cerberus wrote on Sun, 13 February 2005 00:08 |
Could we be clearer about the difference between noise and distortion here ?
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If you add a signal to another signal and it is related, or correlated to the original signal it is distortion. This means that as the original signal changes in some way the added signal changes with it in some way. If the behavior of the new signal is completely unrelated to the original signal then it is noise. It is said to be "uncorrelated" error.
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I understand quantization error as "truncation distortion"; which can be mitigated by adding "dither noise".
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If there is no random behavior in the original waveform and we quantize it then the amplitude of the quantization error indeed is directly related to the amplitude of the signal. This is distortion. The error signal is correlated to the original signal.
If, however, there is noise added to the original waveform prior to quantizing (and at significant enough amplitude - let's say a couple of quantization steps in amplitude) then the quantization error after sampling will no longer be related to the signal itself and will instead be related to the random noise that we added first. Therefore, this quantization error is no longer correlated - it is no longer distortion. Instead it is completely random - determined by the (also) random noise that was added in the first place. This turns the quantization distortion into quantization noise.
Of course, if the signal itself has enough noise present from natural sources then it doesn't have to be added first. So if we just take a signal and record it in a noisy room with a noisy mic and a noisy pre, through some cables to a noise front-end of a converter then the natural noise is enough to decouple the quantization error from the signal itself.
Therefore my lesson all holds, but I simply did not want to venture into having to explain that the quantization error is only random if sufficient noise is present in the signal. This is why I asked him to just "accept" that the quantization error was random - if the recording is done properly it is. For the sake of the original poster, however, we just wanted to go one step at a time.
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If stochastics can be explained to a lay person, please try.
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That's it.
Stochastics is, in layman's terms, the study of random behavior. That's what we touched on above. We have to ensure random behavior is present (and at sufficient amplitude) before we can ensure that quantization error is random.
Nika