From Audacity Manual
Truncate Silence automatically reduces the length of passages where the volume is below a set threshold level.
Throughout this description the words "silence" and "silent" mean sounds that are below the Threshold setting.
Threshold for silence
Audio at or below this amplitude will be regarded as "silence", so will be truncated.
Ignore silence less than
Specifies the shortest length of silence that will be truncated by the effect. Silent passages of this length or greater will be truncated. Silent passages of less than this length will be left unchanged.
Compress silence by
A compression factor which proportionally reduces silences in the waveform that are longer than the "Ignore silence less than" length. Compression is only applied to that part of the silence that is in excess of the ignored duration, so for the default compression factor of 4:1 that "excess" silence would be compressed to a quarter of its original length.
This setting has no effect if the "truncate to" length (below) is the same as or less than the "ignore" length.
and then truncate to
After any silence compression is applied as above, truncation is applied to the entire resulting silence. The "truncate to" length specifies the longest allowable resulting silence in those silences that are truncated.
- Setting the "truncate to" length to the same as the "Ignore" length will always reduce the truncated silences to this length.
- Silences longer than the "truncate to" length will remain if they were ignored by Truncate Silence because they were shorter than the "Ignore" length.
- If compression is applied, truncated silences may be shorter than the "truncate to" length.
- Simple usage: Setting both the "Ignore" and "truncate to" lengths to 5 milliseconds (ms) will truncate the silence to 5 ms. This is less than the length of a detectable silence, so will effectively eliminate it.
- Truncate length only: Set the "Compress silence by" factor to 1 (effectively disabling it). Now any silence longer than both the "Ignore" and "truncate to" length will be reduced to the "truncate to" length and never any less than that.
- Proportional length only: Set the "Truncate to" length to some large value, like 1000000. Now that part of any silence greater than the "Ignore" length will always be compressed by the "Compress silence by" factor.
- Proportional truncation with compression factor: The resulting silence is calculated according to the following formula:
- (output silence length) = ((ignore length) + ((input silence length) - ignore length))/compression)
- with the constraint that output length can't be more than the "truncate to" length.
So, setting the minimum to 33 ms and compression to 5:1, a silent passage 1033 ms long would be truncated to 233ms (33 + (1033-33/5)), unless "truncate to" was set to less than 233 ms (in which case truncation would be to that "truncate to" length).
As a real world example, setting the minimum to 100 ms, the maximum to 5000 ms and the compression factor to 4:1 will have the effect of doubling the speed of a speech track with no pitch change, while keeping about the same cadence as the original.
Truncate Silence only removes audio, it does not reduce or eliminate noise in the silent sections that it keeps.
|Avoid using Truncate Silence on selections which have fade outs or fade ins, since it will remove the quietest part of fades. If you need to add fades, apply Truncate Silence before adding fades.|