dbx 166 Professional Dynamics Processor Instruction Manual

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ABOUT GATING
Noise reduction The basic purpose of a noise gate is to remove unwanted background sounds in the
spaces between desired fore ground sounds. Note that there has to be some real distance in level between the unwanted and wanted material – at least a few dB — in order for the 166’s gate to “get its foot in the door.~’ If levels are too close (e.g., because of earlier compression, or because the mikes were closer to the unwanted than to the wanted sound), the gating efforts of the 166 will be for naught.
One of the more common uses for a gate is to tighten or “dry up” drum sounds. As with most dynamics processing, it’s ideal if there is a separate mike on each drum and cymbal (or group of cymbals) and each is individually gated. Each mike is auditioned separately and the gate threshold adjusted to eliminate the sound of all but the desired drum. (Hint: start with the threshold very low, so all the sounds come through, then increase it until only the desired drum is left.) It’s likely that you’ll find the Fast release setting best for most drums, while slow usually is better for cymbals and some toms. When things are adjusted correctly, each drum will sound tight, punchy, and dry -detailed and defined.
When you don’t have enough mikes (or 166es!) to cover each drum, then group them: snare and center toms, side toms, bass, cymbals. The idea is to get as close as possible to only one mike on at a time so only one sound is picked up, instead of several.
Another common use for a gate is in vocal recording. Especially after compression, the noises picked up by a mike an inch away from a singer’s mouth can be very obtrusive. Try the 166 in its slow release mode to gate out these noises. Other applications include keeping live drum tracks from “contaminating” ~n acoustic-piano track, and general solving of other sorts of leakage problems.
Changing sound quality There’s more to gating than just keeping out unwanted background noises: you can
use the 166 gates to change sonic character. This is because gates can be used to reduce or otherwise alter the quality of instrumental ambience and reverb. As the sound decays after an instrument stops, its reverberation level will fall through the l 66’s Threshold setting, below which it can be made to die out more or less quickly – in any case faster than the natural sound. Experiment with changing the “tail” of the sound; the fast setting will nearly eliminate reverb.
In other situations, a 166 can be used to prevent or reduce leakage among mikes in sound reinforcement or during panel discussions. Simply set the Threshold control below the level of the music or speech. Similarly, in broadcasting, a 166 can be used to clean up noisy feeds (land lines, ENG audio) if it’s placed at the output. Wind or air-conditioning noise during a remote interview can be controlled as well: proper 166 gate attenuation can keep noise during pauses from being either loud (obtrusive-sounding) or too soft (peculiar-sounding) – or modulated.
The attack time of the 166 gate is short, so the complete transient at the beginning of a sound comes through. We’ve already touched on the differences between the Fast and Slow release rates, but never hesitate to experiment to get the best results for a particular situation.
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ABOUT COMPRESSION
General The purpose of a compressor is to reduce the dynamic range of a program and give
you control over its dynamics. The 166’s Ratio and Threshold controls can produce a wide variety of dynamic-range-reduction effects, from gentle taming of overall dyna.mics to limiting of .peaks to squashing all dynamics.
For example, at low compression ratios, a very low Threshold setting can be used to reduce gently the overall dynamic range of a program. Higher ratios with low thresholds will provide leveling for instruments and vocals. High thresholds generally are used for limiting program levels overall. Ratios of 6:1 and higher effectively prevent outputs levels from much exceeding the threshold (assuming the Output Gain is set to 0).
Note that compression of the entire program (produced by low thresholds) tends to sound less natural at high ratios. Ratios of perhaps 4:1 and lower affect dynamics to a lesser degree, and are often used to tighten up a bass guitar; snare, and vocals. Moderate settings typically are used during mixdowns and for leveling the program in a broadcast.
The l 66’s OverEasy circuit prevents compression at high ratios from sounding too unnatural. This is because as the signal rises above threshold, the ratio changes gradually, from l :1 (no compression) to :that set by the front-panel knob. You can put this feature to especially good use in those situations when you need protection from excessive peak levels but desire gentle compression on most of the program. By setting the threshold at a moderate level and using .a moderately high compression ratio (6:1, l 0:1, etc.), you will provide limiting for signals well above threshold and gentle compression (much less than that set) for signals at or below threshold. See the Over Easy curve, p. 2, to understand how this works.
It’s always useful to watch the gain-reduction LEDs to see the amount of processing taking place. With practice, a glance will confirm what your ears tell you that things are going okay, or that there’s a little too much or too little. Your 166 can achieve desirable effects with proper settings derived from experience; when it’s used too liberally, the unusual results may be suited to special effects only.
Here are some specific situations.
Variations in mike levels As the distance between vocalist and microphone changes, signal levels change.
Start at 2:1 with a low threshold setting to begin to smooth these out. With OverEasy, ratios up to l 0:1 can be used here to good effect.
Variations in instrument levels To achieve smooth electric-bass sound, start at about 4:1. Strings and horns like-
wise benefit, and strings will have their “sustain” increased. Note that large amounts of compression are usually more audible in a mixed stereo program; if the separate tracks were compressed before mixing to create the program, compression is much less noticeable.
Raising the signal out of a mix Since reducing dynamic range can increase the average signal level and meter
readings, a single track can be brought up out of a mix by boosting its level slightly and applying compression. It’s also possible to separate certain vocals and instruments from an already mixed program by using the sidechain; see p. l O.
-8-

Preventin ta saturation A high threshold but below tape saturation) and high compression ratio will cause
the compressor to reduce gain in a controlled manner before the tape overloads and distorts.
Speaker protection and acoustical distribution Compression will keep excessive levels from damaging drivers in sound-reinforce-
ment systems. Limiting also enhances intelligibility by letting low-level material be reproduced throughout the house at higher volumes; in a performance, this increases intimacy, as whispers become clear at virtually every seat. Our OverEasy characteristic permits high amounts of compression (e.g., 10:1) to be used without vocalists or musicians feeling choked back – and with high average levels maintained without speaker damage due to heat buildup in the drivers. As a rule, to give the best protection, your 166 should be as close as possible in the signal path to the power amp. For maximum SPLs, large sound-reinforcement systems frequently have a separate compressor on each output of the electronic crossover(s).
Where the 166 will be expected to allow virtually no level change unless an emergency (wildly excessive levels) arises, set the ratio to Infinity:! and the Threshold to the highest level. OverEasy will never act in the fast, unpleasant manner of a typical “hardknee” compressor, but it will give a measure of real protection. See the next section, too.
ABOUT LIMITING and SOFT. CLIPPING
PeakStop allows you to control the maximum peak levels at the output of the 166 irrespective of any other control. As mentioned, it comes after the compression and other circuitry, including the output gain, so it lets an absolute limit be put on the peakto-peak excursions of the output. PeakStop works instantaneously; you’ll be able to apply moderate amounts of compression and still be independently protected from large transients, other short-term overloads, and broadcast overmodulation.
PeakStop consists of a sophisticated voltage-controlled clipper that produces a minimum of audible distortion. It rounds the corners of a peak rather than cutting it off sharply, as the term “clipping” implies. By making a signal’s leading and trailing edges curves instead of sharp corners, it reduces the amount of higher-order, offensive-sounding harmonics that conventional clipping causes. The level at which PeakStop is activated is adjustable from Oto +20 dBv. Note that small signal excursions above the set value of PeakStop are possible, to allow the rounding to take place. Therefore, for any applications where you must not exceed a given ceiling, set the PeakStop control 1-2 dB below it to be sure.
The PeakStop LED flashes whenever peaks attempt to exceed the PeakStop level and get reduced in amplitude. To disable the function altogether, simply set the control to +20 (which is the maximum output level of the 166 anyway).
In use, the PeakStop function can prevent an amplifier from being driven into hard clipping, where it may lose control over the speaker system. PeakStop is a smooth, wellcontrolled clipper whose behavior is sonically similar to the gentleness of OverEasy compression; its clipping is much preferable to a power amp’s. As noted, control of speaker overexcursion, of broadcast overmodulation, and of harsh electronics clipping are all applications; with PeakStop and OverEasy ·, you have the best of both worlds: virtually inaudible rms compression and peak protection downstream, at the end.
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Normally, the control is set to just under the peak clipping level of the equipment downstream. This way, clipping will be softer and controlled within the 166. The LED should light occasionally, on peaks only; if the LED lights often, of course, reduce the compression threshold and/or increase the ratio, to allow less peak signal level at the output.
SIDECHAIN APPLICATIONS
In all the following situations, it’s the Sidechain Monitor function that will save you time and trouble, letting you adjust the preceding processor(s) and instantly confirm that things are (or aren’t) going the way you want them to.
General hints It’s possible to separate certain vocals and instruments from a mix by making the
compression fre uenc -sensitive. With an equalizer inserted into the Sidechain input (but not in the audio path, the EQ settings do not shift the timbre or equalize the audio signal; they merely alter the threshold of the compressor as a function of frequency.
In such an arrangement, frequencies that are boosted on the equalizer will be suppressed in the audio signal. The converse may also be used, of course: dipping the equalizer on a particular band prevents any sound with dominant energy in the affected register from compressing so much, because the 166 will detect less need for compression.
For example, if you want to suppress an overly loud bass drum, boost the equalizer’s response below about 150 Hz. This will make the compressor reduce gain whenever energy in this region is detected. Furthermore, raising the threshold will cause this to happen only on very loud kicks. To put it generally, a relatively high threshold setting can prevent most sounds from being affected while solo and very loud sounds within that frequency range are held back. (Of course, when compression does occur, the entire program level is affected.) Depending again on the threshold setting, frequencies outside that range will not cause compression.
During the recording of cymbals and toms, a compressor with an EQ in the sidechain path can help prevent tape saturation. The equalizer can be adjusted for a boost peaking at about 5 kHz, causing the cymbal to be compressed on a very loud crash and stopping saturation of the tape at higher frequencies, where there’s less headroom. However, gentle tapping with a stick or cymbal brushing will not be held back. And the tomtom likewise, being a lower- frequency instrument and better-tolerated by the tape, has less need for compression. EQ in the sidechain circ .uit can make the compressor not as readily triggered by a loud tom-tom beat as by an equally loud cymbal crash.
De-essing In the absence of a de-esser, small amounts of high-frequency (6-10 kHz) boost in
the sidechain path frequently will help in the processing of vocals that may have been brightly equalized beforehand or that suffer from prominent sibilance (“ess” sounds).
Speaker protection If a ·single compressor is to be used with a multi-way speaker system (after EQ,
before the crossover), you are faced with the problem of keeping the entire system level down below the point of destruction of the most sensitive component. If midranges are frequently blown, for example, the whole system must be run at a lower SPL or additional mids must be added. By the insertion of an equalizer in the sidechain of the 166, it can be made sensitive to the frequencies the midranges handle, permitting the entire PA system to be run at higher average levels and dropped back only when damaging signals are present.
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Broadcasting A preemphasis filter network pla c ed in the sidechain of a 166 proces sing preemph-
asized audio permits higher average signal levels to be run within the headroom limit s of the broadcast chain.
Filtering Narrow-band (“notch”) filtering for rumble, feedback, equipment noise (e.g.,
cameras) may be put in the sidechain to make the compressor less sensitive to such problems.

Anticipatory compression If you feed the program directly into the sidechain and send the audio signal
through a delay before the 166 audio input, the 166 can “anticipate” the need for gain change. With experimentation, the effect can become that of “zero” atta c k time at a
given frequency. Additional delay beyond this “zero” time will then cause the co mpressor to finish reducing the gain before the leading edge of the loud passage even enters the 166, which will cause the program material preceding the loud pass a ge to be suppressed. The 166 will then begin to recover from compression (it will release, in
other words) before the loud passage has dropped back down toward the set threshold. This will cause the output level to surge as the note(s) should be decaying. Suc h a spe c ial
effect sounds similar to the dynamic-envelope inversion you may be fa miliar with fr om
reverse tape playback. See diagram.

SOURCE

DELAY

166
AUDIO INPUT AUDIO
OUTPUT SIDECHAIN
INPUT

OUTPUT

Keyed gating

Controlling the gating of one signal by another perm its perfe c tly in- sync h pla yin g

and overdubbing among individual instruments or precise soni c a ugmentation – “fa tten-

ing” – of a weak solo. An example of the former would be synchroni z ing bass guitar an d

drum; an example of the latter would be using the drum signal to key an oscillat or which

is set an an appropriate frequency to “tune” and “punch up” the drum sound. See dia gram.

As noted, the Release Rate switch is helpful for determining the sound of the final

produ c t.

:,o 1-1z-vARv To
“TI.M” DA.M OR BASS GUITAR

166

0__; osc
“WF.AK”
I( ICK-oR.M TRACK

AUDIO INPUT AUDIO
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INPUT

MIXER
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‘FAr I( ICK-oR.M
TRACK OR KICK-oR.M TRACKWITH
SYNCI-ED BASS

Selective gating You can also do frequency-sensitive gatin g, letting you tune t he re sponse of the
gating action. If you’re gating a kick drum, for example, in a tr ack with lots of le a kag e, you c an tune in to the frequency of the kic k with an EQ and the gat e will respond only t o
the drum. Again, see diagram below.

166

SOURCE

AUOIO

INPUT AUDIO

OUTPUT

EO

SIDECHAIN INPUT

OUTPUT

FILTER Tu-El TO KICK-oR.M
FRE0..ENCY

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STEREO DYNAMICS PROCESSING Stereo coupling is useful for all applications where two channels must be com-
pressed and the left /right perspective must remain the same. Examples include the L and R overhead mikes on a drum kit or piano, a stereo submix of a vocal ensemble, the feed from an X-Y or other pair of mikes in a classical recording, a complete stereo mix, etc. All of our earlier comments about compression and gating apply here; the difference is that when the Stereo Couple switch is pushed, the gain changes in the two channels will be identical.
In this mode, the signals at each rms detector are combined (so the true rms sum can be sensed) and controlled. As mentioned, all functions of Channel 1 control both channels except for Sidechain and Bypass.
Use this mode whenever imaging must remain stable. NOTES
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I .

WARR ANTY and FACTORY SER VICE All dbx products are covered by a limited warranty (warranties for produ c ts pur-
chased outside the USA are valid only in the country of purchase and the USA). For details, consult your warranty /registration card or your dealer /distributor.
dbx Customer Service will help you use your new product. For answers to que stions and information beyond what’s in this manual, write to:
dbx 1525 Alvarado Street San Leandro, CA 94577 Att: Customer Service
‘
You may call 415/351-3500 between 9:30 and 4:30 Pacific time (USA). The Facsimile No. is 415/351-0500.
Should problems arise, consult your dealer or distributor. If it becomes necesary to have your equipment serviced at the factory, repack the unit, including a note with a description of the problem, your name, address, and phone, and the date of purchase, and send the unit freight prepaid to the above street address, marking it Attn: Repair s.
– 15-

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