Fostex 3070 User's Manual
Contents
1. When the DETECT LIMIT LED reference 10 flashes the maximum gain reduction will be 32dB 4 ATTACK The signal level of the compressor is controlled by an inter nal Voltage Control Amplifier The response time of that VCA is determined by this rotary control which is continuously variable from 0 2 through 20 msec 5 RELEASE The amount of time it takes the control circuit to recover from processing and return to unity gain is determined by set ting this continuously variable rotary control from 50 msec through 2 sec 6 INPUT Due to unique design efficiencies this rotary control per forms two functions simultaneously While the threshold level at the input of the VCA detect circuit is fixed at about 18dBV 0 13V by varying the input level you effectively vary the threshold level The total amount of gain reduction is deter mined by the setting of the compression ratio slope and this input level control At a nominal 10dBV line level reference the threshold is obtained with the INPUT knob at scale 3 4 and most of the audio signal is passing unprocessed linear response See Figure 1 1048 OUTPUT f gt INPUT 10dB Fig 1 With the compressor ratio slope set at 1 it is likely that the detect limit LED will light indicating 32dB of gain reduc tion It should be noted that this LED does not indicate over load of the audio signal there is an additional 32dB of system headroom before the co2. 8V Gain 30 B Comp Limit Ratio 1 1 inf 1 Variable comp ratio Max Limiting Attack time Release Time Frequency Response T H D Signal to Noise Ratio Slew Rate Power Requirements Dimensions Weight 32dB from threshold level when Inf 1 0 2 20 msec continuously variable 50 msec 2 sec continuously variable 20 Hz 20 KHz 1 dB Less than 0 03 below threshold Less than 0 1 with 20 dB limiting 80 dB unwt d ref to threshold level 82 dB wtd ref to threshold level l0v usec 120V AC 60 Hz 12W U S A Canadian models 220V AC 50 Hz 12W European models 240V AC 50 Hz 12W UK Australian models 100 120 220 240V AC 50 60 Hz General export models 17 W x 1 3 4 H x 8 1 4 D 430 W x 44 H x 210 0 Net 6 1 21bs 2 9Kg 7 1 4Ibs 3 3Kq 10W Shipping Specifications subject to change without notice 3608 2 4 2005 2sec THRESHOLD ADJ EXP GATE Low PASS FILTER DETECT LIMIT 13246 24 dB 16 dB 2 2 LEVEL DETECTOR gt REDUCTION and LEO DRIVER 4 24 2 LINK DUAL STEREO MONO 2 OTHER NOTE ONE OF TWO CHANNEL INPUT CHANNELS SHOWN 15 Fostex FOSTEX CORPORATION 512 Miyazawa cho Akishima Tokyo Japan FOSTEX CORPORATION OF AMERICA 15431 Blackburn Ave Norwalk CA 90650 U S A PRINTED IN
3. JAPAN 1982 8288 0480 00
4. compressor to handle noisy gui tar or keyboard amps Set the gate threshold level so that when no signal is present the channel is off thereby eliminating FOSTEX 2 KD lt QUI CASSETTE DECK SO FOSTEX 3070 ee 109000000 1000000 1 2 TRACK RECORDER COMPRESSOR LIMITER FOSTEX AB FOSTEX A2 FOSTEX 350 oer Tm 57 so B ollel cliol a 10101019 o 9090 oa 8 TRACK RECORDER FOSTEX 3070 COMPRESSOR LIMITER CASSETTE DECK Typical uses of link mode to preserve original stereo imaging Fig 8 the amplifier noise Then set the compression ratio and attack such that as soon as the instrument is played the level of both noise and signal is raised to the point where normal masking effects take place and the signal predominates In short overall system noise as well as specific noise problems can be efficiently reduced and effectively eliminated by the 3070 8 Creative Effects One of the fun aspects of the 3070 is this accessibility to the detect circuit which controls the VCA You may have had the creative urge to equalize the signal before compression Now 13 you ll be able to experiment by using the equalizer to trigger the compressor so that only selected frequencies for example are process
5. Model 3070 COMPRESSOR LIMITER wners Manual TABLE OF CONTENTS 1 LOCATION OF CONTROLS Front panel 2 2 LOCATION OF CONNECTIONS Rear panel 5 3 INTRODUCTION 6 4 OPERATION 7 5 APPLICATION NOTES 443435 BRE ERR ROSE A E oso ea a e n PR 11 6 SPECIFICATIONS BLOCK DIAGRAM 14 SAFETY INSTRUCTIONS WARNING 10 Cleaning The appliance should be cleaned only as BEFORE OPERATING recommended by the manufacturer Read Instructions Al the safety and operating instruc tions should be read before the appliance is operated Retain Instructions The safety and operating instruc tions should be retained for future reference Heed Warnings All warnings on the appliance and in ihe operating instructions should be adhered to Follow Instructions All operating and use instructions should be followed Water and Moisture The appliance should not be used near water for example near bathtub washbowl kitchen sink laundry tub in a wet basement or near swimming etc Ventilation The appliance shouid be situated so that its location or position does not interfere with its proper ven tilation For example the appliance should not be situated on bed sofa rug or similar surface that may block the ventilation openings or placed in a built in
6. atterns as shown in Figure 4 1048 VARIABLE COMP RATIO OUTPUT gt ANPUT 10dB Fig 4 By adjusting attack and release characteristics these typical compression curves can alte ed radically as in Figure 5 below A small mV signal produces the same maximum output level as a large signal fhis effect similar to automatic gain control AGC can be quite useful for live recording and PA applications 10dB OUTPUT INPUT 10dB Fig 5 Expansion is simply the inverse equivalent of compression The algebraic addition of the two curves shown in Fig 6 would be linear 10dB Zone OUTPUT INPUT 10dB A relationship exists between limiting and gating as well although each has its effect at opposite ends of the dynamic range as shown in Figure 7 10dB OUTPUT gt INPUT 10dB Fig 7 In terms of electronics all these concepts are closely related but in terms of application the differences are pro nounced 5 APPLICATION NOTES 1 Attack and Release The attack is the speed with which the gain reduction cir cuitry comes into action The Release is the time it takes the noise reduction circui try to return to its nominal setting after the signal returns to below threshold The setting of these controls will likely have a more audi ble and pronounced effect over the processed signal than for example the compressor ratio control settings The interactive use of attack and re
7. compression and limiting The key is operational flexibility because the program material itself will always be a significant factor in determin ing the ultimate use of the Model 3070 And in this reason the compressor slope attack time and release time are all continuously variable The noise gate function has an independent threshold setting like having another signal processor in the same chassis You can choose between independent 2 channel operation or linked stereo mode where the stronger of the two signals triggers processing thereby preserving original stereo imaging One of the most outstanding features of the Model 3070 is the control element Gain reduction is accomplished by a VCA circuit which is controlled by pulse width modulation By varying the length of time an internal electronic switch is open or closed during each cycle signal energy is reduced without distorting the program You have also an access to the detect circuit which controls the VCA operation rear panel patch points A vocal or instru ment or equalizer etc connected directly to the detect cir cuit turns the Model 3070 into a creative audio tool whose sonic possibilities are limitless 4 OPERATION The following is a simplified explanation of the operating technique behind the 3070 compressor limiter with expander noise gate function With no compression or gain reduction the ratio of input level to output level other parameters being equal
8. damaged Servicing The user should not attempt to service the appliance beyond that described in the operating in structions All other servicing should be referred to qualified service personnel WARNING To avoid possible electric shock hazard do not expose this appliance to rain or moisture There are no user serviceable parts inside Refer servicing to qualified service personnel FRONT PANEL REAR PANEL zt ol MEMO oc 0c00 654321 65 4 3 2 1 1 LOCATION OF CONTROLS Front panel 1 COMP IN OUT This push type switch determines whether the input signal 111 be processed IN or bypass the circuit OUT when this switch is OUT all function controls on the front panel are disabled and the input signal will then appear at the output jacks unaltered 2 EXP GATE When this rotary control is fully there is click action indicating the OFF position As the control is rotated CW the threshold level for the gating function increases accordingly 3 COMP RATIO This rotary control changes the compressor ratio continuously from 1 1 no limiting through 1 hard limiting a refer ence consider two extreme settings A Set to a scale of 2 the change in output level will be ldB for an input signal 2dB higher than the threshold and the 0 LED reference 8 GAIN REDUCTION will be lit B Set to o there will be no change in output level for input signals higher than the threshold
9. ed by the 3070 Another more familiar effect is perhaps best described as vocal punch through where a lead vocal suddenly seems to break through a loud crescendo or a wall of sound By connec ting the vocal mic directly to the detector circuit of the 3070 the vocalist now controls the compression circuit Other signals sub mixes instruments and music can be set to control the VCA for a limitless variety of audio effects And while creativity can be wildly imaginative it can also be very practical Consider the following use of the detector circuit Suppose you want a keyboard to come up in level as soon as the guitar solo ends and who knows when that will be Just patch the guitar to the detector in out and adjust the controls so that you have effectively an automatic cross fade Since this is a novel feature open to infinite creative possibilities we would be genuinely interested in learning about your particular success in using this circuit For that matter if you find a particular sound with the 3070 that you think is great please send us the details and we ll be happy to pass the information along to other people like you who are interested in getting the most out of today s technology 6 SPECIFICATIONS BLOCK DIAGRAM Input Unbal Phono jack and Phone jack Input Impedance 30 Kohms Input Level 30 dBV 30V max Output Unbal Phono jack and Phone jack Output Load Imp 5 Kohms or higher Max Output Level 18 dBV
10. es good microphones and good micro phone technique getting a good vocal recording that pleases both artist and engineer is sometimes very difficult One reason is that vocals usually contain many peaks and transients but maintain relatively low average levels The compressor limiter helps not only to contain the sharp transients but also to raise the average level for a more consistent blend with the music 6 Link Depending on the program material you will probably find that the processing of stereo signals with the 3070 in the dual mono mode UP gives you more control over the final imaging of the stereo effect In the stereo mode DOWN the stronger signal of the stereo pair will trigger the processing as determined by the settings of that channel Among the several uses for this mode are cleaning up 2 track tapes where you want to preserve the original stereo balance and making fail safe cassette copies during mixdown See Figure 8 7 Noise Gate Functions Any open microphone whether on a vocalist or a floor tom adds unnecessary noise when no signal is being passed The in sertion of a noise gate immediately after the mic preamp is a common practice to guard against noise build up This same prin ciple also holds true during mixdown Patch the 3070 to two channels which go in and out of the mix set the threshold levels and you ve just saved yourself four manual fader changes per in out incident Use the noise gate with the
11. installation such as a bookcase or cabinet that may impede the flow of air through the ventilation openings Heat The appliance should be situated away from heat sources such as radiators heat registers stoves or other appliances including amplifiers that produce heat Power Sources The appliance should be connected to a power supply only of the type described in the operating instructions or as marked on the appliance Power Cord Protection Power supply cords should be routed so that they are not likely to be walked on or pinched by items placed upon or against them paying particular attention to cords at plugs convenience recep tacles and the point where they exit from the appliance 11 12 13 14 Nonuse Per ods The power cord of the appliance should be unplugged from the outlet when left unused for a long period of time Object and Liquid Entry Care shouid be taken so that objects do not fall and liquids are not spilled into the enclosure through openings Damage Requiring Service The appliance should be serviced by qualified service personne when A The power supply cord or the plug has been damaged or Objects have fallen or liquid has been spilled into the appliance or C The appliance has been expased to rain or D The appliance does not appear to operate normally or exhibits a marked change in performance or E The appliance has been dropped or the enclosure
12. lease times is immediately apparent so you will know instantly whether you have the effect you want 2 Automatic Blend A common technique for bringing a vocal into an instrumental mix is to fade the mix slightly as the vocal is brought up Usual ly a manual practice is required and sometimes many re takes are necessary to get it right Try the 3070 this way set the level of the music mix just below the threshold level of the 3070 now if the vocal comes in 5 or 10dB hotter the compressor will re duce the gain of the vocal while automatically reducing the level of the music mix 3 Acoustic Piano Sometimes it s hard enough getting the right acoustic piano sound from your mics only to find the dynamics lost in the mix With the 3070 you can accentuate the attack for an effective punchy sound and any natural room sound that lingers after a note stops ringing can be emphasized by the release control setting to amplify the decay This is the principle behind guitar sustain 4 Low Frequency Definition By nature of course low frequencies lack definition But a judicious use of the 3070 can go a long way in separating the kick drum from the bass guitar for example during the mix By using different compression ratios and or different attack re 11 12 lease characteristics you have more control over the inter relationships of the instruments within the low frequency spec trum 5 Vocals Even with trained voic
13. mpressor limiter circuit overloads 7 OUTPUT This rotary control is for adjusting the output level of the processed signal In a nominal scale position of 4 to 5 referenced to 18dBV at the detect circuit input the signal level present at the output jacks will be 10dBV 0 3V 8 GAIN REDUCTION dB This series of five LED s displays the amount of gain reduction in calibrated decibel readings at 0 4 8 16 and 24 These diodes will not light when the COMP switch is in the OUT position 9 EXP GATE This LED lights when the expander noise gate circuit is in use and when the signal present is below the threshold deter mined by the setting of the EXP GATE control 2 when this LED turns off the signal present is above the threshold setting and is being processed accordingly 10 DETECT LIMIT 32dB When this LED lights maximum gain reduction of 32dB has been reached It also indicates that the detect circuit is over loading and can no longer control the operation of the VCA on a one to one basis Please note that there is 32dB more system headroom above the overload point of the detect circuit so this LED does not indicate distortion of the audio signal 11 LINK When this switch is in the DUAL MONO mode UP the front panel controls for each channel will operate independently In the STEREO mode DOWN VCA operation is linked and both channels will be processed together NOTE The VCA will link with EXP GATE cont
14. rols via the detect signal from the channel which is set at the higher threshold level Both controls must be ON for stereo operation of the expander noise gate function if either control is OFF single channel operation results Turn both controls OFF if you do not require this function for stereo processing 12 POWER ON OFF switch for the 3070 with LED power ON indicator 2 LOCATION OF CONNECTIONS Rear panel 1 INPUT Pin jack Input levels here which will raise the gain to threshold level are 1V with the input level control at full CCW position 36dBV 16 mv at full CW position 2 INPUT Phone jack There is a 10dB pad at this jack so it can accept an input signal 10dB higher than the pin jack Thus input levels here which will raise the gain to threshold level are A 10dB 3V with the input level control at fuil CCW position and 26dBV 50 mv at full CW position 3 4 OUTPUTS The pin jack 3 and the phono jack 4 are wired in paral lel 5 6 DETECTOR IN OUT This patch point gives you access to the detect circuit which controls the VCA operation of the compressor limiter circuit By inserting other processors such as equalizers or audio signals themselves such as vocals a limitless variety of creative effects can be produced 7 AC Power Cord 3 INTRODUCTION The Fostex Model 3070 Compressor Limiter Unit is designed for wide applications in the process of
15. would be linear See Figure 2 10dB OUTPUT INPUT 10dB Fig 2 One of the most outstanding features of the 3070 is the control element Gain reduction is accomplished by a VCA circuit which is controlled by pulse width modulation In the VCA circuit there is an electronic switch which opens and closes at a rate of 200KHz By varying the length of time this electronic switch is open or closed during each cycle signal energy is reduced without distorting the program An important benefit of this type of circuit is lower dis tortion Continuous low frequency response especially is much lower in distortion than typical units when the attack time is set fast For this reason you have more latitude in the use of the release control without worrying about gross pumping and breathing effects Finally the detect circuit which controls the VCA operation is externally accessible on the 3070 There really are no rules or theory of operation here you are in the realm of creative audio effects Personal taste is the determining factor With an infinite compression ratio hard limiting results an effect that can sometimes be harsh to the ear because right at the threshold level any more input increase yields no more output level See Figure 3 HARD LIMITING 10dB OUTPUT gt INPUT 10dB Fig 3 In between zero compression and infinite compression is a continuously variable compression ratio with typical response p
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