Spectral Expander

This tool can be used to restore the original volume dynamics of a dynamically compressed audio file, provided the following conditions are met:

• the compressor operated in a single band
• the noise floor is affected by the compression
• at least some band of the noise floor is relatively unobstructed by actual signal

Some possible use cases:

• tape recordings with aggressive automatic gain control (AGC)
• digital masterings with excessive single band compression such as the outtake fragments from the game The Beatles : Rock Band

How to use

1. Open an audio file.
2. Set frequency bounds of noise band to sample. The averaged volume for this band will be plotted for the selected channels.
3. Set dB clipping values for the noise band. You can also right click inside the chart to place the red dotted boundary lines. The part of the volume curve between both lines is assumed to be the noise floor and will be flattened. Use the upper limit to clip intruding signal transients to prevent silencing them.
4. Optionally adjust the smoothing value of the volume curve but the default seems to work very well.
5. Click Expand to write decompressed output file.