I asked some questions about processing stereo cartridge playback of a monophonic LP in this thread
http://audiomastersforum.net/amforum/index.php/topic,6390.0.html
Discussion also got into certain aspects other than my specific questions. These other considerations may not have been entirely clear to me, but they did not lead me to believe my basic approach was deficient, even if not theoretically perfect. Since my final results have mainly been quite listenable, by the standards of my education anyway, I did not get any ideals, or feelings, that I needed to make processing changes.
Later I posted another thread about something I've noticed in a number of LP transfers.
http://audiomastersforum.net/amforum/index.php/topic,6317.0.html
The sample I posted happened to be a mono LP but I did not consider that significant. I did not think that my other observations of the characteristic in question were limited to mono recordings, although I find I'm not absolutely certain about that.
Anyway, MusicConductor returned my sample with his processing take. While my question was not exactly resolved in the abstract, his example gives a strong suggestion that what I hear and see is an artifact/distortion of some sort, not a natural characteristic of some instruments such as the trumpet in that sample. His processing removed what I though might be mis-tracking distortion, but his explanation says that it was something else, not distortion from mis-tracking as I thought it might be.
More troubling, or intriguing, is the sum of differences between my end result and his, much of which was totally unexpected by me. In a PM he told me the basic divergence was due to the second step listed in his 8/10/07 post, which he further described as "AA2's Center Channel Extractor with pretty aggressive settings". While he said he would eventually find time to provide more information, there is no reason to expect my inquiry to occupy his attention for long, and quite some while has now passed.
The difference is easy to hear and to observe in Spectral View, but that gives me no insight about why. I though that summing to mono was supposed to cancel everything that is out of phase. My best guess is that the process he used somehow went well beyond that which is out of phase according to strict numerical manipulation and applied some kind of logic that compensates for the fact that, due to cartridge, and other, manufacturing tolerances, playback isn't totally even from both channels.
In the first thread, younglove mentioned a "vinyl tuned" center channel extractor, but he did not say why it was desirable, at least in terms I understood. I guessed it was to be used
instead of summing the channels, but MusicConductor's approach seems to be from another direction, that of first removing something that summing can't handle.
Anyway, MusicConductor's result suggests that the processing I've been doing is some significant distance from producing a true representation of what was intended to come off the LP. younglove mentioned some more esoteric processes of matching frequencies and timing between channels to better preserve the high frequency information when summing to mono, while MusicConductor's approach seems to suggest that there is, possibly often, considerably more high frequency content in my transfers than the original recording ever captured.
Does anyone have any insight or comments about the differences between what I got and what MusicConductor got? My version of the program does not have the center channel extraction, and the vocal cut preset of the Channel Mixer does not produce anything approaching MusicConductor's results in any combination of processing steps I've come up with (I do understand that they are not comparable processes. It is just that sometimes, through multiple steps, the program may be able to accomplish things that have been made easier in later versions.). It may be that, if MusicConductors' result is the truer version, I'm just out of luck until I can upgrade the program, but suggestions for any other possibilities are welcome.