Conversion from 8-bit .au file to wavpack produces distortion

[bravemenrun]

Describe the bug
If you convert an old 8-bit .au file to wavpack the resulting file will have distorted peaks.

To Reproduce
Steps to reproduce the behavior:

1. Add an 8-bit .au file to the joblist
2. Select wavpack as the output format
3. Start encoding
4. The encoded wavpack file will have heavy audible distortion

Expected behavior
I would expect it to create an identical copy in a different format.

Screenshots

File 1 (Original)

File 1 (Wavpack)

File 2 (Original)

File 2 (Wavpack)

System (please complete the following information)

• OS: CachyOS Linux
• CPU: AMD Ryzen 7 5800X
• RAM: 64GB

Additional context
I must confess, I don't have many 8-bit .au files to test so I can't confirm every .au file is affected. Also, just out of curiosity, I tried converting the .au files to .wav files. The .wav files were an exact copy. I then tried to convert those .wav file to wavpack and the same distortion presented itself. I realize this issue is likely to affect close to no one but I figured it might be worth reporting anyway.

[enzo1982]

Thank you for reporting this!

I can confirm that distortion at the end of the file is introduced when trying to convert signed 8 bit audio to some formats, including WavPack and Musepack.

This appears to be a bug in how the sample format converter is used by the adapter for external codecs.

Some of fre:ac's specs for external codecs explicitly specify unsigned 8 bit input (e.g. OptimFROG or TAK). These do not show any distortion. Others do not specify this in which case the conversion to 8 bit unsigned is done implicitly due to WAV (which only supports unsigned 8 bit) being used as the transfer format.

When adding the Sample Format Converter filter and setting 8 bit unsigned as the target format, the distortion also goes away with WavPack and Musepack.

I'll try to find a fix as soon as possible.