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Re: Pitching and Equalization of 78s

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Wed, 27 Aug 2003 19:42:52 -0600

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 ```Aaron wrote: > I am surprised that "pitching" is being suggested ex post facto as the > proper procedure for doing a 78 transfer. The reasons are as follows: > > 3. The final reason is that the algorithms which are used to achieve > this pitch change simply > go back and toss out enough samples to make the program the desired > speed or length. This I believe is not correct. Implicit in the assumption of samples is that they represent points along a wave form which is the Fourier sum of sine waves. Thus by doing the D-A conversion (but not really), one can predict with high precision the value a sample should have that's arbitrarily somewhere inbetween any two samples (which is what resampling is intended to do, at least that's how I understand it.) Thus, I am of the understanding, which may be wholly wrong, that the published algorithms for digital resampling are very well developed and universally implemented by the better sound processing tools. And that one can even predict the distortion caused by these algorithms, and that it is typically very small. But then, I've been surprised by what these tools can and cannot do. Anyone? (Btw, I just found the following online document goes into the general resampling algorithm known as "Bandlimited Interpolation": http://ccrma-www.stanford.edu/~jos/resample/resample.pdf It states on page 2: "...Since Shannon's sampling theorem says it is possible to restore an audio signal *exactly* from its samples, it makes sense that the best digital audio interpolators would be based on that theory. Such 'ideal' interpolation is called *bandlimited interpolation*." Putting it another way, if we accept that, in principle, we can do a D-A conversion, and then resample that using A-D, then we don't run into the problems Aaron is mentioning. Thus, this resampling can be done without ever going into the analog realm. Even if some audio processing tools don't use bandlimited interpolation -- and maybe Aaron is referring to some of these "cheap ones" -- one can certainly find a specific tool, and probably free, which does proper resampling.) There's a lot of factors to take into account when transfering, and adding precise pitch control in the analog stage is just another added burden if it is not necessary and there are other reasons not to do it (like one has to do a large number of transfers in a limited time frame -- digital restoration is done at a later time and at a more "leisurely" pace.) Of course, if one has the time to do it in the analog stage, then there's nothing wrong with that (although one may be able to do spectral analysis or some such tool in the digital realm to very precisely fine-tune the pitch.) > 4. For these reasons I believe that (with the exception of the Weiss > EQ-1) a really fine analog(Sontec) > EQ with an excellent turntable turning at the exact required playback > speed will in general reveal far more musical results > than attempting either eq or pitch changing in the digital domain. I > think it is unlikely to change in the near future. George Morrow did mention the need to try to get the equalization right in the analog realm before digitizing. He said the equalization can be done using a simple change in capacitance (or whatever) in the phono input, to emulate what was done years ago. He also said that someone has actually put together the table of values to use depending on label and label number -- by and large, he said, the recording companies kept their equalization settings the same for a period of time (but not always), since that was tied in with the "marketing" of their product, and they wanted uniformity in the equalization. Again, comments from the experts on both of the above are wanted. Jon ```