Modern codec at a decent bitrate: inaudible.

Ironically, it could be the expensive DAC and headphones that helps the codec conceal itself.

That is to say, an audiophile who prefers gear that causes pleasant distortion might hear a difference through that gear, because the codec doesn't account for trying to mask its artifacts through equipment distortion (perhaps distortion in the ear itself only).

Say the codec removes something from the signal on the psycho-acoustic hypothesis that it is masked by something louder occurring close to before or after. That hypothesis is correct under hi-fi conditions, but suppose that the user's distorting tube power amp brings out that something, making it audible. Then removing it is potentially audible!