A WMA Professional stream of 16 bits per sample played about 48 dB
too quiet and with a noise floor near -70 dBFS.
ffmpeg scales the transform's output by the stream's sample size.
That was dropped when the decoder was converted to fixed point
(d884af2b99, 16284ae8ae), and the output is passed to the DSP as if
every stream had 24 bits. A stream of fewer bits has a lower
quantization step to match, so it came out low by the difference,
and it used the bottom of the integer quantization table, where the
factors have only a few significant bits.
Decode a 16 or 20 bit stream at the level of a 24 bit stream: use
that stream's quantization step, and scale each band's factor by
the ratio that is left. 24 bit streams are not affected.
Checked with perfsim (Sansa e200v1 build) against ffmpeg's decode
of a 16 bit, 192 kbps stereo file, the only such file to hand:
level SNR vs ffmpeg noise
before -48 dB 37 dB -70 dBFS
after correct 85 dB -117 dBFS
A 24 bit file's output is byte-identical before and after. The
20 bit case follows the same rule but is untested.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
6ffbee954b