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 Forum index » Clavia Nord Modular » G2 Patches - Experimental
wavecycle-based pitch shifter
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1027
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Tue Jun 24, 2008 1:53 pm    Post subject: wavecycle-based pitch shifter
Subject description: a different approach to pitch shifting
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Rather than using delays and crossfading, this pitch shifter recognises individual waveform cycles of the incoming audio, compresses or stretches them and realigns them along the time axis. When compressing (pitching upwards), accumulating gaps in the time axis are intelligently filled with duplicate cycles. When stretching (pitching downwards), the resulting time overhead is compensated by skipping wavecycles. The result is an artefact-free pitch shift. Smile

However, it works strictly only for monophonic audio, and only for simple, clean waveforms without too strong higher harmonics or inharmonic content (or noise). You'll notice this if you raise the filter resonance of the demonstration audio source. With increasing resonance, the pitch tracker has increasing difficulty to latch on, producing clicks and artefacts in the pitch shifter. This is due to the sub-par pitch detection possibilities on the G2, either DIY or module. (Proper autocorrelation-type pitch recognition is impossible to patch on the G2.)

I first thought about posting it in the building blocks section, but as it is not really usable due to its design and deficiencies (or maybe it is?), I put it here in the experimental section as a sort of study object.

best,
tim


CycleShifter TK.pch2
 Description:
wavecycle-based pitch shifter, a different approach to pitch shifting

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 Filename:  CycleShifter TK.pch2
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Blue Hell
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Joined: Apr 03, 2004
Posts: 20558
Location: The Netherlands, Enschede
Audio files: 147
G2 patch files: 318

PostPosted: Tue Jun 24, 2008 2:46 pm    Post subject: Re: wavecycle-based pitch shifter
Subject description: a different approach to pitch shifting
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tim wrote:
strictly only for monophonic audio, and only for simple, clean waveforms without too strong higher harmonics or inharmonic content (or noise).


It makes nice warbled choirs from polyphonic complex dirty waveforms with strong higher harmonics and inharmonic content Shocked

Sand in the machine ... nice patch Exclamation

Now if only I'd know how it worked ...

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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1027
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Tue Jun 24, 2008 3:11 pm    Post subject: Re: wavecycle-based pitch shifter
Subject description: a different approach to pitch shifting
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Blue Hell wrote:
Now if only I'd know how it worked ...


Yeah, I don't understand half of it myself anymore. Rolling Eyes Laughing No, honestly, with this kind of stuff, I find myself having to backtrack cable by cable, module by module, to get back into the line of thought that produced the patch.

In a nutshell, all this stuff is based on audiorate counter circuits. There is a finely calibrated counter that moves along with the delay line readout pointer, giving accurate access to the audio material. Another counter measures the length of the incoming wavecycles. Yet another counter features exponential tracking and is in charge of pitch shifted playback of individual wavecycles. The difficult thing is making these circuits interact with each other in order to produce the desired functionality. Simply put, the playback counter plays back a specific wavecycle until the measuring counter tells it that a new complete wavecycle is ready to be fetched. So, when pitching up, the played wavecycles will be shorter, causing the playback counter to eventually loop a wavecycle because there isn't a new one available yet. When pitching down, the playback will take longer than the average wavecycle length, and will eventually skip over a wavecycle. This is the basic concept.

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Joined: Jun 21, 2003
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PostPosted: Tue Jun 24, 2008 3:27 pm    Post subject: Re: wavecycle-based pitch shifter
Subject description: a different approach to pitch shifting
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Blue Hell wrote:

Now if only I'd know how it worked ...


Jan, that's a scary comment. I thought you knew the G2 inside out Shocked such comments from an Admin scare the living s**t out of novices like me Rolling Eyes

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Blue Hell
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PostPosted: Tue Jun 24, 2008 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hm, gentlemen, yes, I see Laughing
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Tim Kleinert



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Location: Zürich, Switzerland
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PostPosted: Fri Jun 27, 2008 3:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Laughing
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