Re: Noise Shaping and Clipping

Vladimir Vassilevsky wrote:

> 
> 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.
> 
> What do you think is right approach?

If the whole purpose of this system is digital processing of analog
signals,
(meaning analog in, analog out) then another solution would be to use
more bits in the processing chain and the DAC than the ADC provides, and
set the amplification factor of the output stage such that unity gain of
analog signals is garantueed.

bye
Andreas
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