Hello again Joe,
Dr. Pykett replied with the following, and kindly gave us permission to post it here, although he intentionally doesn't participate in forums personally (so as not to compromise his impartiality):
I can't see that the signal mixing issue has much to do with whether the samples are wet or dry. If they are wet, one nevertheless still has merely a single signal, statistically stationary in terms of amplitude and phase for each channel (L or R) for each sample emerging from the synth once the reverb has stabilised during the steady state phase of the sound, provided the note remains keyed for long enough. This signal has a defined harmonic structure in which each harmonic has a certain amplitude and a phase relative to some arbitrary datum. Other than minor random fluctuations, which also occur for a real organ pipe sample recorded in dry conditions, or synthesised artificially so as to include them, the amplitudes and phases of each harmonic remain pretty much stable for the purposes of this discussion.
If such a signal is then mixed (added) electronically with another of similar characteristics, then audible interference (in the technical sense of the word) will occur between every pair of harmonics with identical or near-identical frequencies in the two signals, as I demonstrated in my web article. When there is zero relative phase shift between each such pair, the resulting mixed signal for each harmonic pair will have an amplitude maximum, and when the phase shift is pi (180 degrees) it will be minimum. If in addition the amplitudes of each harmonic pair are the same, they will completely cancel in the latter case, as in the audio example on my website. Therefore, none of this has anything to with whether the samples are wet or dry.
For those who remain unconvinced, why don't they just try repeating the experiment described in detail on my site but using samples of any degree of wetness they choose? Or maybe you could do it for them and post the results for all to hear, as I did.
To repeat, note this has nothing to do with wet or dry samples once the signals have reached their steady state in the recording auditorium. There will of course be different, transient, effects during attack and decay due to the attack/release transients of the pipes themselves plus whatever impulse response characterises the particular environment they were recorded in, but a short time after key-down these effects will vanish. It is only during the steady state sound regime that phase interference effects are subjectively relevant for the organ.
Hope this helps.
With the greatest respect for him (and the many excellent and informative articles he provides), I think he has actually missed the key point (which could well have been my fault for not making it clearly enough in my original mail to him), viz.:
That two wet pipe samples when added together give an identical result to a recording of the two pipes sounding together provided that the wet samples were recorded according to the rules for wet sampling i.e.:
1. the microphone/ear didn't move throughout the entire recording process, and that:
2. they were synchronised properly, and that:
3. no other processing is performed on the samples which might affect amplitudes or phases.
However, Dr. Pykett doesn't wish to be involved in further discussion (or to respond to that specifically), so we must respect that and leave the question of how he sees that in relation to his 'signal mixing effect' not completely answered.
Moving on:
Speaking as somebody who has spent the majority of the last ten years of my life developing Hauptwerk based on the one key fact that wet sampling *does* work properly (i.e. that pipes can indeed be combined properly without the 'signal mixing effect' distorting the result when combined), believe me: it is a point I know very, very well indeed to be correct! Likewise it's the single fundamental fact upon which all wet sample sets, and all wet sample set producers (MDA, OrganART Media, Sonus Paradisi, ...) absolutely rely. If it didn't work properly, i.e. if the 'signal mixing effect' did mean that wet pipe pipes couldn't be combined digitally, then none of us would have been doing this, and the audio results you can hear wouldn't have been possible:
http://www.hauptwerk.com/learn-more/audio/To prove once and for all that wet sampling does indeed work properly, i.e. that it allows multiple separate pipe samples to be combined digitally to give the same result as a recording of the real pipes sounding simultaneously, I've spent today carrying out the experiment I described to you in my previous post. Everything is included in this ZIP, including the source sample files, and the resulting audio files:
http://downloads.hauptwerk.com/forum_temp_images/SignalMixingWithWetSamplingTechnique-AirVsDigital.zipOpen the .cwb file in Sonar to see the test. The first track is the signal that was fed to two loudspeakers (left to one, right to the other), placed at arbitrary points in a room.
The second track is what a microphone (placed at another arbitrary point in the room) picked up whilst the first first track was playing via the loudspeakers. (Only one (mono) microphone was used, so both channels of track 2 are identical.)
The input (track 1) contains, in order:
1. Test1Input-L.wav (a mono middle C diapson sample, fed to speaker 1)
2. Test1Input-R.wav (the same sample, repitched up 1 cent, fed to speaker 2)
3. Test1Input-LR.wav (both of the previous two samples, sounding together, each through their respective speakers, i.e. mixing 'in air')
4. Test2Input-L.wav (a mono middle C diapson sample, fed to speaker 1)
5. Test2Input-R.wav (the same sample, repitched up 5 cents, fed to speaker 2)
6. Test2Input-LR.wav (both of the previous two samples, sounding together, each through their respective speakers, i.e. mixing 'in air')
7. Test3Input-L.wav (a mono 500 Hz sine wave, fed to speaker 1)
8. Test3Input-R.wav (a mono 505 Hz sine wave, fed to speaker 2)
9. Test3Input-LR.wav (both of the previous two sine waves, sounding together, each through their respective speakers, i.e. mixing 'in air')
TestOutput-Complete.wav is what the mic picked up in its entirety whilst the above inputs were played in sequence. (It is the whole of track 2 from the Sonar project exported as a .wav file, and converted to mono, since there was only one microphone anyway.)
I used Sonar to play back the samples and to record the result in this way so that perfect synchronisation could be guaranteed throughout (using Sonar's timestamp), to avoid the need additionally to record MIDI synchronisation pulses.
I then cut up TestOutput-Complete.wav into nine parts, each starting at Sonar's timestamp for the start of the corresponding input signal (thus ensuring that synchronisation, and thus all relative phases, were preserved properly).
This gave the following files (in order corresponding to the input files above):
1. Test1Output-L.wav
2. Test1Output-R.wav
3. Test1Output-MixedInAir.wav
4. Test2Output-L.wav
5. Test2Output-R.wav
6. Test2Output-MixedInAir.wav
7. Test3Output-L.wav
8. Test3Output-R.wav
9. Test3Output-MixedInAir.wav
Using an audio editor, I then mixed the whole of:
- Test1Output-L.wav with Test1Output-R.wav to give: Test1Output-MixedDigitally.wav.
- Test2Output-L.wav with Test2Output-R.wav to give: Test2Output-MixedDigitally.wav.
- Test3Output-L.wav with Test3Output-R.wav to give: Test3Output-MixedDigitally.wav.
If wet sampling works properly, i.e. if it indeed is mathematically valid to sum two individual wet samples together with the 'signal mixing effect' producing a distorted result, then:
- Test1Output-MixedDigitally.wav should be identical to Test1Output-MixedInAir.wav and
- Test2Output-MixedDigitally.wav should be identical to Test2Output-MixedInAir.wav and
- Test3Output-MixedDigitally.wav should be identical to Test3Output-MixedInAir.wav.
Open them in an audio editor and compare them for yourself! They are indeed identical.
If you still doubt that it works, try the whole experiment yourself - you will get the same results.
I rest my case!
Having now spent almost three days of work in total replying to this topic and your previous (indirect) one on the subject of the relevance of 24-bit for sample sets, I'm going to leave this discussion here, I'm afraid (otherwise also Brett will be quite justified in killing me). Of course, feel free to continue the discussion, but I wanted to demonstrate once and for all why wet sampling is indeed valid (which I believe the above test results show absolutely conclusively), and I'll have to leave you to your own devices now.