphragm is required to accelerate slow down smoothly change direction and accelerate again distorted opera tion requires an instant acceleration instant
44. tiplier circuit It has low noise 90dBv low distortion 05 excellent response time and tracking and does not suffer from thermal drift The noise and distortion are at state of the art levels and the circuit is consistent in mass production with minimal trimming and no hand selection of transistors Detectors It would seem that of the two components in a compressor limiter the VCA is the more critical since the audio passes through it and the detector only provides it with a control voltage Experience showed us that both are crucial to the overall sound and that if anything the detector s performance is the harder to judge by conven tional measuring techniques While the VCA is doing its job if it has low noise and distortion the detector must con stantly adjust the gain of the audio path in a manner which keeps the level under control while sounding acceptable to the listener This constantly changing gain is a dynamic action while conventional audio measurements like noise and distortion checks are Static at a constant level We became painfully aware of this problem with some of our earlier limiter prototypes which measured fine and sounded terrible This led us to use a purely subjective approach in the design of the detector we did a lot of listening to de termine what sounded good and what didn t Two important features emerged from this re search 1 We designed the detector to let the attack and release
45. ts the output will also have an effect on output meters Used in conjunction with the gain re duction meters input output meters prove to be an ex tremely useful diagnostic tool when working with system dynamics and level control 7 CONNECTIONS AND CABLES 7 1 Balanced vs Unbalanced Audio Connections Balanced signal connections are preferred in pro audio applications because of their improved immunity to induced hum and noise A properly shielded and wired balanced input stage on any audio product will reject most unwanted noise RFI EMI picked up by the cable as well as minimize ground loop problems Therefore it is always advantageous to use balanced connections when running signal more than ten or fifteen feet although par ticularly noisy environments may require that even short patch cables be balanced Unbalanced connections are used mostly for short distance high level signals 0dBu nominal Most exter nal EMI noise pick up will be masked under the noise floor of the signal assuming there is little or no gain fol lowing the unbalanced signal If a gain stage does follow a signal or if externally sourced noise persists use bal anced connectors 6 ASHLY Operating Manual DPX 100 Graphic Equalizer Compressor Limiter mpressor Limiter tector Return Ducking Input Mono Plug For Ducking ING Detector Send OOQ Detector Chain e mma Jl Out T Graphic Equalizer 4
46. udness When an RMS limiter is used to pre vent clipping the result is unpredictable For instance a flute and a snare drum which are limited to the same RMS level might have peak levels as much as 30dB apart Use peak limiters to prevent clipping ASHLY 13 Operating Manual DPX 100 Graphic Equalizer Compressor Limiter 10 BLOCK DIAGRAM Distorted Sound This will only be caused by too much signal which will show on the Clip LED If the D LED is not flashing is an overload some SIG where else in the signal path Adjust the rela tive gain of each component in your chain to 5 t aem keep everything at a comfortable level bs EQ 6dB 15dB INBUT GAIN Excessive Hum or Noise 3 15 BAND EQ Hum will usually be caused by a ground Te Me L HPF In Out EQ In Out loop between components Try using the sug api gested balanced input and output hook ups if the other pieces of equipment used in conjunction ueri m with your equalizer have balanced inputs and j P outputs 1 LIMITER mall INPUT CLIP Noise excessive hiss can be caused by ian INPUT OUTPUT METERS insuffi
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