ADM converted audio is clipping

[doctorseus]

I tried to convert a ADM file (118 channels) with encoder_main and default settings and main branch to a iamf file. When looking and listening to the decoded file after using iamfdec the audio in most channels (I used speaker layout 5.1.2 /-s2) is distorted / clipping. Even after using -p and -l to apply attenuation for the decoder as I assumed it might be a problem introduced trough the decoder.

However, there is a tmp file called XXX_converted1.wav (16 channels) in my tmp folder which also already includes the clipped audio, so I assume the conversion tool is the culprit here.

I think the distortion is the result when there is a significant amount of channels with activity and they get down-mixed / summed up. LFE channel (LEF=4) is fine for example - but all other channels are distorted (L=1,R=2,C=3).

[jwcullen]

Thanks for the details.

Indeed XXX_converted1.wav is very early in the conversion process.

The default settings (subject to change) for that conversion are to convert it to third-order ambisonics. That 16-channel wav file you see is the intermediate conversion. Since that intermediate file is distorted, then the IAMF file, and decoded output will be distorted.

Your theory makes sense. "I think the distortion is the result when there is a significant amount of channels with activity and they get down-mixed / summed up."

Tagged as a bug. Seems like the folding process may need to be updated to be more careful to avoid clipping with many input channels.