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Using the Velocity output of a MIDI CV module
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THeff



Joined: Sep 01, 2006
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PostPosted: Fri May 01, 2009 8:59 pm    Post subject: Using the Velocity output of a MIDI CV module Reply with quote  Mark this post and the followings unread

Hi all,

I have built several MIDI CV modules that have a velocity output, but I have never really used the velocity. Just mixing the ADSR and Vel voltages together is not a workable solution. It seems to me that the velocity voltage needs to control the amplitude of the ADSR output to be effective and maintain the timbre.

In thinking about this my first thought is that it would require a DC input VCA controlled by the velocity voltage and passing the ADSR voltage to the audio VCA. This seems rather complicated.

Recently I was thinking that another way to do it, is to have the velocity voltage feed the high side of the Sustain pot instead of the fixed +15V that is typically used in the ADSR module. This would at least allow the amplitude of the Sustain, Decay, and Release to be set by the velocity voltage. This would not control the amplitude of the Attack voltage though.

Anyone have any thoughts on this? Am I over complicating this?

Regards,

-Tim
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Sat May 02, 2009 4:56 am    Post subject: Reply with quote  Mark this post and the followings unread

You'd want to multiply the signals, not add them. The easiest way to go would be to ad another VCA in series, one getting the envelope the other getting the velocity voltage. (a VCA really is nothing but a multiplier circuit)
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Jan
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THeff



Joined: Sep 01, 2006
Posts: 216
Location: Florida
Audio files: 30

PostPosted: Sat May 02, 2009 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Jan,

What you said makes sense, using the two VCA's in series, in the audio path.

I mentioned using two VCA's, but I guess my brain wanted to have the 1st VCA controlled by velocity to set the level of the CV of the ADSR and then route that CV to the 2nd VCA.

So one VCA would be operating on the CV and the 2nd would be operating on the audio.

I was hoping there was a simple way to do it without have to use two VCA's. I have not tried anything yet, I'm just fishing for ideas. I am going to modify a TH ADSR with the Sustain voltage to see how that feels.



-Tim


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Blue Hell
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PostPosted: Sat May 02, 2009 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

THeff wrote:
I mentioned using two VCA's, but I guess my brain wanted to have the 1st VCA controlled by velocity to set the level of the CV of the ADSR and then route that CV to the 2nd VCA.


Must admit that I had read over it ... but both solutions are equivalent ... as in (a x b ) x c == a x ( b x c) == a x b x c.

It depends a bit on the actual envelope generator's design if modulation of the sustain voltage would do the same thing, but it just might ... let us know how you fare!

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