Computer Audio Asylum: RE: Better duck under that desk; by Ryelands Music servers and other computer based digital audio technologies.

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Posted by Ryelands (A ) on August 10, 2009 at 06:26:29

In Reply to: RE: Better duck under that desk; posted by Werner on August 5, 2009 at 23:19:23:

werner argued that:

[the changes Kunchur has detected] can be resolved [by 44.1 KHz sampling].

The theoretical limit on the time resolution of a sampled quantised system is the sampling period divided by the number of quantisation steps . . .

Again, sorry for a late reply. I’m well out of my field here and haven’t found much by way of useful background. I’m not saying you’re wrong only that what you say seems directly to contradict what Kunchur says. See e.g. his “FAQ”:

Optical example: A binary star system is imaged through a telescope with a CCD. First, there is the analog optical resolution that is available, which depends on the objective diameter, the figure (optical correctness) of the optics, and seeing (atmospheric steadiness). This optical resolution is analogous to the "analog bandwidth". Because this resolution is limited, a point source becomes spread out into a fuzzy spot with an intensity profile governed by the point spread function or (PSF).

Next we are concerned with the density of pixels in the CCD. To avoid aliasing, the pixel spacing L must be finer than the optical resolution so that the optics provides "low pass filtering". If the pixels and their separation are larger than the separation of the centers of the two star images, the two stars will not be resolved separately and will appear as a single larger merged spot. In this case the essential feature (the fact that there are two separate stars and not an oblong nebula) has been destroyed. This is usually what is meant by "resolution" or the lack of it.

The number of bits N that can differentiate shades of intensity ("vertical resolution") has little to do with this – no number of vertical bits can undo the damage. However, details of the fuzzy merger do indeed depend on N: if the star images are moved closer together, the digital data of the sampled image will be different as long as the image shift exceeds L/N. This L/N definition of resolution applies to the coding itself and not to the system's ability to resolve essential features in the signal as described above . . .

and, in the next section (Digital Audio Recording):

However this lack of temporal resolution regarding the acoustic signal transmission should not be confused with the coding resolution of the digitizer, which is given by 23 microseconds/2^16 = 346 picoseconds. This latter quantity has no direct bearing on the system's ability to separate and keep distinct two nearby peaks and hence to preserve the details of musical sounds.

[Emphasis added - DB] You, OTOH, say that The (theoretical) temporal resolution of a 16-bit 44.1kHz sampled system is 22us/2^16 = 346 picoseconds .

I accept that Kunchur seems to confuse the notion of distinct temporal events with that of temporal resolution as investigated in his experiments and that that is unhelpful - but I don’t see it as critical to the argument.

What is more clear to me is that he says that the sampling rate is the sole critical parameter whereas you say that it is the sampling rate divided by the bit depth.

The two formulae cannot both be right - and the difference (here, nearly four orders of magnitude) is the nub of the argument as to whether RBCD is "perfect sound".

Comments?

Dave

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