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Midi-cv Converter?

Posted: Sun Jun 21, 2009 8:55 pm
by Gregor Samsa
I'm looking into SH-101's for which I will also need a midi-cv converter. Can you give me some options for one that will work solidly, but won't kill my bank account? I don't see myself running lots of analogs so I don't need tons of in's/outs/whatever. I just want to be able to play it and get it into my sequencer.

Re: Midi-cv Converter?

Posted: Sun Jun 21, 2009 8:57 pm
by cornutt
The absolute cheapest way to do this is probably the Synhouse Midijack. Very basic, and you have to install it yourself, but everything I've read says it works.

Re: Midi-cv Converter?

Posted: Sun Jun 21, 2009 10:11 pm
by madtheory
This should be a sticky- "Kenton Pro Solo II: world's best MIDI CV"

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 12:53 pm
by gnasher
This is an extremely naive question. But, what does a MIDI - CV converter do? How would you use it?

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 1:00 pm
by Syn303
gnasher wrote:This is an extremely naive question. But, what does a MIDI - CV converter do? How would you use it?
A MIDI > CV Converter basically allows you to control or sequence analogue gear from midi sources or even your PC.

examples:

MIDI Synth > CV Converter > CV & Gate outs > Analogue Synth CV & Gate Ins.

MIDI SEQ > CV Converter > Din Sync24 Out > Roland Din Sync24 In (stop/start messages for a drum machine or seq 303/606/808/909)

PC > CV Converter > CV & Gate Outs > Analogue Synth CV & Gate Ins (same with sequencers/drum machines)

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 8:50 pm
by cornutt
gnasher wrote:This is an extremely naive question. But, what does a MIDI - CV converter do? How would you use it?
There are two signals that an analog synth, in a conventional VCO-VCF-VCA patch, absolutely has to have in order to play recognizable notes:

* A control voltage, which sets the pitch of the VCO.

* A gate signal, which starts and stops the envelope generator.

A basic MIDI-CV converter takes a MIDI Note On message and produces these two signals. It raises the gate signal when the Note On is received; this goes to the envelope generator and starts the attack phase. It extracts the note value from the Note On and converts that to a voltage level, for the VCO control voltage. When a MIDI Note Off message is received, it lowers the gate signal, which causes the envelope generator to advance to the release phase.

More sophisticated MIDI-CV converters can do more things. For example, it can extract the velocity value from the Note On message and produce a control voltage from it, which is conventionall routed as an additional control signal to the VCA and makes the note play louder or softer. It can take MIDI Pitch Wheel messages and use that to modify the VCO control voltage, so that it responds to pitch bend. Or it can transform MIDI Controller messages into additional control voltages.

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 9:40 pm
by gnasher
Oh I think I've got it. So it enables an analogue synth (without MIDI i/o) to be controlled by an external master MIDI controller?

But, doesn't every manufacturer have different configurations when it comes to this CV business? If yes, is there some sort of list that shows which keyboards respond to which 'messages' or am I over analysing a bit? Sorry for all the questions but does CV stand for constant velocity or is that something entirely different?

Thanks for enlightening me guys.

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 10:12 pm
by steveman
gnasher wrote:Oh I think I've got it. So it enables an analogue synth (without MIDI i/o) to be controlled by an external master MIDI controller?

But, doesn't every manufacturer have different configurations when it comes to this CV business? ... .... Sorry for all the questions but does CV stand for constant velocity or is that something entirely different?
CV stands for Control Votage. Most synths respond to 1v/ oct ie. if the pitch voltage rises by 1v the pitch of the synth should rise by an octave. Yamaha and earlier Korgs synths used Hz/volt. Buchla modular synths use 1.2v/oct. Given the cost of these it's unlikely to be a problem for most of us. Virtually all MIDI > CV convertors will allow you to select which type of output they give.
Gate signals can be either positive or negative, some synths respond to say a 5v trigger, another may need 10. Easiest way is to send the highest voltage then most things will work. (BTW highly unlikely to cause damage with too higher voltage). Moog used something called an s-trigger which I think is essentially inverted. I've heard 1 or 2 older synths respond to different gate levels, but I'm not convinced.
All this is taken care of in the MIDI > CV converter.
If yes, is there some sort of list that shows which keyboards respond to which 'messages' or am I over analysing a bit?
The older synth knows nothing about any messages. All it has are a pitch CV input, a gate input, and if you're lucky a filter CV input.
What 'messages' it responds to are entirely up to the converter. Velocity &/or mod wheel to filter CV are obviously useful.

Re: Midi-cv Converter?

Posted: Tue Jun 23, 2009 10:45 pm
by premieklovn
I second the Kenton Pro Solo MKII. It's lovely!

Re: Midi-cv Converter?

Posted: Wed Jun 24, 2009 4:43 am
by cornutt
steveman wrote:Moog used something called an s-trigger which I think is essentially inverted.
It's weirder than that. The S-trigger is a completely different type of circuit. The sender of the signal doesn't apply any voltage to the circuit; it just switches a "dry" switch (actually a transistor) that either grounds out the line or not. In order to sense the state, the receiver of the circuit must apply a pull-up voltage to the line.
I've heard 1 or 2 older synths respond to different gate levels, but I'm not convinced.
Some older Rolands have low-impedence gate inputs that reqiure more current to drive. IIRC, the Yamaha CS series need inverted gate.

Re: Midi-cv Converter?

Posted: Wed Jun 24, 2009 12:42 pm
by gnasher
Thanks very much guys. I think I've got it now...and I've just realised that I don't even need one of these converter things.

Re: Midi-cv Converter?

Posted: Wed Jun 24, 2009 10:39 pm
by Gregor Samsa
How difficult is the midijack to install? I looked at the synhouse site and it seems to indicate being a bit involved.

The kenton is listed at $236.00 on ebay- is that what you would consider a decent price for one in which I won't have to install? That's looking like the way to go for me.

Re: Midi-cv Converter?

Posted: Thu Jun 25, 2009 2:57 am
by cornutt
Gregor Samsa wrote:How difficult is the midijack to install? I looked at the synhouse site and it seems to indicate being a bit involved.

The kenton is listed at $236.00 on ebay- is that what you would consider a decent price for one in which I won't have to install? That's looking like the way to go for me.

Yeah, the Midijack looks like some work -- it depends to an extent on the synth you're putting it in. That's a good price on the Kenton; I'd go for that.

Re: Midi-cv Converter?

Posted: Thu Jun 25, 2009 4:57 am
by Gregor Samsa
That's what I'm going to do- I don't want to risk ruining the synth.

Which cables do I need to get to fit it w/ the sh? It seems from looking around that 1/4" patch cables do the trick?

Re: Midi-cv Converter?

Posted: Thu Jun 25, 2009 8:32 am
by steveman
Not as sophisticated as the Kenton but the BassStation Rack has MIDI > CV built in (also CV > MIDI!). Got mine for £100, and you get a free Synth :)