For what it is worth, these are the versions I am using for test:
- LAME 3.100
- FLAC 1.3.4
- M4A - hard to say exactly, using the latest QAAC with CoreAudio from approx 1 year ago.
The others are sort of irrelevant, OPUS is not common for non web streaming, so that is out of scope.
EDIT: I wanted to add some other thoughts…
- The encoder settings are mastering steps. They have great impact on the result. The settings are never a “one size fits all”, if you want the best you can get.
- There is a (or can be a) tonal difference between the MP3 and M4A compression. I wonder if there is impact on AcoustID due to this. I am unsure.
- Using CoreAudio to create M4A files will produce a different result than using say libfdk_aac. They are different M4A files, no different than MP3 vs M4A.
- FLAC, while lossless, is not all the same. It depends on the source, and this applies to WAV as well. I can make a lossless at any point in the process, and lossless means only lossless to the source. Thus, the source is a critical component, which often causes a difference in a 16 and 24 bit FLAC.
- I have seen CDs that are not true 16 bit audio, so they actually differ from a true 16 bit FLAC.
- Editing iterations also have impact. If proper head room is not there, lossless starts to create loss in its result. This is a result of poor mastering, or a result of a limited source.
- The human ear, for most of us is only up to approx 16kHz, the logic of the MP3 cutoff. However, what is not considered is the result of not having the higher cutoff. Simply chopping the audio at a freq is nasty and can be heard, thus the head room need. I would expect this to also impact the AcoustID.