Thursday, July 20, 2017

Sigma Delta "Impulsivity"

One thing I've noticed recently in both 1-bit and multibit sigma delta DACs is something I call "impulsivity."  Peaks of loudness seem to get peakier, like tiny highlight spots of glare.

Now, firstly this could be just my imagination, I'm not going to even try to prove otherwise.

Secondly, sigma delta DACs, at least the better ones for quite some time have had better S/N and dynamic range specs than even the best, yes even my sacred 1704's.  So you could really say, black is blacker and therefore things rise up from the black with more contrast.  More contrast means more "peakier."

I'm suggesting something different.  I'm suggesting that when the sigma delta DAC has to output it peak it has to "work harder."  The way sigma delta dacs work is by a feedback loop, which drives the narrow converter to push the output into the correct signal.  When there is an actual peak in the signal, the overload is higher and the feedback has to work "harder," or at least more consistently, to one direction.  This is precisely the kind of thing our neural networks are designed to detect: correlation and causality and therefore intensity of effort.  We feel when things are struggling, or just loafing along.

The PCM dac, on the other hand, never "struggles."  It has the large jumps pre-fabricated and ready to go when needed.  It simply assembles the pieces for any given sample, and that is that.  It is therefore imperturbable (just loafing along).

Now I'm not suggesting some sort of ESP being involved, so how could we sense such things?  The answer is: it's below the noise floor, and the ultimate timing of things.

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