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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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 Posted: Fri May 22, 2009 11:58 am Post subject:
Electro-Harmonix HOG pedal
Subject description: How might it work |
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Hi Guys,
Well I am looking to try to knock something similar up using Kyma.
I have looked at the videos on the website and downloaded the manual.
As far as I can see/hear the generated voices are synth voices and not the guitar pitch shifted.
So if this is true then it must be extracting the frequency of the 6 strings somehow.
Or maybe I am wrong and it is some pretty clever pitch shifter.
What do you guys think?
Andy |
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jksuperstar
Joined: Aug 20, 2004
Posts: 2503
Location: Denver
Audio files: 1
G2 patch files: 18
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| Posted: Fri May 22, 2009 12:59 pm Post subject:
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The older microsynth used techniques similar to the roland GR-300. The fact that it's based on harmonic intervals, seems to me like it uses pitch shifting. After the envelope/VCA and filter are added, I'd guess that's probably were the synthetic sound comes from.
-- The Freeze is probably just stopping input to the pitch shift delay buffer, but continuing to read from it.
The POG at least sounds & plays like it uses a couple pitch shifters in parallel. |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Fri May 22, 2009 1:31 pm Post subject:
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Good point with the harmonic intervals.
Well my first attempts at polyphonic pitchshifting melt my pacaranas dsp at four voices, also the latency is too much to be useable.
Back to the drawing board. |
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jksuperstar
Joined: Aug 20, 2004
Posts: 2503
Location: Denver
Audio files: 1
G2 patch files: 18
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| Posted: Fri May 22, 2009 8:52 pm Post subject:
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| Do you have a copy of Curtis Roads' Computer Music Tutorial? There's some good material on these pitch shifting devices, and covers the two types the G2 has (freq shift & pitch shift). |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Fri May 22, 2009 10:47 pm Post subject:
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I do have the book, I will have a look.
I have been using realtime spectrum analysis (FFT based I think) and re-synthesis with sine oscillator banks. The simple pitchShifter in Kyma doesn't handle polyphonic signals very well. There is also a FrequencyScale module that I read about last night I am going to have a play with, maybe this will work a little better.
I have had some help about the DSP melting from the SymbolicSound forum, looks like a scheduling problem in Kyma is causing the issue, first thing I am going to try is to try fix this and see if it is useable.
Cheers
Andy |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Sat May 23, 2009 12:10 pm Post subject:
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| jksuperstar wrote: | | Do you have a copy of Curtis Roads' Computer Music Tutorial? There's some good material on these pitch shifting devices, and covers the two types the G2 has (freq shift & pitch shift). |
I have tested the G2 pitch shifting and freq shifting and as far as I can see they do not work with polyphonic material very well at all!
It seems the fft approach and resynth with oscillator banks using sine wavs seems to be a popular approach for polyphonic pitch bending. This is what I have been doing with Kyma
I have a Kyma patch that provides polyphonic pitchshift with the same number of voices as the HOG and it uses up nearly all the dsp on a Pacarana! It is fairly inefficient as I am using a module that pitchshifts the spectrum and then playing it with an oscillator bank, this is done for each voice.
I am thinking next of doing a fft, then processing copies of the fft in the freq domain, combining then and then doing a reverse fft. Unfortunately there is bugger all info on this in the Kyma manual even though the fft and inverse fft modules are available. |
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DrJustice
Joined: Sep 13, 2004
Posts: 2112
Location: Morokulien
Audio files: 4
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| Posted: Sat May 23, 2009 1:41 pm Post subject:
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| BobTheDog wrote: | | I have a Kyma patch that provides polyphonic pitchshift with the same number of voices as the HOG and it uses up nearly all the dsp on a Pacarana! It is fairly inefficient as I am using a module that pitchshifts the spectrum and then playing it with an oscillator bank, this is done for each voice. |
Does Kyma have a actual polyphonic pitch detector module (or as part of a poly pitch shifter module...), or did you roll your own? If the latter, how do you go about it? Wouldn't an inverse FFT be more efficient than an oscillator bank for the resynthesis?
DJ
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Sat May 23, 2009 1:53 pm Post subject:
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Nope I am using the Kyma one.
An invert FFT sounds like a much better idea, unfortunately there is no documentation on the FFT modules in the manual!
I can do the FFT, then the inverse FFT and get the original sound out but have no idea how to make copies, manipulate and combine the FFT data.
I will make a post on their forum.
Cheers
Andy |
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DrJustice
Joined: Sep 13, 2004
Posts: 2112
Location: Morokulien
Audio files: 4
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| Posted: Sat May 23, 2009 2:07 pm Post subject:
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| BobTheDog wrote: | | I can do the FFT, then the inverse FFT and get the original sound out but have no idea how to make copies, manipulate and combine the FFT data. |
Yes... the manipulation of the spectrum requires some 'free form' maths if you want to do your own things. I'd think this is a perfect example of where being able to write your own DSP code comes in handy, unless there's a rich selection of spectrum (or possibly just vector) processing modules that can be used.
DJ
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Sun May 24, 2009 8:57 am Post subject:
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Well I have a start with 10 voices using a delay line which uses 25% of a dsp but doesn't sound anywhere near as good as the Hog pedal or the dsp expensive osc banks.
I am still looking into the FFT stuff and have had some interesting effects from arseing around but have no idea how to pitch shift on the fft data in the frequency domain, anyone here know?
I might cheat a bit and start doing a version based on the poly audio from the guitar, I was thinking of creating synth voices by freq tracking the strings as a first step to see what that sounds like.
Its all fun anyway!
Andy |
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DrJustice
Joined: Sep 13, 2004
Posts: 2112
Location: Morokulien
Audio files: 4
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| Posted: Sun May 24, 2009 1:00 pm Post subject:
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| BobTheDog wrote: | I am still looking into the FFT stuff and have had some interesting effects from arseing around but have no idea how to pitch shift on the fft data in the frequency domain, anyone here know?
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One way is to obtain a frequency/magnitude spectrum by unwrapping the phases, manipulate the frequencies (and the magnitudes for a bit of filtering or convolution fancy pansy while you're at it  ), convert back to phase/magnitude and do your inverse FFT. I.e. :
FFT -> phase/mag -> freq/mag -> freq/mag manipulation -> phase/mag -> iFFT
For an excellent piece of reference code, have a look at Stephan Bernsee's smbPitchShift - you'll find a link in this thread - sorry for making it so convoluted (hah, a DSP pun!), but we have to create some traffic in the Developer's Corner, this is what it's made for after all  Also, a search on "Phase Vocoder" will probably produce some useful references too.
| Quote: | | Its all fun anyway! |
Pacarana fun? You gotta be kidding 
DJ
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Last edited by DrJustice on Sun May 24, 2009 5:18 pm; edited 1 time in total |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Sun May 24, 2009 1:58 pm Post subject:
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| Thanks DJ, will look at the code tomorrow with a fresh head. |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Mon May 25, 2009 12:07 am Post subject:
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Well I don't think a fresh head is going to help me here!
My understanding of Kyma is far to basic to reproduce this.
I think I will have to wait until my brain gets up to speed with Kyma or if the sdk comes out. |
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GovernorSilver
Joined: Apr 26, 2004
Posts: 1349
Location: Washington DC Metro
G2 patch files: 1
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| Posted: Tue May 26, 2009 3:17 pm Post subject:
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Much respect to you, Andy, for at least making an attempt at it.
Don't kill yourself, though.
Sounds like it would be a lot easier to just run a real HOG pedal into a Kyma if one wanted to integrate the HOG sound with something else going on within Kyma.
_________________
Current and recent work on Soundcloud
Some old stuff on VIRB |
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BobTheDog
Joined: Feb 28, 2005
Posts: 4044
Location: England
Audio files: 32
G2 patch files: 15
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| Posted: Tue May 26, 2009 3:52 pm Post subject:
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I'm getting there, I have about 7 versions now each getting a little better.
When I have something worthwhile I will post details and sounds.
Andy |
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