Cleaning Kit

Cleaning Up Noisy Recordings

Trevor Wishart (July 2007)


The 'Cleaning Kit' was originally developed to clean up vocal recordings made in noisy environments.

Typical sources of noise might be ...

The Cleaning Kit uses some existing and some new CDP programs to tackle all of these situations. However, it is not possible to deal with all possible noise intrusions.
At present, the Cleaning Kit handles only mono files. To clean stereo or multichannel files you will need to split the source into its constituent channels and clean each channel separately.

The Cleaning Kit Framework

The Main Cleaning Kit window presents

The Cleaning Kit Tools and their Uses

There are currently 13 options for cleaning sources.
You can call any one of these options br pressing the button adjacent to its name.
When a tool is called, a new window will appear and you will be asked to enter relevant parameters for that Cleaning process.

The 13 Cleaning options are
  1. Clean General Noise

    This would typically be used to remove constant background sounds like air-conditioning or extractor-fan hum.

  2. Gate out Bad Signal

    This replaces unwanted sound by silence of the same duration. This can be used, for example

  3. Cut away Bad Signal

    This can be used, for example

  4. Reinsert Original Signal

  5. Remove Pitch in Signal

    This is a spectral subtraction process, and can be used, for example

  6. Remove Sound under Sibilant

    This is a filtering process, and can be used to remove intrusive sounds where the foreground speaker is using a sibilant
    Typical intrusions might be

  7. Remove Noise Above Signal

    This is a filtering process, and can be used to remove noise type intrusions
    Typical intrusions might be

    This often causes some degradation of the principal source at the point where the filtering is done.
    It is usually better to use spectral subtraction if this is possible at the particular time in the source.

  8. Low Frequency Problem

    This is a filtering process, and can be used to remove low frequency intrusions

    Typical intrusions might be
  9. Subtract Spectrum

    This is typically useful where a noise intrusion begins, ends, or overlays a time where the foreground source is silent, but then continues over the foreground source. You are asked to specify the place where the intrusion is not overlaying the principal source as well as the whole area to be cleaned. The process works by subtracting the former from the latter. It can sometimes be used instead of filtering or gating.

  10. Graft segment Elsewhere

    This is a last resort process, where nothing can be done to remove a noise intrusion. It allows you, for example, to cut a sliver of a sybillant from one part of the recording, and use that to replace a noise-intruded sibilant elsewhere.

  11. Insert Silence

    Cutting away bad signal can sometimes result in unnatural speech (or other) rhythms. These can sometimes be mitigated by inserting an appropriate durations of silence.

  12. Attenuate Level

    This can be used, for example, to compensate for the source's back and forth movement in front of the microphone.

  13. Dovetail the Ends

    This can be useful where a section of recording has been cut from a longer source. For example, a single voice is extracted from a conversation and the 2 speakers overlap at the boundary but, to preserve the sense of the speech, the overlapped segment has to be retained. Using other processes (pitch or sibilant removal, see above) may still leave some residual unwanted signal. This can sometimes be hidden by subtlely dovetailing the start (or end) of the recording.