Hi, I just ran into this thread, apparently several months late. I have to agree about some of the problems that some have had with my DiffMaker program. In some setups, a good clean null is achieved when it should be (i.e., when two recordings recorded the same way are diffed). In others, the null will be poor, except at the midpoint of the overlapped area of the two recordings.
I recently ran into a good example of this myself. It seems the culprit is, as some here have suggested, varying clock speeds (I had thought it was Gain Drift, even modified the program to deal with that, but that wasn't it). Very small differences in the tracking of clock speeds between the source and the recorder will hurt the null. In some cases, the equipment used will track well, at least over enough time for the two recordings to be made. But too often they won't. For some tests (cables, capacitors, etc) this is easily dealt with, just use the same soundcard to emit the test sound track as is used to record with. That's the situation I mostly have worked with, which is why I didn't pick up on the importance of clock tracking (and also why I didn't highlight it in "big red letters" -- I'm just experimenting with this stuff myself, too, not dropping gold nuggets of wisdom here. And hey, I don't charge for this software!). I have made good diff nulls without clock tracking, but that appears to be a matter of luck. Much less than 1ppm tracking will be needed to get deep nulls, it turns out. I updated the help file and software notes to emphasize the issue of sample rate drift and matching. I have had extremely good results when I locked the soundcard (an ESI Juli@, used as an analog recorder)clock to a CD recorder's digital output. That is a good scenario, if it can be managed (it is easy with that sound card). I am working on a very-fine sample rate error detection and correction algorithm. It isn't difficult to do in general, the theory as most of you know is pretty straightforward, but getting it to operate within a reasonable amount of time is a problem. Maybe in DiffMaker v2 I'll have a way to do it faster. I have done some interesting tests comparing 24bit/192kHz recorded music with a 16bit/44.1kHz version recorded from the same mix. I sample rate converted with the "r8brain" software so both were at 192kHz, then diffed them. Even with the (I assume) imperfect sample rate conversion used, it was rather shocking how very low the "diff" recording was. I'd like to repeat with other recordings (192kHz WAV files, with 44.1kHz equivalents aren't easy to come by, does anyone have a source?), but for now I am less enthused by the idea of high rate sampling than I had been. -- bwaslo ------------------------------------------------------------------------ bwaslo's Profile: http://forums.slimdevices.com/member.php?userid=13548 View this thread: http://forums.slimdevices.com/showthread.php?t=37352 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
