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NOTE: I got a little burnt out by this point taking notes during the class, and haven’t made the time to come back and flesh these notes out. Will do this asap. — Neth.

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• Table of Contents (if the right-side menu isn’t showing)

Week 6 - Compression

Compression

Allows us to control the dynamics of an audio signal.

• Think of it as a ‘volume leveller’.
• It brings out the detail of the audio signal, and makes it so the loud peaks don’t “stick out.”

Dynamic Range

Dynamic Range describes the difference between the loudest and softest part of an audio source.

• The higher the dynamic range, the larger the gap between the loudest and softest parts of the audio source
• The lower the dynamic range, the less of a gap between the loudest and softest part of an audio source

In the process, a source’s volume level, frequency content, dynamics, and panoramic position are manipulated or enhanced.

Image recreation based on image included in research paper: Hyper-compression in Music Production: The Loudness Normalisation Revolution and Implications for Music Streaming Delivery Platforms, Robert W Taylor at University of Newcastle Australia, August 2016.

Transients - Recap

A transient is a short-duration signal that represents a nonharmonic attack phase of a sound source.

Think of the initial sound you may hear when you hit a snare drum; the initial thwack – and the resulting peak you will see in the waveform – is a transient.

A more VO-related example would be words spoken with a hard staccato that often results in “plosives” – eg. a hard p or t can form a spoke at the start of the waveform of the word itself.

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Compressor Controls

Threshold

“Captures the emotion of the delivery.” The threshold is a control that tells the compressor when to start compressing the signal. Once the audio signal crosses over the threshold, the compressor kicks in and starts to compress the audio signal to deal with the louder peaks — essentially adjusting the gain — and then later you can work with “makeup gain”.

The threshold doesn’t become a hard limit, but rather things above it are attenuated on the scale. The only time it becomes a hard limit is when you have a “brick wall limiter”, designed specifically to halt all signals at that point.

Ratio

Ratio is a control that tells the compressor how much to compress the audio signal.

As soon as the signal gets louder than the threshold, the compressor will start working.

• For example a 2:1 ratio = For every 2 dB over the threshold, only 1 dB will be output.

If we refer to the image to the right, for every first number that exceeds the threshold, it will return the second number (which is typically one).

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For VO, Tony recommends between 2:1 and 4:1, otherwise you’ll start to really notice the compression on the voice.

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Attack

The Attack controls how fast the compressor starts working after the audio signal crosses the threshold.

• If your attack is too fast, you can start to lose your transients — the initial spike / sound at the sound of words, especially with letters like T or P etc. — which will sound very strange.
• If your attack is too slow, you won’t be achieving the right sense of speed in “smacking” the signal.

Release

The Release controls how fast the compressor stops compressing the signal after it falls below the threshold.

• This is essentially how quickly we want the compressor to “let go” and allow the signal to go back to its regular levels.