Truncate Silence - Audacity Manual

# Truncate Silence

### From Audacity Manual

Truncate Silence automatically reduces the length of passages where the volume is below a specified level.

- Silences are detected if they remain below the specified level for at least the specified duration of time.
- Detected silences (defined as above) are then made shorter by deleting a section from the middle of the silent region.

For the purposes of this effect, the words "silence" and "silent" mean sounds that are below the detection level.

  Accessed by: Effect > Truncate Silence...

## Operation Mode

There are two methods available for shortening the silence. The simplest method is by truncating the silence (default mode) and a more advanced method is by compressing the length of the silence.

### Truncate Detected Silence

When this method is selected, silences are simply shortened to the "Detect Silence" duration (see example below).

When this method is selected, the "Truncate to:" (seconds) control is available lower down the interface and the "Compress to:" (percent) control is grayed out. All detected silences are shortened to the same duration.

### Compress Excess Silence

This is a more advanced mode that allows silences to be shortened proportionally according to their original duration.

When this method is selected, silence in excess of the "Detect Silence" duration is reduced to a percentage of its original duration (see example below).

When this method is selected, the "Compress to:" (percent) control is available lower down the interface and the "Truncate to:" (seconds) control is grayed out. Because silences are reduced by a specified percentage, the final duration of each detected silence varies according to its original length.

## Detect Silence

There are two controls that determine which audio will be treated as "silence":

1. Level (dB): To be treated as silence, the audio must be below this level. If not enough silences are being reduced, increase the level to a higher (less negative) number. Note that due to rounding, audio may be truncated that appears in the Amplify effect to be exactly at the level you enter here.
2. Duration (seconds): The minimum duration that will be treated as silence. To be treated as silence, the audio must remain below the "Level (dB)" entered for at least this amount of time. If not enough silences are being reduced, reduce this duration level. The shortest duration value you can enter is 0.001 seconds.

## Reducing the length of detected silences

There are two controls that determine how much silence is removed, and hence the final length of each silence. Only one of these controls is available at a time.

- Truncate to (seconds): Only available when the simple Truncate Detected Silence method is selected. When the audio remains below the "Detect Silence" level for at least the "Detect Silence" duration, it will be reduced to the "Truncate to" duration entered here.
- Compress to (percent): Only available when the advanced Compress Excess Silence mode is selected. When the audio remains below the "Detect Silence" level for at least the "Detect Silence" duration, any silence in excess of the "Detect Silence" duration is reduced to the "Compress to" percentage entered here. The entire detected silence is not proportionally reduced.

## Examples

### Truncate Detected Silence examples:

#### Shorten all silences that are longer than 2 seconds to 2 seconds

This may be useful for shortening inter-track gaps from an LP or cassette recording.

1. Set the Operation mode in the dropdown to "Truncate Detected Silence".
2. Set the detection "Level:" control. If there is noticeable background noise you may need to set this as a higher (less negative) value than the default.
3. Set the detection "Duration:" control to 2 seconds. Silences of 2 seconds or more will be chosen by the effect for truncation.
4. Set the "Truncate to:" control to 2 seconds. All detected silences will be truncated to 2 seconds.
5. Click OK.

#### Shorten silences that are 20 seconds or longer to 5 seconds

This may be useful for removing long pauses in a speech recording, without affecting the natural rhythm of the speech.

1. Set the Operation mode in the dropdown to "Truncate Detected Silence".
2. Set the detection "Level:" control.
3. Set the detection "Duration:" control to 20 seconds. Silences of 20 seconds or more will be chosen by the effect for truncation.
4. Set the "Truncate to:" control to 5 seconds. Silences of 20 seconds or more will be truncated to 5 seconds. Silences of less than 20 seconds will remain unchanged.
5. Click OK.

### Compress Excess Silence examples:

#### Compress silences that are longer than 2 seconds

This may be useful when a subtle reduction of longer silences is required while maintaining a sense of the relative length of each silence. In this example we will use a compression setting of 50% for simplicity.

1. Set the Operation mode in the dropdown to "Compress Excess Silence".
2. Set the detection "Level:" control.
3. Set the detection "Duration:" control to 2 seconds.
4. Set the "Compress to:" control to 50 percent.
5. Click OK.

- Silences that were originally less than 2 seconds duration will be unaffected.
- Silences that were originally exactly 2 seconds duration will be detected, but the excess silence is zero so no shortening will occur.
- All silences that were longer than 2 seconds are shortened.
- The new length of the silence will be comprised of 2 seconds (the ignored duration) plus half (50%) of any additional silence.

Example: With the above settings, for an 8 second silence, there are 6 seconds beyond the 2 second detection period: The 8 second silence will therefore be reduced to 2 seconds plus 50% of 6 seconds, that is 2 + 3 = 5 seconds.

#### Compress all silences to half their original duration

Strictly speaking all silences cannot be selected because there is a fixed minimum length of silence that can be detected of 0.001 seconds. However, 0.001 seconds (1 millisecond) is an extremely short period, so we are able to compress all noticeable silences to half their original length. This may be useful to shorten a recorded lecture or dictated notes without affecting the words.

1. Set the Operation mode in the dropdown to "Compress Excess Silence".
2. Set the detection "Level:" control.
3. Set the detection "Duration:" control to 0.001 seconds. Note that if set to 0 the Preview and OK buttons are grayed out and a message is shown above the buttons: Minimum detection duration: 0.001 seconds..
4. Set the "Compress to:" control to 50 percent.
5. Click OK.

## 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 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.

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