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Comment by WorkerBee28474 | Hacker News Reader

IIRC CDs were the first use of dithering in audio. It's not distortion, but both it and distortion change the signal.

https://en.wikipedia.org/wiki/Dither

While its true that dithering changes the original signal, dithering is a necessarily evil that prevents quantization errors as a result of downsampling 24-bit+ source material due to CDs being 16-bit. It’s a choice between some barely audible noise, or some weird spectral artifacts..

I was under the impression that the dithering level is well below our threshold for hearing. Can someone confirm or deny that?

Dithering modulates the least significant bit of the audio signal, so at normal listening levels it should be inaudible. Of course, one can amplify the silence by 120dB or so and hear the noise.

Sources: http://www.dspguide.com/ch3/1.htm

https://www.bruce.audio/post/2022/05/26/dithering/

I often wondered about the noise I was hearing from my Discman with headphones. You'd hear this hiss when you pressed play, even before the CD loaded, so it was probably the cheap consumer audio hardware rather than the CD format itself.

I think an additional layer of hiss would show up when it actually started playing.

Indeed, no inexpensive portable digital electronics was going to give you perceptible-noise-free 16-bit audio.

Depending on how the original audio was mastered, it could also have it's own hiss in the sound data if the CD itself. You can tell if you load the raw CD data into a wave editor and see low amplitude noise where you'd expect silence.

This can be a contentious area as a lot of different sources will throw different figures for the noise floor of a CD. I recall anywhere from -98 to -130dB. Either value, at the minimum level, is something like 4.6dB. Which is completely inaudible in normal listening conditions.

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