Alfred001 wrote:Would you say that it is still true that harmonic and intermodulation distortions are mostly dealt with at the source rather than through processing?
The problem is, as they say, "non-trivial." It is possible to measure and duplicate the transfer characteristic of an active device if one has access to it, but even so, it is not possible to determine exactly "where" on that curve a signal may have passed through it. Harmonic distortion will occur at predictable frequencies, but those are also the overtones of musical instruments. IM distortion generates sum and different frequencies, but the number of those increases geometrically with the number of frequencies present in the original signal. Not to mention that 3rd order products increase as the cube of the original signals' powers, fifth order to the fifth power, etc. For years there have been programs that calculate IM products for radio transmitting sites, but the calculations become unwieldy for a large number of transmitters. And these programs don't even attempt to consider non-periodic signals (irrelevant to the purpose.)
Not to mention that any commercial recording may have passed through dozens if not hundreds of active devices, at various unknown points on their individual transfer characteristics, which may (likely will) change dynamically even within a single track due to compression, gain riding, EQ changes, etc. So it would be impossible to accurately determine the individual contributions of all these things.
Which leaves us at basically trying to guess. Again, non-trivial...
I think for the archivist, the best one can do is to minimize the sources if distortion over which one has control, and perhaps make some adjustments by ear to what Copeland calls the "service copy." EQ and filtering choices would seem the most amenable to this subjective manual function.
Fortunately for me, I am not trying to make archival copies for the Smithsonian, but only my own personal enjoyment, so don't have to lose sleep over their lack of perfection...
Good luck with your paper!