The speed at which a signal comes and goes as the compressor grabs and releases the program material is controlled by the processor’s attack and release controls. While a compressor’s envelope can be used to shape a signal in creative ways (e.g. make a snare drum punchy or a vocal extra breathy) it can also work against us if used improperly. When first learning to use compressors and limiters, it can be difficult to hear the compressor’s envelope, or attack and release settings, making them difficult if not impossible to set correctly by ear. While there is a certain amount of practice and experience involved with hearing the subtleties of attack and release, especially at low levels of gain reduction, one thing that I find that helps me hear these parameters working is to monitor at lower listening levels.
Our monitoring equipment (speakers and amplifiers), as well as our human auditory system, begin to naturally compress material at very high SPLs (very loud listening levels). While monitoring your mix at extreme levels is not a great idea for a variety of reasons, namely fatigue and hearing loss, it is especially difficult to hear subtle envelopes in your compressor’s attack and release settings when so much gain is competing for your speaker’s (and ear’s) attention. In other words, if your speakers are so loud that your ears and amplifiers are also adding compression to the signal, how can you expect to make critical decisions about compression?
This is not to be confused with discussions over equal loudness contour graphs and the frequency response of our hearing at different SPLs (there is a whole explanation/discussion of that in my Foundations of Audio: EQ and Filters course ). I am talking about the ability to accurately hear subtle gain changes in a signal over fractions of a second. While I might crank up the volume when EQing my bass and kick drum, to take advantage of my ear’s flatter frequency response at higher SPLs, I will work at much lower levels while listening for subtle changes in a signal’s envelope during compression.
Another trick I find useful when trying to get a sense of my compressor’s timing is to initially use deeper threshold and ratio settings, then ease back when I find something that works. Working the compressor harder creates more push and pull and can help you hear the envelope of the gain reduction, because a greater gain change is happening during the attack and release phases.
It is important to note that compressors attack and release cycles (while often labeled in milliseconds) can be radically different from one another, even varying with the type of signal and the amount of gain reduction being performed. In other words, one compressor plug-in with an attack of 10ms may react entirely differently than another compressor set for a 10ms attack, and the same compressor’s envelope may react differently to one instrument versus another. This is why I suggest that instead of trying to acquire and learn every compressor on the planet, you set aside a few “go-to” processors to learn extremely well. This way, you will be able to predict how they will react under different mixing scenarios, allowing you to translate the sound in your head faster.
At the end of the day, manipulating a signal’s envelope using a compressor’s attack and release controls is an entirely subjective task, with one man’s punch and swagger sounding like another man’s unwanted pumping and breathing. The sooner you can clearly hear the envelope working, the sooner you will be in control of your own esthetic, and form your own opinions about which compressors you prefer on specific material.
To learn more about attack and release, as well as other compression and limiting techniques, be sure to check out my course Foundations of Audio: Compressors and Dynamic Processing @ lynda.com