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 Forum index » Clavia Nord Modular » G2 Patches - Completed » FX
High end DIY stereo pitch shifter
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1038
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 213

PostPosted: Fri Jun 11, 2010 8:59 am    Post subject: High end DIY stereo pitch shifter
Subject description: offers control over delay size and crossfading
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As the title says. I've been meaning to build this for a while. Some questions from 3phase in another thread re-sparked the interest. This is based on the "classical" pitch shift design which has been around for a long time. A true granular approach (offering pitch jitter and other goodies) is something I might try next. (Update: Done. arrow http://www.electro-music.com/forum/topic-42431.html )

It offers control over delay size (maximum 500ms) and cross-fading. I also threw feedback in there, as that is an effect I'm very fond of.

The pitching is very accurate due to using LFOs which have excellent exponential tracking. By up-sampling their crude control signals to audio-rate, the best possible sound quality is achieved.

In order to implement controllable delay size, a very precise logarithmic function is necessary. Unfortunately the level scaler module in 6dB roll-off isn't precise enough for this, skewing the tuning quite noticeably when the delay size is changed. I devised a workaround which is rather expensive DSP-wise and also has the drawback that the pitch shifter has to "restabilize" into the new delay length setting after it has been changed. This means that the delay size is manually adjustable, but not modulatable in realtime. However, the tuning is dead on, regardless of delay size or pitch shift amount. Smile

It's a very precise design and sounds as good as it gets. But it's rather expensive, so not really a building block.

cheers
t

Addendum: I've noticed that the feedback loop isn't stable as it is, as DC offsets or nasty HF oscillations can build up. I added stabilizing HP and LP filters.

Important update! There was a omission with the control-rate to audio-rate conversion, causing a minute glitch. I reworked the patch. All old versions have been replaced. Attached below is the new version.


DIYPitchShift_TK.pch2
 Description:
offers control over delay size and crossfading. feedback too.

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 Filename:  DIYPitchShift_TK.pch2
 Filesize:  3.78 KB
 Downloaded:  625 Time(s)


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Last edited by Tim Kleinert on Fri Jun 11, 2010 2:56 pm; edited 2 times in total
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1038
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 213

PostPosted: Fri Jun 11, 2010 2:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

I thought I'd bump this, as there has been an important improvement.
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