De-essing

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In audio processing, De-essing is bandwidth-limited compression intended to reduce or eliminate excess sibilance in sound recordings of the human voice. Excess sibilance can be caused by compression, microphone choice and technique, and even simply a singer's mouth. Sibilance lies in frequencies anywhere between 2 kHz-10 kHz, and as such the compressor's side chain is adjusted to respond only to these frequencies. There are generally three methods of de-essing: split-band, narrow-band, and frequency sensitive.

Split-band: Split-band de-essing generally splits the bandwidth of the signal in two, using low-pass and high-pass filters. The low-pass signal is not processed, but the high-passed signal is compressed as needed to tame the sibilance. Thus, everything above the crossover frequency is compressed.

Narrow-band: Narrow-band de-essing offers an adjustable frequency control and sometimes bandwidth control. The goal is to locate the specific sibilant frequencies using as small a bandwidth as possible and attenuate only those. This leaves frequencies below AND above untouched.

Frequency sensitive: Frequency sensitive de-essing is accomplished by directly altering the side-chain of a compressor. This is accomplished by "multing" (making a copy of) the signal and equalizing one it to contain only the sibilant frequencies, feeding that into an able compressor's side chain. Thus, like a narrow-band de-esser, it's processing is only engaged with specific frequencies. However, the compression itself will apply to the full-bandwidth signal. As such, attack and release times are extremely important, and threshold settings can be not placed as low as with other types of de-essing without experiencing more blatant artifacts.

A more recent method of de-essing involves simply drawing automation curves whenever problematic sibilance occurs in a DAW. This method is not possible in the analog domain as it would require too great of a reaction time.

[edit] References

  • Jeffs, Holden, and Bohn, "Dynamics Processors - Chapter 4", in Dynamics Processors -- Technology & Applications, [1].
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