16 to 24 bit MP3s

[Colin_Green1 (Colin Green)]

Can anyone shed light on the following. In my collection I have a number of MP3 files @ 320, 44.1/16. When played with Roon however, the signal path shows the source to be 44.1/24. No DSP is engaged so I wonder why this is so. Is bit depth somehow being increased from 16 to 24 and if it is, why?

[WiWavelength (Andrew J Shepherd)]

That the input to an MP3 encoder was 16 bit audio does not make the output a 16 bit MP3 file. Lossy codecs generally have no inherent bit depth and can be decoded to essentially any bit depth.

AJ

[BrianW (Brian)]

Also see this very useful post

ACC MP3 lossy output 24bit

Once audio has undergone lossy encoding, it no longer has an inherent bit depth. The encoded bits can be thought of as a mathematical description of how to reconstruct an approximation of the waveform that went into the encoder. The decoder usually calculates the reconstruction using floating point or integer math with at least 24 bits of precision. We chose to output 24-bit PCM in order to avoid introducing unnecessary dither to the decoded audio. Dither is basically a necessity when dropping a…

[Colin_Green1 (Colin Green)]

Many thanks, that’s useful to know.