dbx 160X Instruction Manual

INC.

The dbx Model 160X is a professional single channel compressor/limiter that features an exclusive combination of the dbx Over Easy and ''hard knee'' compression characteristics. dbx . Over Easy compression permits extremely smooth, almost inaudible transitions into compression due to the gradual change of compression ratio around the threshold. The 160X offers the user the choice of using the Over Easy curve or a mathematically precise "hard" threshold-at any compression ratio selected . The 0'!er Easy curve, coupled with dbx's true-RMS level detector, wide-range Blackmer voltage-controlled amplifier (VCA) and feed- forward circuitry, makes it possible to achieve large amounts of compression without adverse audible side effects. These features also allow the 160X to actually be set for INFINITY+™ compression . This is a special negative compression effect whereby the program dynamics are inverted above the set threshold (i.e., the higher the input level, the lower the output level). The detectors of two Model 160X's can be coupled so that stereo programs are compressed with stable imaging, by means of a simple patch cable between the two units . The stereo coupling can be disengaged instantly by a front panel pushbutton . Program-dependent attack and release times assure natural sound without the need for con- tinuous manual adjustmenu. Threshold and compression ratios are adjustable over a wide range, so virtually any line level signal can be processed effectively. Output gain is also adjustable over a very wide range (±20 dB). These features make the Model 160X compatible with the operating levels of virtually all professional sound and creat ive audio equipment. For metering , the 1 GOX provides a true A MS dua l wide-range LED array which simultaneously shows the an1ount of gain reduct ion up to 40 dB• and the input or output level from -40 dB to +20 dB, depending on the setting of a front panel switch . The 160X also features a true ' 'hard-wi red by - pass" switch , separate detector inputs , Tip/ A ing/ Slec:vc phone jacks as .well as barrier strip con- nectors, balanced active inputs and +24 dBm single-ended output drive capability which can be field-modified to provide transformer or active bal;inced operation . The dbx Model 160X is well suited to a broad ranf)c of applications including tape recording , disc master ing, radio and TV production and bro;idcast , live concert sound reinforcement, mobile and theatrical production . • Th~ I r.nx is c11p•bl~ of gr••t~ r th•n 60 dB of comp,.u ion. IMPORTANT FOR UK USERS The wires in this mains lead are colored in accordance with the following code: Blue: Neutral Brown: Live As the colon of the wir• in the mains lead of this .epparatus may not correspond with the colored markings identifying the terminals in your plug, proceed as follows: The wire that is colored blue must be connected to the terminal that is marked with the letter N or colored black; The wire that is colored brown must be connected to the terminal that is marked with the letter L or colored red. Ensure that all terminals are securely tightened and that there art no . loose strands of wire. WARNING This unit must be protected by a 3-amp fuse, preferably using a fused plug. Also, do not remove the cover without first disconnecting the unit from the mains supply.

dbx • • . .................... _ -----······ ······--· ............ --- 1B0X t S I --- • C D E F Q H I Fif. 1·1 - Model 110X Fro,,t Panel A. BYPASS SWITCH ANO INDICATOR Depressing the BYPASS button creates a "hard-wire bypass" of the 160X's circuitry by connecting the input directly to the output; the LED above the switch turns ON in Bypass mode. B. SLAVE SWITCH ANO INDICATOR Depressing the SLAVE button on one 160X of a stereo pair determines that the other 160X will be the Master (the controlling unit). The LED above the SLAVE button turns ON when the 160X is in SLAVE mode, indicating that the front panel functions (with the exception of BYPASS and DISPLAY select switches) are deactivated and under control of the Master 160X. When neither 160X is in SLAVE mode, each will operate normally as a mono compressor/limiter. C. THRESHOLD CONTROL Adjusting this knob sets the threshold of compression from -40 dBm (7 .8 mV) to 20 dBm (7.8 V). In hard-knee compression mode, the thres• hold is defined as that point above which the out• put level no longer changes on a 1 : 1 basis with changes in the input level. In Over Easy mode, the threshold of compression is defined as the approximate middle of the Over Easy threshold region, as shown in Figure 3-1. 2 0. OVER EASY SWITCH Depres.sing this button changes the threshold mode to dbx's Over Easy characteristic. and allows the middle (an1ber) T~~RESl-iOLO LED to turn ON w: 1P.11 thP. signal is in the Over Easy region. When th is button is out , the 160X oµerates as a hard- k1 ice c:on1pressor /I imiter. E. THRESHOLD INDICATORS These three LEDs indicate the relationship of the input signal level to the threshold of com- prc~sion. The green "BE LOW" LED is ON when the signal is below threshold and the red "ABOVE" l[ D is ON when the signal is above threshold. When the 160X is switched to Over Easy mode, the amber LED is ON when the signal is in the Over Easy region (Ref er to Figure 3-1 ) . F. COMPRESSION RATIO CONTROL Rotating this control in a clockwise direction increases the maximum amount of compression from 1: 1 (no compression) up to infinity : 1 (no increase in RMS output regardless of input level increases above threshold); further clockwise rotation increases compression into the INFINITY+ region, up to• maximum of-1:1 (i.e., 1 1 dB d«reast1 in input level causes a 1 dB increase in output level). In the INFINITY+ region, the 160X inverts the program dynamics for special effects. G. OUTPUT GAIN CONTROL Adjusting this control varies the amount of fixed gain (up to ±20 dB) in the 160X's output amplifier stage. The OUTPUT GAi N control does not interact with the threshold of compression. H. DISPLAY FUNCTION SWITCH AND INDICATORS · Depressing this button causes the upper LEO array to display the INPUT level to the 160X. With the button out, the OUTPUT signal level is displayed. A pair of LEDs immediately above the OISPLA Y switch indicates the selected display • status. I. LEVEL ANO GAIN REDUCTION DISPLAYS The upper row of 19 LEDs displays either the INPUT or OUTPUT level, as selected with the DISPLAY switch. This display is factory set so that 0 dB is equivalent to +4 dBm input or output levf:I ( 1.23 V rms), but may be reset with the rear panel METER CALIBRATION trimmer. (See Section 3.5 for recalibration instructions.) The lower row of 12 LEDs displays up to 40 dB of GAIN REDUCTION being caused by the 160X. (Fixed gain changes commanded by the OUTPUT GAi N control are not displayed by the gain change LEDs but are reflected in the output level display.)

Release Time Output Gain Slew Rate Dynamic Range <2 1 Equivalent Input Noise (unweighted) Frequency ResponM Distortion Below Threshold <> > Distortion Above Threshold <4 > Metering Meter Zero Set Indicators Controls and Switches Connectors Dimensions Wei~t Power Requirements Acc!!ssories Signal input: 60 kO, unbalanced; 100 kO, bllanced. Detector input: 230 kn, unbllanced; 460 kn, balanced. +24 dBm maximum. 22 n, designed to drive 800 0 or greater.• +24 dBm into 600 nor greatar. Variable from -40 to +20 dBm (7.8 mV to 7.8 V RMS). Over E•y: Program-dependent. afflCtld by THRESHOLD, COMPRESSION RATIO settings (COMPRESSION RATIO control determines maximum compression ratio), continuously variable from 1:1 to •:1 to -1 :1. Hard•knee: COMPRESSION RATIO Mttlng defines exact compression ratio. continuously variable from 1:1 to•:1 to-1:1. >60dB Over Easy or hard•knN (switch Alectablet. Program-dependent: 15 ms for 10 dB increae in Input level (above threshold), 5 ms for 20 dB, 3 ms for 30 dB. Program-dependent; varies automatically from 0-600 ms, affected by settings of front panel controls. Variable from -20 to +20 dB. >10 V/us >113 dB <-89 dBm, 20 Hz - 20 kHL +<>, -1dB, 20 Hz - 20 kHz. 2nd harmonic 0.07%; 3rd harmonic 0.07". 2nd harmonic 0.07%; 3rd harmonic o.oa. 19 LEO INPUT or OUTPUT display from -40 to +20 dB, 12 LEO GAIN REDUCTION display from -1 to -40 dB. -15dBm to +10 dBm. BELOW/threshold/ABOVE (grNn, yellow, red),INPUT (red), OUTPUT (red), SLAVE (yellow), BYPASS (red). THRESHOLD, COMPRESSION RATIO, OUTPUT GAIN, DISPLAY function switch, meter zero adjust, BYPASS switch, SLAVE switch, OVER EASY switch. lnput/outpUt: TRS phone jacks and blrrier terminal. Detector: barrier terminal Strapping: TRS phone jack 1·3/4" H x 19" W x 9-1/4" 0 (4.4 cm x 48.3 cm x 18.4 cm). 6.5 lbs (3.0 kg) 115/220 VAC :t: 10%, 50-60 Hz, 8 W AB· 1 active balanced output card. ' (I) Measured in the infinite compres1ion ,~ion of tht thrt1hold curve, tim. required to reduce 1i11nel by 63~ of ltvtl incrtaM (above threshohJl. ' 12) Defined•• tht difference bet-n the maxin1um 1i11nal level end the "A" weighted noiM floor•• mea,ured at the output. (l I l'.1111ured et 1 kHz, 0 dBm input and output . 1• 1 F,gures are typical at infinite comprnsio11. 1 kHz, 0 dBm input and output - 2nd harmonic is relatively unaffected by compression ratiti , time constant, end freQuency, while 3rd harmonic decretMI with llower time con1111nta, higher frequencies ind lower compression rauos . 0 Tran1fo,,,,., for i1ol•r«I floating output •11•ilabl• dirat:tly from: Jl!111t!n Tr•n1form,r,, 10135 Burbank 8l11d., North Hollywood, CA 91601. (SH s«tion 2.3.4.J

This control sets the amount of fixed gain in the 160X's output stage over a range of ±20 dB. Fixed gain added or subtracted by the OUTPUT control from signal passing through the 160X is not affected by the setting of the THRESHOLD control. Gain changes brought about when the input signal exceeds the THRESHOLD reference sett ing ·are in addition to those ·caused by the OUTPUT control. ,3.2 THRESHOLD CONTROL In hard-knee mode this control sets a reference level above which input signals will be processed by the 160X's gain change circuitry in the manner defined by the setting of the RATIO control. Input signals which fall below this level will pass through the 160X unprocessed (except for fixed gain changes directed by the OUTPUT control) . In Over Easy mode, signals begin to gradually activate the 160X's gain change circuitry as they approach the THRESHOLD reference level and they do not get fully processed in the manner defined by the RATIO control until they have passed somewhat above the THRESHOLD • 20 . ·~ - • I(\ } r!t ~ ..., ' ~ 1 1;: I .., . J • " • · I - -- Rro - (\ . . .. - ' • 0 I • I (1 ~ I ..... ,.,_, .... •: t ~ __ ,._ <, Oe!o .. """_'' ... '°'_'_' ____ .__. • 20 • 15 • 1!> - IC • 5 (J • 5 • 10 • I!, • 20 INl"\IT I.( 1/[ L 11181 - • ,c QI /. ~ ,.1 - RED _, • 5 w Abowc 1h,.-d,,Jld '.• 20: 1 ... .., 0 .. ::, •:1 ~ . 5 .. ::, Rot•IIOII Po,nl Th,tshold 0 10 - 15 Btlow thttshold - 15 - 10 - 5 0 • 5 • 10 • 15 • 20 INPUl LEVEL td 81 Fig. 3-1 - Over Env va. Hard•K"" Compreaion reference level. In Over Easy mode there is no distinct point at which processing begins, and the THRESHOLD setting corresponds to a point on the input/output transfer curve midway between the onset of processing and that point at which the transfer curve corresponds to the setting of the RATIO control (Figure ~1). NOTE: The THRESHOLD setting relates to the signal level seen by the DETECTOR input. In normal operation. the program signal input is connected directly to the detector input. If this is not the case, the signal actually present at the detector input will determine whether and how the 160X processes the signal coming into its SIGNAL INPUT. . . 3.3, RATIO ,C.ONTROL When an input signal is above the THRESHOLD reference level, the setting of this control determines the number of dB by which the input signal must change in level to produce a 1 dB increase in the signal level at the output of the 160X. A setting of 2: 1 indicates an input:output ratio where in a 2 dB increase in input signal (above threshold) will produce a 1 dB increase in output signal. A setting of oo: 1 indicates that an infinite increase in input level would be required to raise the output level by 1 dB. . . The 160X's RATIO control covers the entire range from 1: 1 to oo: 1 and, in addition, goes to Infinity+ (negative) ratios. At a setting of -1 : 1, the above threshold input signal must decrease hy 1 dB in level to increase the signal at the output of the 160X by 1 dB. The control curve of the RATIO potentiometer has been designed to provide total operator control, with scale expansion at the subtle lower ratios for easy, repeatable settings. • 20 • 15 ci • 10 '0 -... • 5 ... > ... 0 ... .. :, ~ -5 .. :, 0 - 10 • 15 . , 1 e,1 \ / 101 Fig. 3·28 - Ratio Con1,01 ~.1, , •. ,- I x,1 -a,, ,,, -1,1 COMl9A • aa10N RATIO \h,tshold _, -1 :1 - 15 - 10 - 5 0 • 5 • 10 • 15 • 20 INPUT LEVEL tOBI Fit- 3-2A - Typical Trllltfer Cwrv• Fis- 3-2 - Ratio 11

Two channels of program material do not necessarily constitute a stereo program. A stereo program is one where the two channels are recorded and/or mixed to create the illusion of a sir)gle, unified "panorama" of sound. The stability of the psychoacoustic "image'' of each sound source within the stereo program depends upon·its ability to maintain a specific phase and amplitude relationship from left to right channel. If two independent compressors are used to process the stereo program, a loud sound occurring in one channel will cause a gain reduction only in that channel. This gain reduction would cause the perceived image of any sound spread between the two channels to move toward the side which had not been compressed, because the spread signal would be momentarily softer in the compressed channel. This can be avoided by linking the two compressors in such a way that both channels receive the same amount of compression - an amount equal to the maximum ''needed'' by either channel at that moment. On the 160X, this is accomplished by means of the STRAPPING jacks; a cable between these jacks permits the RMS detectors of both -units to "talk" to one another - but only when one of the units' SLAVE buttons is depressed. Each compressor then senses the incoming signal level, which is compared to the threshold set on the master (the unit whose SLAVE button is not depressed). If the comprealon Is ;equired by either channel, both channels are a,bject to compression - the same amount of it - so the stereo image remains stable. When compressing a stereo program with a pair of 160Xs, only the master unit controls need be adjusted. 12 3.5 METER CALIBRATION The INPUT/OUTPUT LEVEL DISPLAY in thr 160X is factory.calibrated to indicate "O" when the signal level is +4 dBm (1.23 V) at either the input or output of the 180X, depending on the DISPLAY function switch position. (The METER CALIBRATION control does not affect the -GAIN CHANGE LEDs.) ·. To recalibrate the LEVEL DISPLAY, depress the DISPLAY button to meter the INPUT LEVEL, and feed a 1 kHz signal at the selected nominal operating level (the level desired for a ''O dB" meter indication) to the 180X's SIGNAL INPUT. Then adjust the rear panel METER CALIBRA- TION control until the meter indicates ''O dB."

4.1 SMOOTHING VARIATIONS IN VOCAL LEVEL When the distance between a vocalist and a microphone changes, variations in signal level occur. Start with the 160X adjusted for low compression (around 2:1) and adjust the THRESHOLD control for optimum results, then increase RATIO if necessary. . . 4.2 SMOOTHING VARIATIONS IN INSTRUMENT LEVEL To achieve a smoother electric-bass sound, compress the instrument's output with a ratio of about 4: 1. Compression lessens the loudness variations among the strings and increases the sustain. Other instruments, such as horns, vary in loudness depending on the note being played,and benefit similarly. NOTE: When compressing a stereo program with a pair of 160Xs, the factors affecting a compression curve, and the actual compression and threshold settings, are like those previously covered with reference to single channels of program material. However, it will generally be found that large amounts of compression are more audible in a mixed stereo program than they might be on the separate tracks that were mixed to create the program. 4.3 RAISING A SIGNAL OUT OF A MIX Since reducing dynamic range increases the average signal level and meter readings by a small amount, a single track can be raised out of a mix by boosting its level slightly and applying com- pression. It is also possible to separate certain vocals or instruments from a mono program already mixed by following the procedure in Section 4.6.1. 4.4 PREVENTING TAPE SATURATION With programs of widely varying levels, com• pression can prevent recording levels from satur• ating tape tracks (see also Section 4. 7 .1). 4.5 SPEAKER PROTECTION Compressors are frequently used to prevent excessive program levels from damaging drivers in a sound-reinforcement system. Limiting also benefits intelligibility by allowing low-level input signals to be reproduced through·the system at higher volume. In a musical performance, this provides additional intimacy as the vocalist's whispers are heard clearly at each seat in the house. The Over Easy curve utilized by the 160X permits a very high amount of compression (10:1 or greater) to be used in many situations. Vocalists and musicians don't get the sense of being "choked back", but high average levels can be maintained without the speaker damage which would norn,ally occur due to excessive heat buildup in the drivers. In circumstances where the 160X is expected to cause no change in gain unless an emergency arises (wildly excessive levels) some operators set the RATIO to•: 1, the THRESHOLD to the highest permissible level, and operate the unit in hard-knee mode. (In hard-knee mode, the 160X will perform in the manner of Its predecessor, the 16Q.) As a general rule, the comprnaors should be as clou to th11 •mplifi11r, • p0$$ibl• in the signal chain. If the 180X Is placed before the EQ, for example, 1 potentially damaging boost in EQ won't bG seen by the unit and the speakers may be damaged. (See Section 4.8.2.) For maximum sound-pressure levels, large sound-reinforcement systems frequently use a separate compressor on each output of the electronic crossover(s). For a stereo sounckeinforcement system, stereo strapping cabin should be run between the 160Xs in each band (low-low,.mid-mid,.etc) • • 4.8 INFINITY+T~ COMPRESSION . It has been noted that with a full-scale Infinity+ setting of-1.1, a 1 dB decreasa of input level above THRESHOLD causes a 1 dB incmnt1 of output level. It can be seen how this differs from the full counter- clockwise setting of 1 : 1, where the transfer function is linear (e.g., a 1 dB increas11 of input level causes a 1 dB decrease of output level). A total dynamic reversal of the entire program being processed will not occur unless the THRESHOLD is set very low (e.g., -40 dBm) and all the program material falls above the threshold level. More often, some of the program input will be below threshold, and will therefore have normal dynamics - that is, the output level will change linearly with changes of input level. As the input level rises above threshold, however, the output level will begin to decrease. The audible results will differ with different types of program material and different settings. With instruments havina_fast attack times, such as a picked guitar, a harpsichord, or a drum, a low threshold will all but eliminate the attack transient. Interesting effects can be obtained by setting a moderate threshold with instruments with a slower attack, such as wind instruments or bowed strings; the level will build normally up to the threshold, then begin going lower, the output will become very quiet as the instrument is generating its loudest sound, perhaps quieter than when the note first began. 4.7 USING THE DETECTOR INPUT 4.7. 1 Detector EQ For Signal Enchancement It is possible to separate certain vocals and instruments from a mix by frequency-weighted compression. With an equalizer ioserted ahead of the detector input (but not in the audio path), the equalization settings do not shift the timbre or frequency response of the audio signal. They merely alter the threshold response of the com- 13

basis (see Figure 4-1). With this arrangement, raising certain frequencies on the equalizer causes them to be suppressed in the audio signal. A relatively high threshold setting can allow normal sounds t~ be una~fected while solo and very loud sounds are held back. (Of course, when compression does occur, the level of the entire program is affected.) Depen.ding on the threshold setting, lower-level fundamentals or harmonics will not cause com- pression, and the program is not subject to the phase shift normally caused by program equalization. · 10 .. NffCTOR IOUflCI ., .. AUDIO OUT -- leOJI Fig. 4•1 - EQ In DetKtor Padl The converse of the above EQ technique may also be used; dipping the equalizer bands causes any sound with dominant energy in the affected register to pull the level up because the 160X will detect less need for compression. During the recording of cymbals and tom-toms, a compressor with an equalizer in the detector path can help prevent tape saturation. The equalizer can be adjusted for boost with a peak of about 5 kHz. causing the cymbal to be compressed on a very loud crash, stopping tape saturation at high frequencies where there is less headroom. However, gentle tapping of a drumstick or brushing of the cymbal will not be held back. Assuming the tom- tom is a lower-frequency instrument and can be better tolerated by the tape, it has less need for compression. The equalization in the detector circuit means that the compressor is not triggered as readily by a loud tom-tom beat as by an equally loud cymbal crash. 14 In the absence of a more sophisticated de-esser, small amounts of high-frequency boost in the detector path can frequently help in the processing of vocals which have been very brightly equaHzed or which suffer from a prominent "ess" sound. . 4. 7 .2 Detector EQ For Speaker Protection If a single compressor is to be used with a multi- way speaker system (i.e.,before the crossover, after EQ), the system operator is faced with the problem of keeping the entire system level down below the point of destruction of the most sensitive com- ponent. If. for example, mid-range drivers are frequently damaged, the whole system must be operated at a lower sound pressure level or additional mid-range driven must be added. By inserting an equalizer in the detector path of the 160X, it can be made more unsitive to frequencies in the range handled by the sensitive drivers. The system can then be run at higher average levels and will only be dropped back when damaging signals are present. 4.7.3 Detector EQ For Broadcast By inserting a pre-emphasis filter network in the detector path of a 160X processing pre-emphasized audio, higher average signal levels can be run within the headroom limitations of the broadcast chain. 4. 7 .4 Anticipatory Compression By feeding the program directly to the 160X's detector input and sending the audio signal through a delay line before the audio input, the unit can "anticipate" the need for a gain change; see Figure 4-2. With some experimentation, the effect can be that of "zero" attack time at a given frequency. Additional signal delays beyond this ''zero" time will then cause the compressor to finish reducing the gain before the leading edge of the loud passage even enters the .signal input. This will suppress the program material preceeding the loud passage. The 160X will then begin to recover from compression (release) before the loud passage has dropped back down toward the set threshold. This will cause the output level to surge higher as the note or passage should be decaying. This special effect obtained with time delay sounds similar to the inversion of dynamic envelopes produced during reverse playback of a tape recording. When coupled with Infinity+ compression, highly unusual effects can be achieved. IN OfTECTOft j .... IOUIICE ......_ I DILAY IN AUDIO OUT .... leOJI Fit- 4-2 - Deley In Sitnal Path