From Audacity Manual
Gale 05Dec13: ToDo-2 Possibly provisional new GUI committed as per image so text description needs review. I made a provisional revision of the text for inaccuracies I was aware of including clarifying for "Max" that this relates only to silences that were truncated.
- Gale 11Dec13:Made further tweaks including a potted explanation in intro. I'm not sure if this will actually help understanding.
- Steve 11Dec13: Is it worth mentioning that the deleted silence is from the middle of the detected silence? The term "truncation" may suggest to some that the deletion is from the end of the silence (not the case). The fact that deletion is from the middle has relevance if the audio fades in or out.
- Gale 11Dec13: Done.
- First, silences are detected that are at or below the specified threshold and are the specified "ignore" length or greater.
- Then compression (4:1 by default) is applied to that part of the detected silence that exceeds the ignore length, reducing the total length of the detected silence.
- Finally a "truncate to" length is specified which no truncated silence may exceed. If the silence remaining after compression is shorter than "truncate to", the actual length of the truncated silence will be that compressed length instead.
Throughout this description the words "silence" and "silent" mean sounds that are below the Threshold setting.
Threshold for silence
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. A ratio of 1:1 disables compression.
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
If the duration of a detected silence after compression is still greater than the "truncate to" length, it will be truncated to the "truncate to" length. The final duration of the detected silence will be this length unless it is already shorter. It may be convenient to think of "then truncate to" as the maximum length after compression/truncation.
- 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.
- 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. 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 length) = ((ignore silence length) + (waveform silence length - ignore silence 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 may remove the quietest part of fades. If you need to add fades, apply Truncate Silence before adding fades.|