I am not familiar with the term "introduced SNR"... Googling. No joy. I can't really follow your thinking above; sorry. In audio, there is distortion, which

I am not familiar with the term "introduced SNR"... Googling. No joy. I can't really follow your thinking above; sorry. In audio, there is distortion, which is correlated with the signal. Noise is uncorrelated. Codec error would seem very much to me to be at least much more correlated than uncorrelated. MP3 artifacts sound at least more "phase-ey" than they sound anything like quantitization noise ( at least to me ). This may be because I have heard badly aligned tape machines make that sort of error happen. "Phase-ey" also triggers my (feeble) mind into thinking about allpass filters as the model for the error. In terms of intelligibility, it's possible to improve intelligibility by adding noise, and by adding clipping - aviation comms does this at times. What destroys intelligibility is phenomes being destroyed by phase changes and bad amplitide errors ( where there are actually good amplitude errors ). I've run an ABACUS voice quality analyzer several times, and I don't think it's purely a distortion analyzer - adding clipping at least can improve MOS/PESQ score surprisingly. Even more surprisingly, there's no mechanism available for calibrating gain staging on one.