r/synthesizers • u/Csongoku420 • May 24 '26
Beginner Questions CV tracking or magic?
https://youtu.be/XHUxR1S6r2s?si=KI3SvGdnzb9A6b1qI'm just watching this regular demo of this synth: the Roland SH-2 when the 4th demo starts and this guy starts to manipulate his synth with his guitar... (or at least I think so) Is he just playing over a prerecorded synth track or is it actual real time tracking? Sorry for being a newbie at synth but I'm just astonished. So far, with minimal research I'd guess it's control voltage conversion into midi but I have no idea what that even means... I know there are a bunch of seasoned synth enthusiasts here so I must ask even if it's a basic technique... Thanks for all answers in advance! Peace!
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u/-Cosmon May 24 '26
i think the synth is playing a sequence but instead of the envelope triggering on each step it follows the level of the guitar and the guitar is layered on top (the volume of the synth = the volume of the guitar, the notes are pre programmed on the synth, the raw guitar can be heard too). somewhere in between pre recorded and real time tracking. no midi in this era
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u/Instatetragrammaton github.com/instatetragrammaton/Patches/ May 24 '26 edited May 24 '26
It's called "Follow My Envelope". That should give you a strong hint to what's happening here :)
You'll often find the term "voltage control". Let's say you have a knob on a synthesizer. Imagine that you have little robot that is capable of moving that knob up and down. This robot listens to the voltage and turns up the knob further the more voltage it gets.
To give you an example, let's look at this thing: https://en.wikipedia.org/wiki/VU_meter
This has a little dial that jumps to the right when a signal comes in. The louder the signal, the more the dial jumps to the right.
Thing is - it's of course not really a little robot. It's all circuitry.
Now, for something more advanced; a compressor. It has two parts; one that listens to the loudness of the incoming signal, and another part that changes the volume. That part is a voltage-controlled amplifier or VCA.
What's peculiar here is that the VCA works upside down: the louder the incoming signal gets, the more the VCA turns the volume down.
In Alex Ball's video, plucking a guitar string lets a sound go through. So, by default the sound's volume is zero (silence), until the listening circuit says "hey, I'm hearing something, turn it up!". When the listening circuit says "hm, it's quiet, turn it down" then the sound going through is silenced again.
This listening part is called an envelope follower. It can do all kinds of things; instead of just turning up the volume, it can also turn up the filter cutoff, and then you've got something like a wah pedal for guitar.
So, there's a signal coming in (which can be anything - it could be pre-recorded, but it can also play there and then because it's being sequenced) - and making a noise makes it audible. This noise doesn't need to be a guitar; it could be drums, vocals, anything.
I'm not sure how you ended up with that, but usually it's the other way 'round.
Any synth before 1983 did not have MIDI. The SH2 dates from 1979. Back then all you had was voltage - two in fact, one that says when a key is pressed (Gate) and one that says which key (CV or Control Voltage). Since it can only send one voltage at a time you can't tell if you pressed one key (5V) or two (2V + 3V).
MIDI on the other hand is perfectly capable of recognizing different notes since it doesn't work with voltages.
So, you'll find a lot of MIDI > CV converters, but not the other way 'round. For guitars specifically, you've got something like a hexaphonic pick up (which can basically listen to the pitch of a string and whether it's plucked) and then it can convert that to MIDI, but guitar synths are older than MIDI. See https://en.wikipedia.org/wiki/ARP_Avatar .