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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Noise Toaster Attack Decay Generator Control Voltage?
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Just Say Noise!



Joined: Nov 14, 2011
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Location: Portland, Oregon

PostPosted: Sun May 05, 2019 12:45 pm    Post subject: Noise Toaster Attack Decay Generator Control Voltage?
Subject description: Convert audio into a control voltage question
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Been a while since I've posted. I'm trying to figure out how to convert an audio signal (drum machine, mp3 player etc) into a voltage that can activate the Attack Decay Generator in the Noise Toaster. Ideally, I want to plug in an external audio source, have a pot to adjust the sensitivity of the incoming signal, and hear the AD Gen bounce along with the audio. I thought it would be pretty simple since the AD Generator just needs a positive voltage gate to work. However, its proving to be more of a challenge than I imagined.

A few of the problems I'm encountering here:
An audio signal from a CD player or drum machine is around 1v, as I understand. The AD Generator in the Noise Toaster needs at least 7 to 9v in order for it to create the gate, as I understand. So plugging the audio source directly into the AD Gen at S10 (the manual gate) does not work.

Some things I tried here:
I've tried a Comparator (LM324 and TL072 i think) but had no luck. It seemed to be always outputting a voltage even with no audio source.

I tried amplifying the audio signal via a 4049 to boost the voltage, then sending it through a scmitt trigger 74c14 to square it up, but that did not result in a clean gate that bounced along with the drum machine audio.

Also tried a simple LM324 non-inverting amplifier to boost the voltage, but also not really working. Does anyone have any experience doing this?

Here is pic of the AD Gen from the Noise Toaster. I assume an audio input CV would need to enter at S10...


AD GEN.jpg
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Just Say Noise!



Joined: Nov 14, 2011
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Location: Portland, Oregon

PostPosted: Sun May 05, 2019 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Forgot to mention, I'm not trying to hear the external audio signal through the noise toaster, just use it as a voltage source.
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PostPosted: Sun May 05, 2019 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just some gratuit rambling without too much thought ...

This seems to be designed to generate an envelope .. .. hmm how would that fit to track audio beats .. it would need some pre-processing then .. as in .. an envelope follower with some level detection after it .. or just an envelope follower by itself .. but the latter case could not make a shorter decay than the audio has .. so an envelop follower with a level detector and then an envelope generator seems to be what is needed.

?

Hm and maybe some compression .. but that might just muddify things instead.

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also .. could someone please turn down the thermostat a bit.
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Just Say Noise!



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PostPosted: Sun May 05, 2019 7:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
.. an envelope follower with some level detection after it ..


That may work. What do you mean by level detection?

Ultimately, I want the S10 manual gate button to be voltage controlled. So every time there is a peak in the audio, it would trigger the envelope generator (like tapping the S10 manual gate button every time there is an audio peak). If there was a sustained peak in the audio, then it would be like holding the S10 manual gate button down until the audio peak drops.

I'll look into some envelope follower circuits. As long as the follower outputs close to 9 volts it should work.

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Grumble



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PostPosted: Sun May 05, 2019 10:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

What I would do:
1st - a banpass filter set to the main frequency of the beat/signal you want to sync to
2nd - rectify this signal
3rd - low pass filter followed by a comparator of which you can set the tripping level
4th - attack (sustain) decay circuit

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Just Say Noise!



Joined: Nov 14, 2011
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Location: Portland, Oregon

PostPosted: Tue May 07, 2019 6:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Good ideas. Starting to get the picture.

Quote:
1st - a bandpass filter set to the main frequency of the beat/signal you want to sync to
2nd - rectify this signal
3rd - low pass filter followed by a comparator of which you can set the tripping level


Why would I need to send the signal through a low pass filter if its already been isolated by the bandpass filter?

The comparator suggestion makes sense to me. I tried building this MFOS interface circuit (boostlowgatetriggervoltage2), but it didn't seem to track the audio signal. I'll have to breadboard it again. Grumble mentioned "setting the tripping level" on the comparator. Is the tripping level set by the 100k and 20k resistors on pin 2? Is it possible to make the tripping level adjustable with a pot? If so, would the pot go where the 100k resistor on pin 2 is?

Thanks for pointing me in the right direction!!


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Grumble



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PostPosted: Tue May 07, 2019 9:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Why would I need to send the signal through a low pass filter if its already been isolated by the bandpass filter?

Because after rectifying you have (positive pulses in the frequency double that of the bandpassfilter frequency.

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tinfoilcat



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PostPosted: Thu May 09, 2019 12:24 am    Post subject: Reply with quote  Mark this post and the followings unread

You might want to try Rays Guitar to gate circuit: http://musicfromouterspace.com/analogsynth_new/HOT_TIPS/guitartogate.php Lowering the gain would be a good idea I guess.

Trigger for soundlab: http://musicfromouterspace.com/analogsynth_new/SOUNDLABMINISYNTH/guitartrigger/guitartrigger.html
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PostPosted: Fri May 10, 2019 8:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
You might want to try Rays Guitar to gate circuit: http://musicfromouterspace.com/analogsynth_new/HOT_TIPS/guitartogate.php


That looks promising. Don't know how I missed that schem. Thanks for the tip. Will breadboard it up.

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PostPosted: Mon May 13, 2019 10:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just finished bread boarding Rays Guitar to Gate Circuit, and it worked nicely! Thanks for all the tips everyone! I didn't bother with the additional gain stage (U1-D), but may add that later to hear the audio signal as well. Of course, when I figure out one thing, it opens up more questions. I'll keep tweaking it in the meantime.

What is the purpose of the U1-B stage? additional gain? voltage follower? buffer? Its doing its job, but I'm trying to understand what that is.

Is there a way to keep the Guitar to Gate Circuit quiet when no input signal is present? For example, when there is no input signal at J1, and the gain sensitivity R2 pot happens to be all the way up, other unrelated oscillators in my synth are triggering the envelope generator. I can reduce the 1M resistor on U1-A so there is less gain and that fixes the false triggering, but is there another way?

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Grumble



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PostPosted: Mon May 13, 2019 11:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can lower the resistance of R6 but you also have to increase the capacitance of C2 to keep the frequency response.
For calculations: http://sim.okawa-denshi.jp/en/opampkeisan.htm

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