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Samples slightly distorted

Sampling pipe organs and turning them into something you can play in Hauptwerk.

Samples slightly distorted

Postby tf11972 » Mon Jan 23, 2017 3:42 pm

For our new sampleset I have recorded an overblowing flute. When I play the stereosamples (all containing 6 overlapping loops) in an audioeditor, they all sound perfectly, the loudest tone has an amplitude of -6.5 dB.
When I load them in Hauptwerk via a CODM, they all sound slightly distorted, especially when I play chords.

For information, we have set the amplitude of the rank in the CODM to 10 dB, the rank stands in a swellbox, windmodel is activated (deactivating shows no effect). Reducing the amplitude to 5 dB, the distortion doesn't disappear. Polyphony is set to 1984.

What could be the cause for this issue? Thanks in advance for your help.
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Thomas

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Re: Samples slightly distorted

Postby tf11972 » Tue Jan 24, 2017 6:04 am

Maybe this is the cause:

http://www.sonusparadisi.cz/en/blog/aliasing-due-to-repitching/

Due to several recording sessions at different temperature, we had to repitch the flute at about 28 Cent. I try this out to set back the samples to their original pitch.

Does anyone know a workaround to prevent this? Is it better to repitch the samples in an audio editor in advance?
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Re: Samples slightly distorted

Postby mdyde » Tue Jan 24, 2017 7:20 am

Hello Thomas,

Aliasing (as referred to in Jiri's article) is only likely to be audible if you're using Hauptwerk to re-pitch a sample (in real-time) by a significant amount, e.g. if you're asking Hauptwerk to re-pitch a sample to a different note or notes. If that's the case then yes -- it's definitely much better to re-pitch the WAV file yourself first using a high-quality (=>slow) re-pitching algorithm in an audio editor.

You could check whether that is indeed the issue by temporarily disabling real-time interpolation on Hauptwerk's 'Organ settings | Organ preferences | Audio engine' screen tab.
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Martin.

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Re: Samples slightly distorted

Postby Morse » Tue Jan 24, 2017 10:06 am

Hello Martin,

When you refer to Hauptwerk repitching a sample "in real-time" does this include the creation of missing notes during cache creation? Is the repitching algorithm during cache creation better than that used during vibrato, wind modulation etc? What I'm really wondering about is possible distortion created due to the very questionable practice of only sampling an organ every three or four notes.
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Re: Samples slightly distorted

Postby mdyde » Tue Jan 24, 2017 10:17 am

Hello Al,

All of Hauptwerk's re-pitching is (currently) done in real-time, so asking Hauptwerk to re-pitch one sample to different/several notes might give a certain amount of noticeable distortion. If it's necessary to re-pitch a sample to other notes then it's much better (in terms of quality) to use an audio editor to do it using a very high-quality re-pitching algorithm, as part of the sample set production process.
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Re: Samples slightly distorted

Postby tf11972 » Tue Jan 24, 2017 10:21 am

Thank you for your reply, Martin.

Unfortenately it is not possible to untick real-time-pitching in the organ preferences (the field is grey), but I'll give it a try and repitch the relevant samples in an audio editor first.
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Re: Samples slightly distorted

Postby mdyde » Wed Jan 25, 2017 6:30 am

Thanks, Thomas.

For testing, to enable that menu option you could edit the 'full-format' ODF to set _General.AudioEngine_EnablePlayingWithoutInterpolation=Y. (The CODM always compiles that option to 'N'.)
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Re: Samples slightly distorted

Postby tf11972 » Wed Jan 25, 2017 1:26 pm

Thanks, Martin.
Repitching didn't help. Maybe it's something wrong with my samples.
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Re: Samples slightly distorted

Postby mdyde » Thu Jan 26, 2017 5:47 am

Thanks, Thomas.

Does Hauptwerk's audio level meter on the 'Audio, MIDI and Performance' large control panel go into the red or yellow?

If not, does setting <compiled full ODF>._General.AudioEngine_EnablePlayingWithoutInterpolation=Y and then re-loading the organ (directly, not via 'Design tools | Load custom organ', since that would overwrite the edited compiled ODF), then also setting *all* of the following on the 'Organ settings | Organ preferences | Audio engine' screen:

- Disable interpolation = Y
- Disable harmonic-shaping filters = Y
- Disable swell box filters = Y
- Disable per-pipe EQ = Y
- Air flow randomisation adjustment = 0
- Disable wind supply model = Y (on the Wind Supply Model tab)

... eliminate the distortion? (If it does then it suggests that you might have some rank settings set so that the filters, pitch, or wind model are doing something extreme/unintended.)
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Re: Samples slightly distorted

Postby tf11972 » Thu Jan 26, 2017 6:46 am

I'm always thankful for your quick and helpful answers, Martin :D

I can answer your question with "completely no". Only one light in the audio level meter shines during playing the flute.

I'll try out your suggests und look if these improve my situation.
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Re: Samples slightly distorted

Postby tf11972 » Wed Mar 08, 2017 11:49 am

After many trials and errors I have finally solved the problem:

In the last days I had edited some of the samples to delete some remaining distortion frequencies with a highpass-filter. After that they sounded absolutely clean on my PC, but after loading in HW the distortion got worse.

And then I discovered the WindSupply_MaxFlowRandomisationPct entry in the CODM which we had set to 5. While all the other ranks are profiting from this parameter, the overblowing flutes show an allergical reaction. Now I have disabled this for these ranks and the distortion is gone :D
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Re: Samples slightly distorted

Postby mdyde » Wed Mar 08, 2017 12:17 pm

Hello Thomas,

Thanks for the update, and glad to hear you've managed to resolve it now.

If the issue was related to flow, then my guess is that the harmonic shaping filters were emphasizing the rank's distortion frequencies. Assuming so, you could instead potentially try reducing its HarmonicShaping_PipeMIDINoteNum..._WindModelModDepthAdjDb values (i.e. making them more negative).
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Re: Samples slightly distorted

Postby tf11972 » Wed Mar 08, 2017 12:23 pm

Thanks Martin, for your quick reply. I will try this out.
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Re: Samples slightly distorted

Postby tf11972 » Thu Mar 09, 2017 8:47 am

Hello Martin,
to reduce the amount of the harmonic shaping filters didn't show the wishing effect (the flutes lost their character and the distortion remained).

Edit: I apologize for my acclamation of success, I must have sitten on my ears yesterday :( Today the distorted samples were really the same, also when I disabled the wind fluctuation.

After further tests I could localize the distortion problem to one and a half octave, exactly the tones which I had edited. But I had forgotten to reloop them after editing. Then I made several corrections at the release samples yet and now they sound acceptable.
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Re: Samples slightly distorted

Postby tf11972 » Sun Mar 19, 2017 2:16 pm

Again I have a problem, now with another overblowing flute:

When I play adjacent notes one after another within a semitone, the second note is always fluttering a second until it's stable. When I play wider intervals this issue doesn't occur.

I have tried to disable harmonic shaping filters (the rank is not enclosed), also the windmodel and all other parameters in the organ preferences, but it doesn't solve the problem. The samples were about a second too long at the end and I have shortened them, but this doesn't show an effect too.

Thanks in advance and best regards.
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Thomas

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