Truncate Silence

From Audacity Manual

Use the Truncate Silence effect to automatically try to find and eliminate "silences" - that is, portions of the audio where the volume is below a set threshold.

Accessed by:

Throughout this description we will use the words "silence" and "silent" to mean sounds that are below the Threshold setting. We know that they aren't really "silent".

Min silence duration

This specifies the smallest resulting allowable silence. Truncate Silence will never shorten silent audio to less than than this amount, and silence durations shorter than this amount will not be altered. Default: 200 milliseconds.

Max silence duration

This specifies the longest resulting allowable silence. Default: 1000 milliseconds.

Silence compression

Silence compression is only used when Max is greater than Min. Periods of silence longer than the minimum silence duration will be compressed by this factor. Default: 4-to-1.

Threshold for silence

This threshold level is used to determine what is and what is not considered silence. Default: -40 dB.

Description

Truncate Silence removes, or reduces the length of, silent passages in your audio.

If you set both the Min and Max times to the same number, e.g. 200 milliseconds, Truncate Silence will reduce any period of silence less than -40 dB to 200 milliseconds.

Truncate Silence can also proportionally reduce silent periods. The author cites an example: "you can set the minimum to 100 milliseconds, the maximum to 5000 milliseconds, and the compression factor to 4:1, and it will have the result of about a 2x speedup in speech with no pitch change, and keeping about the same cadence as the original."

Proportional silence reductions operate according to the formula:

(output silence length) = ((min) + ((input silence length) - min))/compression) with the constraint that output must be less than the maximum length.

Also note that this formula cannot produce an output silence length that is shorter than the minimum length.

So if you set the minimum to 33 ms, a 1033ms silent period with 5:1 compression would be reduced to 233ms. (Unless of course, the maximum were set to less than that).

Note that if the selection starts out with silence, that silence will be truncated to the minimum value.

Limitations

Truncate Silence only removes audio, it does not reduce or eliminate noise in the silent sections that it keeps.

Avoid using Truncate Silence on audio after you use a fade-out or fade-in. Use Truncate Silence before these fade effects.