Nooby ADPCM Question by Kurausukun at 12:59 AM EST on February 2, 2015
This is just something I've been wondering about for a while, and I could never arrive at an answer. Although I know ADPCM can be anywhere between 2 and 5 bits, let's just assume it's 4-bit because that's what is most commonly used. Why does Foobar report a bitrate of 1536kbps (assuming 48000Hz)? Also, if I check the properties of the file, it says the 16 bits per sample... but that doesn't make any sense, right? ADPCM is lossy specifically because it's 4-bit, right? Or am I thinking of this all wrong? Bits per sample is the same thing as bit depth, right? So I would expect the bitrate to be 384kbps.
Foobar likely reports 16 bits per sample, 1536kbps, 48000Hz because those are the properties of the audio decoded into PCM codec (like what you'd find in a wav file), one of the most common uncompressed (and therefore lossless) audio codecs.
It's telling you about the decoded audio spit out by the vgmstream plugin, not the original audio files themselves.
ADPCM is lossy because it tries to predict the real value and codes the difference to it. The loss is because the difference has a resolution far more limited than the actual value, making it unable to code the exact value in many situations.
But what you are experiencing sounds like a bug.
by nothingtosay at 2:05 AM EST on February 5, 2015
I think that's just what vgmstream is written to report currently. I believe it used to say that XA was lossless, but now it reports it as being 4-bit and lossy, so somebody fixed that. Maybe someone will for ADPCM now too.