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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.
As we've been discussing dynamic processors and dynamic range, you may have heard me throwing around terms like headroom and gain staging. Headroom is the amount by which the signal-handling capabilities of an audio system can exceed the average working level of the system. Headroom can be thought of as a safety zone, allowing transient audio peaks to exceed this average working range without exceeding the signal capabilities of an audio system--digital clipping, for example. Another way to think about this is to imagine the ceilings in your house.
Unless we're all NBA players, most of us will likely walk around the house just fine without hitting our heads on the ceiling, and depending on the height of your ceilings, there's probably a good two to four extra feet of headroom in case you get excited and want to jump up and down. Headroom in the analog world allows the signal breathing room before the circuit starts to distort. For example, in an analog mixing console, or tape machine, think of headroom as an amplitude range in which the signal's input and output response remains linear, that is, not compressed or distorted.
However, in many cases we like to push the boundaries of this range to introduce harmonic distortion or interesting artifacts that can be quite ear-pleasing. It is important to recognize that unlike analog gear, in digital systems, this gray area range beyond the nominal headroom does not exist. Digital systems remain linear in the response, all the way to the clipping point at 0 dBFS. While tape tube and other analog gear might push back and introduce natural compression to a signal as its headroom is breached into distortion, a digital system will simply clip the signal hard, creating a nasty square wave out of your waveform peaks.
Think of it as the difference between having a soft layer of pillow on your ceiling before reaching hard drywall of concrete. Well in the digital domain there is no pillow, just the hard surface. Gain staging is the term used to refer to the level at which you pass a signal from one part of signal change to another: from plug-in to plug-in, from insert to mix bus, and so on. Cranking up the volume in one processor can leave you without any headroom to move on to your next stage of processing. If I ratchet up a snare's gain in a compressor, throwing the transients up into the extreme end of the DAW's headroom range, and then pass that signal into an EQ and boost 60 dBs on the top end, what do you think happens? Clipping, distortion, and all kinds of nastiness.
Some DAWs and plug-ins utilize higher internal bit-depth processing, like 32 bits or 48 bits that potentially provide additional headroom and avoid clipping. But that additional headroom still can't save your signals from being cut off at the converter at 0 dBFS. Ultimately discussing the dynamic peculiarities of every plug-in, mixer, and piece of outboard is way beyond the scope of this course. Take away from this the simple fact that level matters, and at some point in your mix, there will be a finite amount of dynamic range and headroom that you have to respect.
Digital distortion can be very audible, in which case, you should immediately take action. But digital distortion can also be very subtle, something that adds up track to track, something that creates an indescribable haziness over your work that you might not be able to put your finger on. Manage your levels and I guarantee you, your mix will sound better for it.
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