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Old 07-29-2018, 05:48 PM   #1
Time Waster
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Default ReaRack3 Modular Synth Development (was 'Using Audio as a Control Signal')

Over on this thread https://forum.cockos.com/showthread.php?t=181406 there has been a bit of discussion about using audio channels for communicating control messages. AFAIK there is no standard for this. The first question that arises is should the control signal value be 0 to 1 or -1 to 1?

The advantages of using 0 to 1 is that 0 is the natural 'off' state for an audio signal and, although fairly trivial, the coding is is a bit easier and more intuitive.

The advantages of using -1 to 1 are higher resolution and you can use control signal output directly as sound signal if desired.

Initially I was leaning towards using -1 to 1, but I'm now thinking that 0 to 1 may be the best choice.

I would be interested in hearing opinions as to which method is best and whether there are any precedents that could be learned from?
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Old 07-29-2018, 09:47 PM   #2
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AFAIK; for analog synth there is a standard defining 0..1V so this is consistent to 1.0000 = 0dbV = 1 V, 0 = -inf dBV = 0 V.

With OSC, mostly parameters are encoded 0.0 .. 1.0.

it might be worth considering that in many cases control signals result in exponential effects, coded in dB or volt / octave.

-Michael
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Old 07-30-2018, 09:14 AM   #3
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In hardware, I've only seen 0...1 VDC and 0...10 VDC control voltages. 1V for synths and VCA's. 10 V for lighting. There are still some old solutions out there that use 1...2.3 VDC for VCA.

Mind you, that's DC. No negative values. Most audio interfaces can't output DC. The only exception that I know of, is RME's headphone outputs that can really output DC. I've used it with a FF400 and a FF800.

I suspect inside a DAW, you could use negative values. But I can't immediately see an obvious advantage...
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Old 07-30-2018, 04:54 PM   #4
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The idea is that we would be using the audio routing system for sending control signals within the DAW, in other words, just sending a varying stream of numbers. We would not be converting the the signal to an analog voltage for use with hardware, so that's not really a consideration.

The driver for this is that there is talk about implementing a 'wire' view for audio routing, and for FX, this could be used to emulate a 'patch lead' view for connecting up modules.

What I'm thinking of doing is to provide an option in ReaRack for using audio channels for communicating modulation control signals between modules. My idea is that this could be used either exclusively, or in conjunction with MIDI as the communication protocol. Hence I would like to get some consensus on a standard for using audio in this manner before I start on it.

So far it seems it is more intuitive to use 0 to 1, so I think that's probably the best choice, but I will leave it open for a while for further discussion before I commit to it.
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Old 07-30-2018, 07:43 PM   #5
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There is a SMPTE LTC reader thingy in your JSFX. If not, see old version here: http://www.1014.org/shiz/code/smpteltcreader
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Old 07-30-2018, 09:07 PM   #6
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DC offset is not the issue. The issue is, do we want to use the full available range of values (-1 to 1) or do we just want to use the positive values?

Another issue is that within the DAW we can use values far in excess of the -1 to 1 range because reaper uses 64 bit for internal processing, whereas the -1 to 1 range is 24 bit, if I understand it correctly. I propose that the comms signal would be hard limited to whatever range we choose, to avoid unexpected behavior.
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Old 07-30-2018, 09:38 PM   #7
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Quote:
Originally Posted by Time Waster View Post
The driver for this is that there is talk about implementing a 'wire' view for audio routing,
In fact in the pre-release forum Cockos showed a "proof of concept" implementation of such a "wire view" of the audio routing routing between tracks in Reaper. This provoked excitement of a lot of Reaper users.

Of course it would be viable to extend this alternate view to the routing within an FX chain and hence usable for ReaPack.

Of course it would be viable to extend this alternate view to the Midi routing and hence usable for ReaPack "as it is".

Both is discussed in detail in the pre-release forum and IMHO it's not unlikely that this is going to happen on the long run.

But as Midi routing supposedly will not be ignored, I don't see that this should drive a move of ReaRack's functionality.

-Michael

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Old 07-31-2018, 12:07 AM   #8
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Quote:
Originally Posted by Time Waster View Post
The idea is that we would be using the audio routing system for sending control signals within the DAW, in other words, just sending a varying stream of numbers. We would not be converting the the signal to an analog voltage for use with hardware, so that's not really a consideration.
Oops. Sorry. Just disregard the remarks about hardware.

Could an option to send CV to hardware outputs be interesting for some?
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Old 07-31-2018, 01:33 AM   #9
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Quote:
Originally Posted by cyrano View Post
Could an option to send CV to hardware outputs be interesting for some?
I think it would be, but there are already MIDI to CV converters for that (hardware) AFAIK. Not sure if you can do that with software? Would need to look at audio outlet specs vs CV specs, but I suspect they would not be compatible
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Old 08-14-2018, 04:26 PM   #10
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Quote:
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Oops. Sorry. Just disregard the remarks about hardware.

Could an option to send CV to hardware outputs be interesting for some?
Hi ! it would be useful but Isn't there plugins for this? i think i have seen, but not in reaper i think
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