Ashly SC68 User's Manual
Contents
1. The SC 68 is unity gain device except for the notches in the frequency response and has a headroom of 20 dBV The nominal operating level is 0 dBV It can be inserted anywhere in the signal path between the mixer and the crossover or power amp in passive crossover or full range systems 3 INTRODUCTION The SC 68 Parametric Notch Filter is a cut only equalizer which is capable of producing relatively sharp dips in the frequency response of an audio system It is useful for notching out narrow segments of the audio frequency spectrum thereby reducing problems such as feedback cabinet resonances hum video sync buzz and single hot notes on musical instruments The SC 68 is useful in professional sound reinforcement recording and broadcast applications with audio performance to meet the most exacting requirements The 56 68 includes a setup system to aid an operator in eliminating feedback in sound reinforcement Standard procedure in tuning a room is to purposely induce system feedback and then equalize the system at the predominant feedback frequency When the SC 68 is used in the SETUP mode it automatically increases system gain until feedback occurs and then holds the feedback at a controlled low level while the operator identifies and notches out the offending frequency When that has been done the limiter again increases system gain causing controlled feedback at new frequencies These can then be notched2. STRANDS SHORTS ETC ARE THE MOST COMMON PROBLEMS MAKE SURE YOU USE GOOD QUALITY CABLE eae WHEN IN DOUBT GET IN TOUCH WITH YOUR ASHLY DEALER OR CALL THE FACTORY DIRECT 800 828 6308 New York State dial 716 544 5191 14 OHM The unit of electrical resistance or impedance PHASE Describes 06 well two signals in step In phase means that and negative peaks in two Signals occur together while out of phase means they do not occur together Variations in signal timing as well as polarity can make two signals in or out of phase or anywhere in between Phase is usually measured in degrees where 0 degrees is in phase 180 degrees is out of phase and 90 degrees is in between sometimes called quadrature PREAMPLIFIER The first stage of amplification designed to boost very low level signals to line level 0 measurement describing the sharpness or broadness of filter 1 SHELVING Describes an equalization action where all frequencies above or below a particular frequency are boost or cut TRANSIENT A sudden burst of energy in an audio signal such as a blast ina microphone the sound of a snare drum or a deep scratch in a record Transients frequently reach peak levels of 10 to 30 dB above standard operating level and may cause distortion or even damage to equipment UNITY GAIN Output level Input level WIRING PHONE PLUG AND XLR A stereo phone p
3. ASHLY 5 68 PARAMETRIC NOTCH FILTER OPERATING INSTRUCTIONS ASHLY AUDIO INC 100 FERNWOOD AVE ROCHESTER N Y 14621 716 544 5191 TOLL FREECEXCEPT N Y STATE 800 828 6308 20 TABLE OF CONTENTS INTRODUCTION UNPACKING FRONT AND BACK PANEL LAYOUT INPUT OUTPUT AND POWER CONNECTIONS EXPLANATION OF PARAMETRIC NOTCH FILTERS THE SC 68 S CONTROLS FILTERS SETUP SYSTEM USING THE SC 68 TO REMOVE FEEDBACK DEFINITION OF TERMS TROUBLE SHOOTING TIPS SPECIFICATIONS AND BLOCK DIAGRAM GRAPH OF KEYBOARD MUSIC STAFF FREQUENCY NUMBERS 11 14 15 16 control clockwise is equivalent to moving the notch up the keyboard and counterclockwise moves it down The Bandwidth control Octaves determines the number of notes or range of frequencies which will be included in the notch This is shown in the illustration as a bracket encompassing roughly 2 1 2 notes on the keyboard since the Octaves control is set at 3 a fairly broad notch Turning the control clockwise would make the notch progressively narrower so that at its narrowest setting of 03 Octaves less than one note of the scale would be effected As noted earlier each of the 8 filters is identical except for the range of frequencies it is designed to cover Any filter may be adjusted as desired without regard to the other filters with one exception instead of setting two sharp filters to nearly the same center frequencies it is preferable to use just one
4. Originally defined by the telephone company to measure line levels dBY Decibel Volts an update of the dBm definition where 0 dBY the same voltage level as 0 dBm but with no regard to power or impedance 0 dBY 0 778 Volts This unit is much more appropriate for modern audio equipment with high impedance inputs and low impedance outputs 14 MIDDLE 4 ZH CONCERT ie le 1 110 1116 1119 l 111 5 LEGI 1 1111 FER TI EII lt SDINOWYVH 5
5. a the curve above the axis again represents the frequency response of a room with a 92 Hz resonance The curve below the axis represents the notch which can be created with an SC 68 which is an exact reciprocal of the room resonance and which will have the desirdd effect of ne ve resonance Notch Filter The result of the correctly tuned notch on the room response is shown above The problem has been fixed and no unwanted side effects have been EXPLANATION OF PARAMETRIC NOTCH FILTERS AND THE SC 68 S CONTROLS Types Of Equalizers Used In Audio An equalizer is a filter or a group of filters working together to shape the frequency response of an audio system The simplest filter is one that will produce a fixed amount of gain or loss boost cut over a fixed range of frequencies bandwidth filter will generally have the greatest effect in the middle of that band of frequencies which are being affected center frequency Since all of these circuit parameters are pre determined and fixed the filter s applications will obviously be limited to performing specific functions Graphic Equalizers were the first universal tone controls providing piece wise approximation of tot l frequency response All of these equalizers have common limitation some of the characteristics of equalization are fixed For example the center frequency and sharpness for each band of graphic are pre determined This lead
6. filter at the desired frequency and use a slightly broader bandwidth setting Some people make the mistaken assumption that if one filter set to 3 kHz can produce a 50 dB notch then 2 filters set to 3 kHz should produce a notch of 100 dB In fact it doesn t work that way but even if it did that would be missing the point Each filter by itself is capable of producing a notch accurate enough and deep enough to satisfy any real world requirement Setting two filters to the same frequency simply isn t necessary SETUP SYSTEM CONTROLS Because a parametric notch filter is particularly useful as an anti feedback tool in sound reinforcement applications a special setup system has been incorporated into the SC 68 to make the sound man s job even easier Essentially the system consists of a limiter which holds feedback at a listenable low level switchable listening modes to compare filtered and flat audio and a meter which indicates in dB the improvement in system headroom which has been achieved As a whole the SC 68 system is somewhat comparable to having a separate limiter compressor patched into parametric equalizer except that in the SC 68 both the limiter and EQ parameters optimized for the specific job of feedback control The operating mode of the SC 68 is selected by means of push button switches next to the meter Only one mode is used at a time In the SETUP mode the Setup system is activated In the OPERATE mode the entire
7. setup system is disabled and the SC 68 functions as a straightforward filter A brief description of the operating controls is given in Figure 7 On the next page PEAK LED The SC 68 peak indicator will flash on whenever signal levels in excess of 14 dBY are present With an overall system headroom of 20 dBY this light will warn you when you are within 6 dB of clipping The detection circuit monitors the circuit at 10 individual points including the input output and al 8 filters Since the SC 68 functions at unity gain or at loss Flashing peak light will indicate that high level signals are occuring somewhere in the audio chain prior to the SC 68 FILTER CONTROLS The SC 68 uses 8 filter secions with the only difference between filters being the range of frequencies spanned by the center frequency Hz control Once you understand one filter section you will understand them all 6dB at Center Frequency Hz Figure 6 Typical filter section SC 68 Referring to the above illustration of a typical filter from the 2 SC 68 the IN OUT switch allows quick A B comparisons of filtered and flat audio signals for each filter section making it easy to test the effect of any filter without disturbing the other filters Immediately below the switch the Amplitude control determines the depth of a notch at the center frequency Its effect is shown on the accompanying graph in wh
8. t attempt to actually operate the system in the SETUP mode as it will sound terrible and operate at a very low level The maximum gain before feedback of your system should be determined if the steps an page 9 are followed If you are still not satisfied here are some suggestions that might help Place all main system speakers and monitors such that they do not see any microphones that are to be fed to them Keep all guitar and keyboard stage amps away from vocal microphones Keep your stage volume as low as possible so your sound person has something to work with out front 2 Work vocal microphones as close as possible When you can t hear yourself have everyone else turn down rather than you turning up You have already determined the maximum volume of your PA system and if your fellow band members feel they can t turn down any more collect donations to pay for upgrading your present system ie separate mixes for monitor speakers more directional microphones better speakers etc 10 5 3 r E 5 3 x 3 SPECIFICATIONS AMPLITUDE 0 to 30dB FREQUENCY FREQUENCY low 16H2 800H2 3 low mid 22 RESPONSE 5dB 20Hz 20kHz 48224181 3 hi mid 180Hz OUTPUT IMPEDANCE 500 term with 600 Q or more 2 480Hz 24kHz HUM AND NOISE 870 eq In 25dBV eq out _ BANDWIDTH 3 octave 03 ociave DISTORTION lt 05 THD 400BV INPUT IMPEDANCE 40 i active b
9. will show the improvement in gain before feedback in decibels If two frequencies occur close together widen the bandwidth of one filter to suppress both frequencies with one notch It is possible that you ll have to increase the depth of some notches when frequencies nulled early the tuning process re establish themselves It s best to go around the procedure a few times until you are convinced that all notches are producing their desired effect without being any deener than necessary At any time in the tuning process you can switch between SETUP NOTCH and SETUP FLAT to re establish your reference Also switching each filter band in and out will verify the effect of each notch It may be necessary to adjust the SPEED control of the setup limiter to obtain stable readings The response time of the feedback modes in some rooms is slow and it is easily possible to tune right by a feedback point and miss it if you go too fast 6 When you re finished tuning reduce the master gain control of your mixer to a normal operating range and punch the OPERATE NOTCH switch The system is now ready for use Switch between OPERATE NOTCH and OPERATE FLAT to compare gain and sound quality but remember that the limiter is now disabled don t let the feedback run away ADDITIONAL NOTES AND HELPFUL HINTS System headroom may be improved even further by re positioning mics and speakers The SC 68 s meter will indicate any improvement Don
10. 1 3 octave graphic equalizer for removing feedback and room resonances Each band of a graphic is set to fixed center frequency which may or may not be close to the feedback frequency you are trying to correct A parametric notch filter on the other hand lets you tune to precisely the frequency in question without influencing any more of the frequency spectrum than necessary This is represented Figures 4 and 5 the next page pad INPUT V2 AMP ica Figure 1 5 68 Front amp Back Panels INPUT OUTPUT AND POWER CONNECTIONS gt This equalizer should be connected to a 3 wire grounded outlet supplying 120 Volts 50 60 Hz Power consumption is 12 watts 2 The INPUT is a 10K ohm active balanced type on a standard stereo phone plug The or in phase connection is on the tip and the or out of phase connection 15 the ring When feeding the equalizer from unbalanced sources connect the signal hot to the tip and the signal ground to the ring To use the input as a common unbalanced type simply use a mono phone plug in the usual way See Definition Of Terms Wiring page 13 The OUTPUT is a low impedance type typically about 50 ohms This should be terminated in a load of 600 ohms or higher to realize maximum headroom The output can be used as a balanced type by using a stereo phone plug wired in the same manner as the input or as an unbalanced type by using a mono phone plug
11. alanced 20Hz 20kH ng 1 POWER 120 VAC 50608 SW MAX IN OUT LEVEL 20dB 5dB at max cut 52 a sharp SHIPPING WEIGHT 42 Ibs BLOCK DIAGRAM BALANCED INPUT B AND AMPLIFIERS TROUBLE SHOOTING TIPS NO OUTPUT Check AC power is the pilot light on Check in out connections are they reversed Are you sure you have an input signal 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 DISTORTED SOUND 2 This will only be caused by too much signal which will show on the peak light If the light is not flashing there is an overload somewhere else in the chain Adjust the relative gain of each component in your chain to keep everything at a comfortable level Also make sure you are not trying to operate the SC 68 in the SETUP mode EXCESSIVE HUM OR NOISE Hum will usually be caused by ground loop between components Try using the suggested balanced input and output hook ups if the other pieces of equipment used in conjunction with your equalizer have balanced inputs and outputs Noise can be caused by insufficient drive signal Make sure you are sending a nominal 0 dBY line level Signal to the equalizer UN SHIELDED CABLES IMPROPERLY WIRED CONNECTIONS AND CABLE WITH BROKEN
12. be based on normal system operation and shouldn t change radically once the show starts 3 Switch the SC 68 to the SETUP NOTCH mode adjust the SETUP LEVEL control to 5 and the SPEED control The meter will be pegged to the right at this point 4 Increase your inate Waster oai control until feedback is heard and then continue to increase it another 10 dB or so Adjust the SETUP LEVEL control to obtain a feedback level which is above room noise but not louder than necessary Finally re adjust the mixer s master gain to obtain 0 dB reading on the setup meter Turning the gain up will move the needle to the left and turning the gain down moves the needle to the right After the meter has been zeroed do not adjust SETUP LEVEL or the mixer s gain since they wih throw off the meter calibration Fan 5 Estimate the feedback frequency and punch in an appropriate filter band Set the notch depth to 6 dB bandwidth to 1 octaves and slowly tune the frequency control until you find the first feedback point When you think you ve nulled it try narrowing the bandwidth as much as possible and adjust the cut so that it is just deep enough to cause the feedback to change to another frequency As a new frequency establishes itself the meter reading should increase slightly Notch out the new frequency and keep repeating the process until no further improvement can be obtained At this point the meter
13. educe to a minimum the possibility of transportation damage should the unit again require packing 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 i 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 AVAILABLE FOR INSPECTION BY THE CARRIER SAVE ALL PACKING MATERIALS UNTIL THE CLAIM HAS BEEN SETTLED oie md SETUP LEVEL CONTROL When the SC 68 is used in the SETUP mode the system will be induced to feed back and the built in limiter will hold the feedback at controlled low level while the operator determines the problem frequency and works on notching it out The SETUP LEVEL control allows you to control the actual listening level of the feedback in the room from moderately loud to very quiet Adjust it to suit your taste and then leave it at that setting OPERATING MODE SWITCHES Normal operating mode with filters active Filters bypassed SC 68 functions as a unity gain device Use this mode to compare noched and flat sound ASHLY Setup mode Filters active limiter active all setup controls active METER Gives a direct reading in dB of the relative improvement in system headroom as you notch out feedback frequencies For ease of reading the meter
14. ich a notch is centered at about 440 Hz and produces cut of 6 dB at the center corresponding to the 6 setting of the Amplitude control Turning the control clockwise will decrease the depth of the notch eventually obviating the effect of the filter when it is set to 0 Turning the control counter clockwise will make the notch ceeper producing a more pronounced cut at the center frequency The Center Frequency Hz control selects the frequency at which the notch will be deepest Frequencies above and below the center frequency will be proportionately less affected than the center frequency Frequencies which outside the range of the filter will be unaffected In this illustration the center frequency control is set to approximately 440 Hz which is shown on the keyboard to be equivalent to the note A above middle C Turning the Hz Figure 4 Graphic Equalizer In Figure the curve above the axis represents the frequency res ponse of a typical problem roon exhibiting a resonance at 92 Hz The curve below the line represents acut that could be made by a typical 1 3 octave graphic EQ to try to null the 92 Hz resonance As can be seen from the composite response curve shown in the 1 3 octave graphic has succeeded only partially in removing the 92 2 resonance while needlessly inserting a the 100 Hz response of the system 5 Parametric In Figure
15. itors transformers etc are referred to as passive AMPLITUDE The voltage level of a signal May be measured volts or decibels Generally corresponds to the volume or intensity of an audio signal BALANCED A 3 wire circuit arrangement in which two conductors are designated as signal lines and and the third is a shield and chassis ground The signal lines are of opposite polarity at any given moment and are of equal potential with respect to ground Balanced input amplifiers are used on all Ashly SC series products to improve hum and noise rejection Jumpering signal minus to ground provides an unbalanced input CENTER FRFNUFNCY frequency or pitch at which a filter is most effective In parametric equalizer it refers to the frequency where a particular boost cut control has maximum effect i A unit by which audio levels be COMPARED Often thoroughly misunderstood are the concepts that decibels represent the level of a signal compared to some reference level 15 dB cut means a certain level less than a previous level the absolute level of the signal need not be known and that decibels are a logarithmic unit Some handy numbers to remember when dealing with decibels 3 dB Double Power 6 dB Double Amplitude Quadruple Power 10 dB 10X Power 20 dB 10X Amplitude 100X Power dBm unit of measurement in decibels where 0 dBm a power level of 1 milliwatt into 600 ohm load
16. lug is wired to the tip to the ring and shield to the sleeve For a mono pee plug combine and shield and connect both to the sleeve An XLR 3 Pin connector is wired to pin 3 to pin 2 and shield to pin 1 Mono Phone Plug unbalanced inputs and outputs nd Tip Sleeve Ring Stereo Phone Plug for balanced in puts and outputs XLR Type Connector Male Shown DISTORTION Generally refers to ANY modification of an audio signal which produces new frequencies which were not in the original Examples are harmonic distortion where a circuit adds overtones to a fundamental signal and intermodulation or IM distortion where two frequencies beat together to _ produce sum and difference frequencies FEEDBACK Generally refers to any process where an output is in some form routed back to an input to establish a loop Negative feedback tends to be be self stabilizing while positive feedback causes instability FILTER A circuit designed to pass some frequencies but not others There are three general categories of filters High pass band pass and low pass The high pass filter passes frequencies above a certain limit the low pass passes frequencies below a limit and the band pass passes one group of frequencies without passing those above or below Our equalizer uses band pass filters crossovers use high and low pass filters FREQUENCY pee og The
17. olume level to purposely induce feedback and then tune to remove it The difference is that the SC 68 has a built limiter which will keep the feedback from running away and maintain it at a listenable level until you have identified the feedback frequency As soon as you have notched out that frequency the SC 68 will automatically increase its gain and find the next trouble spot for you In this way the equalization process can take place at safe listening levels and a relaxed pace As an added feature the meter on the SC 68 will let you see exactly how much you ve improved system headroom leaving no doubt about the effectiveness of the EQ you ve applied In order for the meter reading to be accurate you 1 be asked to Zero the meter at the beginning of the EQ procedure The step by step procedure for room equalization with the SC 59 5 below SET UP PROCEDURE 1 Normal the SC 68 all 8 filters switched OUT Mode switch set to OPERATE FLAT Patch the SC 68 into your system between the mixer and your electronic crossover or between the mixer and power amp if you re not using an active crossover 2 Set up your system for normal operation just as if you weren t using the SC 68 ie play some music through the system and verify that everything is working and sounds reasonable Turn up whatever mic inputs you normally use and adjust each mic s sensitivity and EQ as usual In this way any room EQ you do will
18. out in the same manner As this process continues the built in gain meter indicates directly the improvement in gain before feedback headroom The meter can also be used to show the effect of such factors as aud speaker placenent or movement OT ODJECTS tne stage AS result tuning for minimum feedback becomes a precise process without the speaker damage and ear abuse which often occur with conventional means The Ashly Parametric Notch Filter is capable of much narrower and deeper notches in the audio frequency spectrum than can be achieved with a typical parametric or graphic equalizer Because it exerts its maximum cut at precisely the problem frequency its net effect on the perceived audio response of a system is negligible A B comparison of flat and notched signals sounds identical except for the absence of feedback and musical hot spots Low noise and distortion add to the audio transparency of the SC 68 As powerful and flexible a tool as the SC 68 is it is actually quite easy to use once its functions are understood Please read this manual carefully in order to take full advantage of the SC 68 s capabilities UNPACKING As a part of our system of quality control every Ashly product is carefully inspected before leaving the factory to ensure flawless appearance After unpacking please inspect for any physical damage Save the shipping carton and all packing materials as they were carefully designed to r
19. repetition rate of waveform Frequency is measured in Hertz One Cycle per second cps is one Hertz Hz The higher a note ona musical scale the higher its frequency FREQUENCY RESPONSE Refers to relative gain and loss at various frequencies across the audio band May be illustrated by graph called frequency response plot usually grating decibels vs Hertz or octaves HERTZ Hz The unit of frequency measurement Formerly called Cycles per Second this explains it perfectly HEADROOM Refers to the increase level above normal operating level that can be obtained without clipping Usually expressed in dB 4 IMPEDANCE o Essentially the AC equivalent of resistance It describes the drive Capability of an output or the amount of drive required for an input at any given signal level pe KHz 7 Kilohertz 1 000 Hertz LEVEL a magnitude of a signal expressed in decibels or volts LINE LEVEL JE Er T Meaning somewhere around OdBY as opposed to MIC levet of around 40d8V OCTAVE A logarithmic unit to compare frequencies 1 Octave means double frequency 1 Octave means half frequency 12 DEFINITION OF TERMS AS USED IN THIS MANUAL ACTIVE Electronic circuits which use devices such as transistors and integrated circuits and which are capable of voltage and power gain as well as loss Circuits using only resistors capac
20. s to an immediate frustration because these characteristics are never exactly appropriate What do you do when you need a fader right between two sliders on a graphic In the late sixtys the first parametric equalizers were developed by George Massenburg at ITI Parametrics provide independent and continuous adjustment all three possible characteristics amplitude center frequency and bandwidth As a result virtually any desired frequency response may be obtained with no restrictions imposed by the equalizer itself A parametric notch filter is further distinguished from other equalizers in that its amplitude adjustment is cut only type and it is capable of much more attenuation at the center frequency greater than 30 dB than is a typical parametric equalizer 12 15 dB The SC 68 consists of 8 individual filter circuits which are applied to a common buss Each filter acts as a frequency dependent resistance with the resistance dropping to zero at the center frequency In effect the audio signal is shorted to ground at the center frequency This enables each band to operate as a nearly infinite cut Each filter can be individually switched on and off the buss to test its effect and the entire unit can be bypassed to compare the final setup to a flat setting WHAT CAN THE SC 68 DO THAT A 1 3 OCTAVE GRAPHIC CAN T The adjustable center frequency and extremely narrow bandwidth offered by the SC 68 make it more useful than a
21. should be zereoed at the beginning of the setup procedure See application notes which follow Setup mode filters bypassed Setup controls still active Use this mode for A B comparisons of system gain with and without EQ during setup procedure SPEED control Adjusts the attack and release characteristics of the limiter when the SC 68 is used in the SETUP mode Different feedback frequencies in different size halls take varying amounts of time to establish themselves This control prevents the limiter from hunting and false tracking Figure 7 SC 68 Setup System Controls USING THE SC 68 TO CORRECT FEEDBACK PROBLEMS Most sound system operators are familiar with a method of tuning a room that involves purposely causing feedback to occur by turning up system gain and then equalizing at the feedback frequency to stop the feedback Usually after the feedback has been stopped the operator will again increase system gain until another feedback frequency occurs That frequency is EQ d and the whold process is repeated until it becomes impossible to identify individual predominant trouble spots The problem with this approach is that it s very easy for the feedback to get out of control which can be annoying at best or destructive at worst d The setup estan in the SC 68 essentially uses the same procedure described above to identi fy and remove feedback problems as usual you will turn up your mixer s v
Download Pdf Manuals
Related Search