I think they mentioned ReplayGain with AAC and ogg formats, but it's possible they use some custom implementation. There's a good deal of information[1]; it is indeed not peak normalization:
> ReplayGain is different from peak normalization. Peak normalization merely ensures that the peak amplitude reaches a certain level. This does not ensure equal loudness. The ReplayGain technique measures the effective power of the waveform (i.e. the RMS power after applying an "equal loudness contour"), and then adjusts the amplitude of the waveform accordingly. The result is that Replay Gained waveforms are usually more uniformly amplified than peak-normalized waveforms.
Generally we indeed target both up or down in loudness (although 'up' is quite rare, typically high-end recordings of classical or jazz or otherwise very dynamic pieces).
Honestly, everything I read screams that Spotify really hired the right people to make these decisions.
Now I only have to rent about their handling (or rather, lackthereof) of metadata — how hard is it to display an actual first release date? but meh. Audio quality is great, no question about it. I just wish they'd stream FLAC in very-high quality + "quiet" environment settings (the "pure hi-fi" experience so to speak), but that'll come in due time I suppose.
> ReplayGain is different from peak normalization. Peak normalization merely ensures that the peak amplitude reaches a certain level. This does not ensure equal loudness. The ReplayGain technique measures the effective power of the waveform (i.e. the RMS power after applying an "equal loudness contour"), and then adjusts the amplitude of the waveform accordingly. The result is that Replay Gained waveforms are usually more uniformly amplified than peak-normalized waveforms.
Generally we indeed target both up or down in loudness (although 'up' is quite rare, typically high-end recordings of classical or jazz or otherwise very dynamic pieces).
Honestly, everything I read screams that Spotify really hired the right people to make these decisions.
Now I only have to rent about their handling (or rather, lackthereof) of metadata — how hard is it to display an actual first release date? but meh. Audio quality is great, no question about it. I just wish they'd stream FLAC in very-high quality + "quiet" environment settings (the "pure hi-fi" experience so to speak), but that'll come in due time I suppose.
[1]: https://wiki.hydrogenaud.io/index.php?title=ReplayGain