after using Prosoniq MPEX2 for a test period, I feel obliged to report the results here.
In short, the results seem not very pleasant. For most of its normal settings, MPEX2 produces more or less audible, rather heavy distortions.
Within certain limits, it is possible, however, to work with MPEX2. But you won't find the tricks in the documentation.
Merging/Prosoniq are urgently requested to officially unveal the program's secrets, or better improve it so you can in fact use it as intended.
Let's have a look at the facts in detail:
1. Changing the pitch by fixed time scale (non-varispeed mode) results in distortions throughout.
If you try a signal close to a sine wave, you can hear additional, quite unpleasant tones (I don't know whether to call them "intermodulations", "residual tones" or whatsoever, sorry for my poor English. To describe the characteristics: when the original tone is "b", you can hear the lower notes "f" and "a flat", among other, higher tones. Let me call it "distortion" until someone tells me better.)
As a result, I would suspect that the pitch shift mode without varispeed is hardly of any use except for real emergency cases.
2. Pitch shift in varispeed mode
In most cases, you will hear the same distortions as described above, but with softer level, and starting after a certain time that varies between 2 and 10+ seconds. So the first few seconds (only!) are clean. The duration of the clean sound depends on the pitch value selected.
3. Now the good news:
with some particular pitch shift values, it works well for some longer time.
I made a test series for 48 kHz / 24 bit/ stereo, using a 500 Hz test tone with 40 sec. duration. There I found a kind of arithmetic order with no distortions occuring at all.
Those "good" fine pitch values ("fine pitch" represents 1/100 of 1 semitone, also called "cent") were as follows:
10 / 13,5 / 16,8 / 20 / 23,6 / 27,2 / 30,6 / 34,1 / 37,4 ...
Analyzing that order, I found their pitch relations very close to 48000/48096/48192/48288etc. or 1 : 1,002 : 1,004 etc.
The funny thing was, when I tried to verify those figures by a new test (after finding the formula), the distortions came in earlier again. Still better than normally, but not as ideal, and I don't have any idea which detail of my setup caused the difference. I simply gave up.
4. After all, it may be regarded another good news that in monaural mode all pitch values are o.k.! No distortion at all (please check for longer durations by your own, if you want to use this way...
). This fact proves that the program theoretically could work. Encouraging enough...
Regards,
Gerhard
Still we should consider the great contribution people like you give to our professional world.