Quantization Grid, Split from Topic ID #55966 Options

[KMD]

I have thought that this phenomana may be real for years . I call it the "quantiztion grid". An analog waveform can change direction or cross the zero line at an infinite number of locations. Sampling and Quantization create a grid to which features of the waveform are statistically constrained. Increasing the sample rate at a fixed bandwidth inreases the quantization grid density. Whether it is perceivable is what is in question. This experiment may have proved it. I will give some thought to a simillar experiment that forum members can do for themselves and start a new topic on it.

[greynol]

Why do you keep insisting that dither must be present in order for there to be voltages between quantization steps in a reconstructed digital signal?

Tell me KMD, do you have any formal training or is this just from the seat of your pants?

This post has been edited by greynol: Mar 20 2012, 15:11

[2Bdecided]

Why do you keep insisting that dither must be present in order for there to be voltages between quantization steps in a reconstructed digital signal?

For a low-ish frequency input signal, ignoring noise etc, most of the instantaneous output voltages will be essentially "on" the quantization steps. You can see this very easily at low amplitudes.

Cheers,
David.

[Speedskater]

For a low-ish frequency input signal, ignoring noise etc, most of the instantaneous output voltages will be essentially "on" the quantization steps. You can see this very easily at low amplitudes.
Cheers,
David.

So you look at this instantaneous output voltage and if it is NOT "on" a quantization step - you say "ignore that, it's noise".
And if this instantaneous output voltage is "on" a quantization step - you say "see I told you so".

This post has been edited by Speedskater: Mar 21 2012, 00:34

[2Bdecided]

For a low-ish frequency input signal, ignoring noise etc, most of the instantaneous output voltages will be essentially "on" the quantization steps. You can see this very easily at low amplitudes.
Cheers,
David.

So you look at this instantaneous output voltage and if it is NOT "on" a quantization step - you say "ignore that, it's noise".
And if this instantaneous output voltage is "on" a quantization step - you say "see I told you so".

It's hardly cherry picking.

Here are two graphs showing the distribution of sample values.

This is from the 8-bit without dither data, 8x oversampled (i.e. resampled to 352.8kHz) at 16-bits...


This is from the 8-bit with dither data, 8x oversampled (i.e. resampled to 352.8kHz) at 16-bits...


In both cases, the dominance of the original 8-bit quantisation steps is clearly visible: those huge peaks match the original 8-bit quantisation steps. The skirts around them are due to the effect of the resampling. In a real system, noise would broaden the skirts and reduce the peaks - though not noticeably for 8-bits! More importantly, an AC-coupled system will see the values drifting around with any DC in the sampled waveform.

EDIT: These distribution graphs are for full 20s 20Hz-1kHz log sweep -40dB signals - the same ones from which the waveform images in this post were taken.

Cheers,
David.

This post has been edited by 2Bdecided: Mar 21 2012, 11:06