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 Forum index » DIY Hardware and Software » Developers' Corner
Octotone_ Can this be done?
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djthopa



Joined: Jul 22, 2013
Posts: 8
Location: madrid

PostPosted: Mon Sep 02, 2013 5:20 am    Post subject: Octotone_ Can this be done?
Subject description: looking for a frequency shifter for chord, pads, etc
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Hi everyone,

I was wondering if there is a module out there that can do pitch shifting by octaves and semitones.

Lets say you have four Vco´s all tuned to the same Frequency.(or not)
Four outputs of the module go into each of the Vco´s 1V/Oct in.
In the module you have 4 buttons for each column. And there are 4 Columns.
2 buttons are + / - 1 Semitone.
2 Buttons are +/ - 1 Octave.
There is 2 displays for each column, representing the values.

Also, pitch can be independent between columns or related to a master input.

This way you could dial chords, pads etc. I know the Flame Chord Machine or the Topobrillo Quantimator can do something like this, but they are based on presets.

It would be something like this:


Posted Image, might have been reduced in size. Click Image to view fullscreen.

Sorry for the crappy graphics.

Any ideas of how to make this possible?

Any suggestions will be greatly appreciated!

Thanks
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JovianPyx



Joined: Nov 20, 2007
Posts: 1247
Location: West Red Spot, Jupiter
Audio files: 161

PostPosted: Mon Sep 02, 2013 8:21 am    Post subject: Reply with quote  Mark this post and the followings unread

First - in the Subject description line, you have "frequency shifting". Then in the body, you use the term "pitch shifting". These are quite different, frequency shifting involves shifting the frequencies of a signal (including all of the harmonics) by a certain number of Hertz. This action detunes the harmonics away from their standard ratios against the fundamental.

That said, I think that you do, in fact, want pitch shifting which involves changing the frequency of the fundamental while the ratios of the harmonics remain the same.

I'm not familiar with the synths you mentioned, but voltage offsets are used all the time in expo (or v/oct) modular synths. To raise a pitch by one semitone, you add 1/12 volt to the pitch CV. To raise it a fifth, you add 7/12 volts and to raise it by an octave you add 1.0 volts. All of this is easy to do with OpAmps.

So if I understand what you want to do, then yes, it can most certainly be done and it is not horribly complicated. Adding voltages is done with a circuit called a "summer". Subtracting is also done with a summer, except that the subtracted voltage is just a negative voltage. An example would be to lower the pitch by one semitone, you would want to subtract 1/12 volt, OR you would add -1/12 volt. Some reading about opamps and voltage summing circuits (also called a DC mixer) will help you get started.

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Last edited by JovianPyx on Mon Sep 02, 2013 9:04 am; edited 1 time in total
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PHOBoS



Joined: Jan 14, 2010
Posts: 1795
Location: Moon Base
Audio files: 351

PostPosted: Mon Sep 02, 2013 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

My modified version of the MFOS oscillator calibration tool might help you out
a bit. It basically is an octave switch (steps of 1V) with up/down buttons (and
an auto mode). If you sum the output with an external (the original) CV you
have the octave part. This one goes from 0 to 7 volts, so it will only go
up. But if you sum it with a negative offset voltage it can go up and down
over a range of 7 octaves. You can find my version here Cool

You can also make a less complicated version with rotary switches, resistors
and some opamps.

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http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
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