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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.
Sibilance is a term that usually refers to the hissing effect produced when a vocalist speaks or sings a hard S sound. This S sound can be overwhelming and irritating and could be especially bad when certain singers are recorded with less-than-optimal microphones. Hi-hat cymbals and some other high- frequency instruments can also create sibilance. The challenge to eliminate this unwanted sound is so prominent in the recording world that a specific type of dynamics processor was developed to tackle it, called a de-esser.
In a typical compression or limiting scenario we know that the processor looks for and reacts to a signal's amplitude going over the defined threshold. It doesn't matter if that signal is a low-frequency signal or a high-frequency signal, a bass note or treble note. Any amplitude value measured over the threshold will cause the compressor to react and reduce the gain as prescribed by the ratio, attack, and release controls. But what about special scenarios where we're looking to attenuate the signal only in a certain frequency range? More specifically, what if we want to engage the compression only when the hard S of a vocal is detected, but not anywhere else? That is the main purpose of the de-esser.
Listen to the following example. Listen specifically to how the S's sound in each example. First we have a vocal track without a de-esser on it. Notice the prominent S sound. (Male speaker: There's a girl named Sally who sells seashells.) And now here's the same vocal track with the de-esser engaged. (Male speaker: There's a girl named Sally who sells seashells.) Technically, de-essers are frequency- specific compressors because they're set up to react only to the amplitudes in a specific range of frequencies in a signal, rather than reacting to all the signal's amplitude uniformly.
This frequency-specific compression is achieved by feeding a filtered narrow band of boosted frequencies, generally centered around 6k to 8k, where the S sound lives, into the compressor-detection circuit. This makes the compressor much more sensitive to those frequencies and thus any loud S sounds will breach the compressor's threshold and trigger compression on the signal. This compression can be set to occur over the entire signal, compressing all the frequencies at once, or only over a defined portion of the signal, such as the higher frequencies above 5k.
De-essers generally have two major controls: threshold and target frequency. The threshold works exactly the same as it does on a compressor or a limiter, defining the point at which the de-essing will kick in and reduce the sibilant sound. Set it an appropriate level to reduce the sibilance without drastically affecting the other frequencies on the track. The target frequency determines where the de-esser will look for sibilance in the signal. Set this frequency where the signal is most sibilant and harsh sounding. Your de-esser may have the option to de-ess only the high frequencies on a track.
This option allows the de-esser to be more transparent, as it only reduces the level of the high-frequency material passing through it, leaving the low-frequency material unchanged. De-essers are extremely useful tools because they tame sibilance without having to lower the overall high-frequency content. They could be used on both individual tracks and also entire mixes. While many people think about using them only on vocals, de-essers are indispensable tool in mixing drum tracks that are a little too bright in the wrong areas or when we mastering an entire mix.
The beauty of de-essers is that they're frequency-specific compressors that we can tell to work only when a problem area is detected. Let's dive into an example of de-essing in the next movie.
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