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 Forum index » DIY Hardware and Software
Is there such a thing as a digitally controlled ADSR?
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jackdamery



Joined: Apr 26, 2010
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PostPosted: Thu Jan 17, 2013 11:53 am    Post subject: Is there such a thing as a digitally controlled ADSR? Reply with quote  Mark this post and the followings unread

I was wondering if any chips or designs existed for a digitally controlled ADSR. I'd like to stick such a thing on my vco to save building one from components.
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jackdamery



Joined: Apr 26, 2010
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PostPosted: Thu Jan 17, 2013 11:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Now I think about it, I suppose in essence it would be a digitally controlled amplifier.
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minisystem



Joined: Nov 16, 2012
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PostPosted: Thu Jan 17, 2013 8:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do you mean something like this?

http://www.electricdruid.net/forums.html?page=projects.envgen7

It's an ADSR implemented in software on a microcontroller. Takes gate/trigger as input and outputs a control voltage based on ADSR settings.
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bubzy



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PostPosted: Fri Jan 18, 2013 12:07 am    Post subject: Reply with quote  Mark this post and the followings unread

ive recently been messing about with a DAC on an arduino after reading elmegils post on the arduino subforum. with this method its quite attainable, and very configurable too.
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elmegil



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PostPosted: Fri Jan 18, 2013 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Speaking of which, I was just working on building a shield that has two MCP4922's and a few op amps for buffers. My original thought was to proceed on some of the MIDI->CV speculation I was doing a few months back, but I realized as I was going along that basically I'm creating a shield that could be used for envelopes or any other set of 4 CVs and two square signals (gate & trigger for the MIDI application). Quadrature LFO came to mind too.

Unfortunately it's just a proto shield with wires running every which way; I have not made any headway with eagle doing actual boards, but I will share the circuit when I'm done (it's really pretty simple, so...).
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rjh



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PostPosted: Sun Jan 20, 2013 5:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Not sure about digitally controlled amplifiers, but there are digital controlled potentiometers (SPI or I2C). I haven't experimented with it but I guess it could potentially be used in a simple op-amp amplifier configuration to create a DCA. I know at least Microchip and Analog Devices makes them.
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elmegil



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PostPosted: Sun Jan 20, 2013 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

I bought some of the microchip ones, 10K, from SparkFun a while back. It's an MCP4131-103. They also have 5k, 50k, and 100k variants.

One unfortunate thing is they only have an operating voltage up to 5.5V which will make them more difficult to use in the typical 12V or 15V synth circuit.
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rjh



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PostPosted: Sun Jan 20, 2013 8:05 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:

One unfortunate thing is they only have an operating voltage up to 5.5V which will make them more difficult to use in the typical 12V or 15V synth circuit.


That's good to know. Looked up some other ones and it seam to be the same. Maxim makes a few that can handle 8v but not more. Though I'm guessing if you're working in the digital domain to begin with you're probably working in the 0-5v range.
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bubzy



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PostPosted: Sun Jan 20, 2013 8:32 am    Post subject: Reply with quote  Mark this post and the followings unread

thats not a problem at all,
use an op amp and boost the voltage up 3x
0-5 becomes 0-15.

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rjh



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PostPosted: Sun Jan 20, 2013 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

more importantly scale / offset the signal first. Not very hard, but inconvenient Smile
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JovianPyx



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PostPosted: Sun Jan 20, 2013 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

digital stuff is tending toward lower and lower voltages. I see lots of applications where 3.3volts is the standard. I see more and more digital parts that are 2.2v. Lower voltage digital circuits tend to use less power and are usually faster because the signals have less "distance" to travel when changing state.

As bubzy said, when it gets to a place where the outside world wants to see higher voltages, then amplify.

I mess with dsPICs at 3.3 volts. The DACs barely output 1 volt. So I amplify. Some people freak out about amplifying because there's always a bit of noise - but hey show me any noise free circuit and you win a prize. If the noise is low level enough that you don't hear it, then it doesn't matter. Yeah, it's another part to purchase and solder. Yep. Oh well. With SMT, you can cram all kinds of crap on a board now unlike the old days when you could actually see the parts you're soldering...

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elmegil



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PostPosted: Sun Jan 20, 2013 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Didn't mean to say they were a LOT more difficult Very Happy
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JovianPyx



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PostPosted: Sun Jan 20, 2013 5:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

To answer the OP's question "Is there such a thing as a digitally controlled ADSR?"

The PAiA Fatman has a hybrid digital/analog ADSR and ASR. The ramp generating parts are capacitors and resistors while the level sensing logic parts are actually code running in the MIDI controller microprocessor.

I have also personally written code to be an ADSR within a digital design without any analog help.

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FPGA, dsPIC and Fatman Synth Stuff

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The Real MC



Joined: Jun 20, 2008
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PostPosted: Mon Jan 21, 2013 3:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

The Moog Source has digitally controlled ADSRs, OTA based circuits using only two CVs for transition time and level.

http://www.retrosynth.com/~analoguediehard/studio/keyboards/moog_source/index.html#technical
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