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Re: Oh Really??

Hmmm....

I wouldn't think the digital filter should be doing anything different than an analog filter in its place (except is it more likely you can do it better and with perfect repeatability with a digital filter). It should not be averaging the signal, it should be applying as close to an ideal lowpass filter as it can to the signal. This is not averaging it is reconstruction which is why intersample peaking can occur. If I have a sine wave at exactly 1/4 the sample rate (1/2 the highest allowed frequency) in such a phase relative to 4 samples which represent a wavelength so that that all 4 samples are in the middle amplitudes of the wave (this is easier to sketch than describe) then reconstructed peaks are much larger than the sample peaks. Any good digital or analog reconstruction filter will produce the peaks correctly - averaging would fail this case miserably.

I am interested in this thought though that the correlated noise within the random noise is actually representative of the original sub-LSB signal. That would be a great result indeed.

And for John..

"However, if y'all look at the spectrum of the signal before the output filter, y'all see the tone, the images, and the noise. Y'all won't see any harmonics like y'all would see if the dither didn't work"

Maybe it would be more clearly stated "before any reconstruction filter" since a system with a digital filter generally has 2 reconstruction filters, the digital one which removes the images as you go to a new sample rate and the analog one which is removes that images from the signal at the new sample rate.

Also, but the question still remains what exactly is in the "noise" and is it truly random.

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