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In this first installment of the Foundations of Audio series, author Brian Lee White shows how to improve the sound of a mix with compressors, limiters, gates, de-essers, and other dynamic processors. The course explains the fundamentals of sound waves, and amplitude, explores common compressor controls, and shows how to eliminate unwanted noise using gates and expanders. The course also demonstrates best practices in compression and limiting in a variety of audio applications and covers sculpting the attack and decay of individual notes with transient shapers and applying frequency specific dynamics control with multiband compressors. Exercise files accompany the course and include special Get in the Mix session files.
You might think that using the compressor's fastest attack and release times might be the best practice for compressing an audio signal. While sometimes this is true, very fast attack and release times have their own set of potential problems, and you will often hear the compressor's character more apparently using faster settings. Too fast of an attack time can make a signal sound dull and shave off its attack. The difference between a one- millisecond and a five-millisecond attack on a snare drum can be very apparent in the bite of the transient, especially with more aggressive threshold settings.
(music playing) A fast attack can be a positive thing too. A super-fast attack can mellow out a signal's transients so that they don't stick out of a mix. Consider an aggressive pick rake of an over-strummed acoustic guitar. (music playing) A fast attack setting on your compressor can help tame the signal's bite and make it play nice with the other instrumentation.
(music playing) Now let's talk about release times. Fast release settings can be great for bringing out the sustain and drawing out the tail end of notes, words, and breathes. (music playing) But too fast of a release setting on a low-frequency signal can create a nasty distortion as the compressor literally attempts to follow the oscillation of the slower-moving bass frequencies. It is generally a good idea to use release settings of 20 milliseconds or greater on anything containing significant low-frequency material to avoid this artifact.
(music playing) Remember, fast and slow in terms of attack and release is relative to the signal you're processing. A 50-millisecond attack on a vocal or bass may work great but do absolutely nothing on a snare- or bass-drum hit that lasts only 100 milliseconds in total. When in doubt, use your DAW's time ruler to get a sense of how long a note or phrase actually lasts in milliseconds, or how much of a gap between notes you have to work with if you want the compressor to recover between each note or beat.
Compressing eighth notes on the snare at a faster tempo, like 130 BPM, will likely need a faster release time to recover between hits than would a ballad at 60 BPM with the snare drum beats 2 and 4. Adjust settings in smaller increments when working on fast-decaying percussive material. Some engineers even take this time- between-notes concept to the next logical step by timing their attack, and more specifically release, times to the BPM of the song, using the calculation of eighth note at 120 BPM equals 200 milliseconds as a starting point.
While I too like to set my release times to the beat of the tune in certain scenarios, I generally always set my attack and release times by ear, as I have found that most compressors are very signal dependant when it comes to the reaction time and rarely exhibit attack and release performance down to the exact millisecond setting on the knob. Certain compressors feature automatic attack and release controls which adapt and change based on the incoming signal. So for signals with faster envelopes, the compressor will use faster attack and release times, and vice versa.
These types of compressors can be great for transparent dynamic control, as you're less likely to hear the compressor working so hard, grabbing and releasing the signal based on static attack and release values. Be sure to check out your compressor's user's manual. You would be surprised how many features you may be missing out on because you didn't realize they were there. So to recap, here are some general ideas when setting attack and release times. Shorter attack times control transients and plosives, but settings under 1 millisecond can take the bite or brightness out of signals.
Longer attack times allow more of the signals transient to get through. This helps add bite or punch to drums as the transient passes through uncompressed-- 1 to 10 milliseconds on drums or 10 to 50 milliseconds on non-percussive instruments. Shorter release times help inflate or add sustain to signals but can cause breathing or pumping under heavier threshold and ratio settings. They can also lead to distortion on low-frequency content. Longer release times offer less compression artifacts, but compression may not recover fast enough to react to the next unique note or phrase.
Because every signal is unique and every project has a unique tempo, feel, and energy level, learning to set the attack and release controls by ear using the basic behaviors I have outlined will be so much more beneficial to your mixes than trying to find prescribed settings on the web or with presets. Again, think about what you want the signal to do for you in the context of your mix. Punchy, flat, firm, dynamic, what does the song need? I like punchy snare drums as much as the next guy, but they just don't work on every single song I mix.
So I let the song guide my decision process, right down to every attack and release setting, in how they affect the other elements in the mix and the emotional delivery of the music.
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