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RE: Here's A More Direct Source

"And, yes, that's ANALOG FM, as started back in the 1960's! Digital FM is of course even more convoluted. "

Zzactly. I have been in arguments about whether that is actually quantizing or not. It is in one dimension but not the other. It is quantized in time but not amplitude, there are still an infinite number of amplitudes. But there is still that time thing.

Now when we quantize the amplitude a few other things happen. First of all if the source is completely noise free they have to add noise to it, it is called dither. It is just enough to trigger the ADCs and it sort of biases them like an amplifier. In fact on the old AAD CDs made from the old master tapes they had enough noise on them from the tape to not need dither and in some cases the quantization process subdued the noise in a very unobtrusive way, no Dolby, DNR or DBX or anything of the sort.

I actually was thinking of building a device that would do that outboard, and user calibratable. Set up a nice high bitrate, but then the lower bits close to digital zero are expanded just a bit to ignore most (but not all) of the hiss from the tape or whatever. Turned out that really the demand would never be enough and I would need too much help on it to really make money. To do it right you have to modify an ADC and really, the AAD CD did it well enough anyway.

But when they got to the DDD CD they had to add he noise, which you never hear. People, I mean alot of people REALLY could hear the difference, not just the golden ears. The dither, which is basically white noise actually biases the system just like an audio amplifier. you don't hear it, but without it, it just sucks. In fact even though they are extremely rare, there have been designs of amps with AC bias or even noise bias. Long abandoned designs, and I am not sure why. It almost seems more logical because it would tend to linearize the outputs' gain at lower levels better than DC bias. Or maybe not. Whatever. Since we do not hear of this now it obviously failed. Maybe it was too hard to get the thermal tracking right, I dunno.

But the fact remains that regular people could hear the difference, not just audiophiles, so they put the dither in.


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  • RE: Here's A More Direct Source - JURB 04:26:34 12/11/16 (0)

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