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How to calculate quantization noise from spectrum (Read 741 times)

Julian18

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Posts: 55

How to calculate quantization noise from spectrum
Dec 17^th, 2010, 5:09am

Hi all
it is just a trivial question.
How to compute quantization noise from its spectrum(from 0 to Nyquist frequency)?
suppose in matlab I have a variable QN, which is my quantization noise. of course I can do this:
Quote:

QNP1=sum(QN.^2)/N % where N is the number of point and assuming power of 2

suppose I also want to calculate that noise power from frequency domain. so
Quote:

s=abs(fft(QN));
s=(1:end/2)/N*2; % use only [0, Nyquist frequency] portion, and then scale the spectrum;
QNP2=sum(s.^2)

but this time I always get two-fold the number i get from time domain calculate(QNP1). I know I must have done sth. very silly, so please help me figure it out!

Thanks

Julian

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Julian18 Community Member Offline Posts: 55	Re: How to calculate quantization noise from spectrum Reply #1 - Dec 18^th, 2010, 2:24am bump
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boe Community Fellow Offline Posts: 615	Re: How to calculate quantization noise from spectrum Reply #2 - Mar 3^rd, 2011, 4:01am Julian18, You need to use the power over the full spectrum, i.e. Code: s=abs(fft(QN)) / N; % Scale %s=(1:end/2)/N*2; �% use only [0, Nyquist frequency] portion, and then scale the spectrum; QNP2=sum(s.^2) B O E
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ontheverge Junior Member Offline Posts: 31	Re: How to calculate quantization noise from spectrum Reply #3 - Mar 8^th, 2011, 4:38pm 1. make sure coherent sampling 2. q_noise_tot = sum(10^(x/10)) � �% add up over all non-DC, non harmonic bins. � u can convert tot q noise by 10*log(q_noise_tot)
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