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CDs can, by a very narrow margin, reproduce sounds beyond which the human ear can detect. There’s a theorem that states you can perfectly reproduce a waveform by sampling if the bitrate is double the maximum frequency or something like that, and CDs use a bitrate such that it can produce just above the human hearing range. You can’t record an ultrasonic dog whistle on a CD, it won’t work.
It’s functionally impossible to improve on “red book” CD Digital Audio quality because it can perfectly replicate any waveform that has been band-passed filtered to 20,000 Hz or thereabouts. Maybe you can talk about dynamic range or multi-channel (CDs are exactly stereo. No mono, no 5.1 surround…Stereo.) It’s why there really hasn’t been a new disc format; no one needs one. It was as good as the human ear can do in the early 80’s and still is.
It is my admittedly limited understanding that we really can’t do better at digitally recording an audio signal than how red book audio does it, such that the microphones, amplifiers, ADCs etc on the recording end and the DAC, amp and speakers on the playback end are going to be much more significant factors in audio quality.