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Re: A lot of people don't understand dither

*** How about the thermal noise generated in all (equivalent) circuit resistances ***

I've already covered this in my other post.

"A good mic, mic pre amp and analog console have dynamic range of around 130dB. A good ADC will have dynamic range slightly exceeding 20 bits.
So, the noise floor of electronics alone are too low to produce self dithering when truncating from 24 to 20."

*** Have a look at the self-noise of your own minimalist recording setup. ***

Yes I have. I have two mixers, 4 sets of 24-bit ADCs, a few amps, mics, lots of keyboards (I did my thesis in computer music) so it's hardly "minimalist". I have also used a few studios.

*** Your analogy is wrong because in the case of truncating an image from 8/8/8 to 5/6/5 the target quantisation noise floor is so high that there is no dither-able noise present in the image at that level. ***

The analogy is apt because I am asserting (based on my experience) that there is usually no "dither-able noise" present above 20 bits in audio, therefore there is a benefit to dithering if truncating to 20 bits.

*** Most of the noise visibly present in the source image is correlated and/or of insufficient bandwidth (shot-noise, algorithm quantisation and errors, dark current, and the shot-noise of the dark current ... none of them remotely gaussian). That's why you need to add external dither. ***

Your argument applies equally to audio. That's why it's a good analogy. As I've mentioned in my other post, you can do the measurements and check it out yourself. The "thermal noise" that you speak of is typically not at -120dB, it's much lower than that (at least on my equipment anyway). What's at -120dB are harmonic spikes which is insufficient to cause dithering, and will *benefit* from being smoothed out through dithering. :-)

Put it this way, if the statement was whether there is any benefit in dithering when truncating to 22 bits (instead of 20) - I would say "probably not". But those 2 bits make a big difference, because that's where the "wideband" noise you speak of resides.


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