[tacos]

I wrote some of those original codecs. I'm aware of what they do. :) The original SoundBlaster card was 8-bit. Creative ADPCM is 8 bit. Dialogic ADPCM -- basically every recorded sound you've ever heard over a telephone -- is 12 bit. You are correct with the modern definition but I'm talking about 20 years ago so let's not stomp on history for sake of Hacker News karma points.

The Microsoft article gets a few things wrong. The distorted sound is not due to reducing the sample rate. The distorted sound comes from taking a perfectly-good 11k file and then ADPCM compressing it. This is obviously due to throwing away information on each sample as part of the encoding process, not anything due to sample rate. (Of course it sounds better at higher sample rates. More data, more better.)

ADPCM for telephony seldom even hit 11k rates. 6000 and 8000Hz ADPCM files are common. (And nope, not 16 bit either.)

[acqq]

I fully agree with you re 8-bit SoundBlasters and phones. I was talking about the music recorded for CDs, 16-bits. Converting that to ADPCM was certainly not a process that was guaranteed to automatically give the good results but it was at least possible to produce reasonably good sound and save some space.

I'd be of course happy to hear something more about the work you did.