More Clean-Up of Digitized Album #2
Last Updated: 03/20/2025
This page continues the discussion of Audacity's audio clean-up tools by documenting the usage of the Noise Reduction and Silence tools. Since the Repair tool was discussed on the Pre-Cleanup page, it is not covered again on this page.​​​​​
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Noise Reduction
Using the Noise Reduction tool is a multi-step process similar to Click Removal but with an extra step. In the first step, the tool needs a background noise sample, which is used to estimate what noise to remove from the recording in the second step. The steps to using the tool are as follows:
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Select a few seconds of a silent section of the recording. Some silence in between songs usually works well. The beginning or end of the recording can be used as long as the needle is on the album playing.
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Select the command that brings up the Noise Reduction dialog box (Figure 1). The noise reduction, sensitivity, and smoothing parameters can also be set in this step.
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Click the "Get Noise Results" button.
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Select the portion of the recording to which the noise reduction should be applied. The selection could be a specific noisy section of the recording or the whole recording.
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Select the Noise Reduction tool again. If the parameters were not set in Step 2, they should be set in this step. Then click the OK button.
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Since this tool can negatively impact the desired audio, it is best to replay it after noise reduction is applied to see if Noise Reduction garbled the desired audio. If it did, undo the Noise Reduction (EditâžžUndo menu or Ctrl-Z shortcut)
Note: To select the entire recording, type Ctrl-A or double-click on the recording.​​
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Figure 1. Menu Noise Reduction and its Dialog Box
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The Noise Reduction settings are not intuitive, so a short description is included below:
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Noise Reduction (dB): This determines the volume reduction to be applied to the identified noise. 6dB is the default setting, but typically, a 12-30dB setting is more beneficial. Several tutorials recommend 25dB, but this higher setting is probably more applicable to voice recordings.
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Sensitivity: Controls how much audio is treated as noise, ranging from 0 (off) to 24 (max). Higher sensitivity removes more noise but may also eliminate some desired audio. The Audacity manual suggests keeping it at the lowest value; I typically use the default setting of 6, with some tutorials recommending 12.5.
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Frequency Smoothing: This setting spreads noise reduction across frequency bands (1-12, 0=off), which can make artifacts sound more natural but may reduce clarity. According to the Audacity manual, lower settings are preferred for music.
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Figure 2 shows a couple of noise-reduction examples. The top two waveforms show a silent audio section, with the right showing a 12dB reduction. Note that some small clicks are still present. The lower example shows the selected silence used for the profile on the left and the result on the right.
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Generate Silence and Delete
Figure 2. Two Noise Reduction Examples
Since the Generate Silence and Delete functions have some similarities, both are discussed together. However, the results of using one versus the other are very different. The Generate Silence tool will completely remove all sound from a selected portion of an audio recording but does not remove any samples. This tool very simply sets all the selected samples to zero. This tool comes in handy for fixing the silence before a song or after a song.
Unlike the Generate Silence tool, the Delete tool removes the selected section samples, shortening the recording. Delete is also typically used before or after a song or at the beginning/end of a recording to remove a section of the recording.
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​Figure 3 shows two ways to invoke the Generate Silence command: under the File menu and under the Generate menu; both are highlighted with yellow. The Generate Silence shortcut key, Ctrl-L, can also be used. The Delete command is also under the File menu. The shortcut keys for the Delete tool are Ctrl-K or Delete keystroke.
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The steps to set up and run these two commands are pretty straightforward.
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In the waveform window, select the desired section of audio. This may require playing the recording and zooming in to determine the exact beginning and ending of the desired section of audio.
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Simply select the desired command, as shown in Figure 3. The yellow highlights show the two ways of generation silence, and the red highlight also indicates where to click the delete.
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Figure 4 shows an example of applying these commands to the end of a recording. On the left is the original recording, with blue highlighting the section of the recording to work on. The middle shows the result of applying Generate Silence, and the right example shows the result of the Delete tool.
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Figure 3. Menus for Two Silence Tools, and the Delete Command
Figure 4. Example at End of Recording showing Result of Silence (middle) and Delete (right)
After running through all the "Clean-up" tools to the point where one is happy with the results or, more likely, just tired of tweaking the recording, the next step is to export the audio. Before exporting, it can be helpful to label the recording so that important information, such as the album title and artist, is exported simultaneously.
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