Vladimir Vassilevsky <antispam_bogus@[EMAIL PROTECTED]
> writes:
> Consider a requantization system with noise shaping and dithering.
> The question is what to do when the sum of the signal, the noise
> feedback and dither exceeds the range of the output quantizer.
> A differentiator of the Nth order used as a noise shaping filter has
> the max. feedback of ~2^N. So it is quite likely that the quantizer
> will run out of range at or near the peak values of the input signal.
>
> I can see the following approaches to this problem:
>
> 1) Limit the input signal so the requantizer will never run out of
> range. This works, however it reduces the available dynamic range. The
> reduction can be substantial if the noise shaping of high order is
> used.
>
> 2) Limit the sum of signal, dither and noise feedback to +/-max of the
> output quantizer. Calculate the feedback taking this limiting into the
> account. The result is horrid; error windup.
>
> 3) Limit the sum to +/- max. output, set the feedback to +/- 1 lsb
> accordingly.
Hey Vlad,
First of all, are you talking about an N-bit requantizer or a 1-bit
requantizer? I think you mean an N-bit, so that's what I'll assume in
the following.
I'm not sure what you mean by 2). Do you mean to simply feed back the
saturated N bits?
If not, then that would be the fourth, and most reasonable, option, in
my opinion.
In any case, the problem can be modeled as follows. The standard model
for a quantizer is a node that adds noise. If the input signal exceeds
the quantizer's range (and we saturate), then what changes is the nature
/ statistics of that noise. For one, the range of the noise becomes
greater.
So you may be able to resolve your question in these terms.
Note also that a 1-bit quantizer ALWAYS saturates!
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