Mackie Quad Gate/Compressor Owner's Manual - Page 17

Owner's Manual Compressor Artifacts Two uncomplimentary terms often used to describe the sound of a compressor are breathing and pumping. Breathing threshold fixed but increasing the compression ratio, you'll reduce the output level by compressing only the loudest signals. There are no rules for this. Let your ears be your guide, with the meters as a sanity check. Breathing is most noticeable on a solo voice and is often, in fact, the sound of the vocalist breathing. If release time is short, the gain rises quickly during pauses between words, just as the singer takes a breath. The increased gain makes the breath more audible. Hearing a singer taking a breath may not always be desirable or dignified, but at least it's organic. Few recordings are made in an absolutely silent environment, however. Any ambient noise in the room will be boosted when the gain rises, creating an artificial "breathing" sound, perhaps even bringing leakage from the singer's headphones along with it. All compressors exhibit some breathing, but careful adjustment (which includes controlling room acoustics and mic positioning) can minimize it. Pumping Pumping is another compressor artifact. It's more apparent when compressing an overall mix than a single track. One instrument in the mix that's louder than the others will trigger the compressor into action. If that instrument stops playing, even for an instant, the level of the mix will increase noticeably. Each time the dominant instrument starts or stops, it "pumps" the average level of the mix up and down. Compressor settings that work best on full program material generally have very smooth attack and release curves and a slow release time to minimize the pumping effect. Working the Knobs If your signal has peaks up to +15 dB and you want to reduce those peaks to a more manageable +5 dB, you might set the threshold at -5 dB and compress using a gentle 2:1 ratio. Or if you want to use a stiffer ratio, say 6:1, you'd set the threshold at +3 dB. As an exercise, try plotting out a few combinations yourself. Then set up your compressor and listen to the differences. Lowering the threshold while keeping the compression ratio fixed reduces the maximum output level, since you're compressing over a larger portion of the dynamic range of the input signal. By keeping the The Compressor as a Tone Modifier Adjusting the attack and release times of a compressor applied to an instrument can change its timbre by rounding off a sharp attack or stretching out the sustain portion of the note's envelope. It's sort of like having an equalizer with a different parameter. A drum hit can be "stretched out" by applying a long release time, a healthy gain boost, and fairly high compression ratio. Compressing low-frequency program material requires special care. The attack and decay portions of a kick drum are 60 to 80 milliseconds long, but a low-pitched kick has a fundamental frequency of about 40 Hz. This means that only three of four cycles of the kick's fundamental frequency are heard on each hit, much of that being in the decay portion of the envelope. Compressing the drum with a fast attack time and high compression ratio will make more cycles of the attack portion of the drum audible, making its "thump" sound much more pronounced without having to boost low frequency gain with an equalizer. Try this next time you want a kick in the chest. The beater's attack is at a higher frequency (around 1 to 3 kHz), so a moderately-fast attack will let a few cycles of beater through while working on the low "whump." Slowing down the attack lets more of the beater sound pass before being compressed, often allowing you to increase the impact of the kick drum without increasing the level of the track in the mix. Fast attack times that often work well on vocals, work poorly on a bass, because the compressor actually tries to follow the individual cycles of the waveform rather than the envelope of the note. This characteristic can be used as a special effect, but usually it just takes all the life out of a bassy instrument. The Bottom Line A compressor can never be used by the book - not even this one. You need to listen carefully when you make adjustments. By understanding the effect of each of the adjustable parameters, you'll be better able to reach your goal quickly. Owner's Manual 17