Why do vactrols sound the way they do?

[andrewl0]

I understand that vactrols are optocouplers and their usage in traditional circuit design. What I don't understand is why they generate a "rubbery" sound in audio circuits.

Does anyone have any pointers to articles that explain how putting an optocoupler in an audio circuit generates the timbres that I associate with Make Noise modules?

Many thanks!

[bleeps]

Vactrols are a pairing of an LED and a photo-sensitive cell. LEDs don't shut off immediately when you cut the power to them. They fade. That trailing, delayed fade is what gives them their character.

Also they have unicorn tears inside.

[Mono Recalcitrante]

Also they have unicorn tears inside.

[Ucture]

Vactrols explained by Scott Stites :
http://experimentalistsanonymous.com/bo ... pic=1254.0

[andrewl0]

Thanks folks, now that I know about the unicorn tears everything makes sense!

[ultrashock]

the main point that vactrols have non-linear response.
human's perception as well as most physical and chemical processes in human organism are also non-linear. far not. that why vactrol's character fits so 'natural' to what we feel and is considered to sound 'musical' without any tricks just out or the box

[Drumdrumdrumdrum]

They have unicorns inside!

[paults]

LEDs don't shut off immediately when you cut the power to them. They fade.

Ummmmmm...no. It's the Cadmium-Sulfide photocell that turns off/on slowly. In fact, you can specify just how fast/slow by the part number. Also, by modulating the LED current, you can vary the resistance as well (with the lag factor built-in).

human's perception as well as most physical and chemical processes in human organism are also non-linear. far not. that why vactrol's character fits so 'natural' to what we feel and is considered to sound 'musical' without any tricks just out or the box

Lord.....

[daverj]

Vactrols are a pairing of an LED and a photo-sensitive cell. LEDs don't shut off immediately when you cut the power to them. They fade. That trailing, delayed fade is what gives them their character.

Also they have unicorn tears inside.

LEDs don't fade in any noticeable amount. The slowest LEDs can be turned completely on or off in a few hundred nanoseconds, while the fastest ones can do it in a tenth of a nanosecond. Most LEDs can put out a square wave of light (completely on to completely off) at well beyond a Mhz.

It's the photocell that has the long response times and slow rise and fall. It's those delayed reactions to the fast changes of light from the LED that give a Vactrol it's slow "rubbery" behavior. The response times of the type of Vactrols used in synths is measured in milliseconds. That's slow enough that we can hear the difference in rise or fall of a CV compared to one that turns on and off quickly.

Basically it is adding a delay and a non-linear slew to the signal going into it. It's possible to create the exact same effect purely electronically, without Vactrols. But it's typically cheaper to just use a Vactrol. And a lot simpler in some applications. Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound. (but it's not)

[Just me]

And I always thought there was kitten breath inside.

[Tim Stinchcombe]

Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound.

And no one has even mentioned ringing yet...

[dkcg]

And I always thought there was kitten breath inside.

I thought it was fairy farts. :(

[Ebolatone]

Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound.

And no one has even mentioned ringing yet...

Please do!

[MR-808]

Hysteresis.

[Yohda]

Basically it is adding a delay and a non-linear slew to the signal going into it. It's possible to create the exact same effect purely electronically, without Vactrols. But it's typically cheaper to just use a Vactrol. And a lot simpler in some applications. Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound. (but it's not)

Are you only talking about the way vactrols react to modulation or about the sound too ?

Ime, vactrols filters have a sound i have never heard reproduced. Very soft and smooth.

[Jason Brock]

Hysteresis.

There's a home remedy for that now, in case you didn't know.
I bet it has vactrols in it somewhere.

[krz]

2nd level harmonics are pleasing to the human ear. 3rd level harmonics from vactrols/tubes are the next most pleasing harmonics ...iirc.

[falafelbiels]

[darenager]

^ He don't look pleased, I suspect a faulty vactrol or counterfeit part.

[darenager]

Oh yeah ringing, well vactrols love to be rang, simply look at the part number on the side and call them from your telephone (tip, analog phones work best) they are always really happy to speak, so don't feel shy.

[Drumdrumdrumdrum]

simply look at the part number on the side and call them from your telephone

[Tim Stinchcombe]

"I don't hear no goddamn ringing!"

[daverj]

Basically it is adding a delay and a non-linear slew to the signal going into it. It's possible to create the exact same effect purely electronically, without Vactrols. But it's typically cheaper to just use a Vactrol. And a lot simpler in some applications. Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound. (but it's not)

Are you only talking about the way vactrols react to modulation or about the sound too ?

Ime, vactrols filters have a sound i have never heard reproduced. Very soft and smooth.

Vactrol filters, like Buchla 292 and Makenoise QMMG are very simple 12db/oct Sallen-Key filters that would normally have fixed resistors and capacitors, and be set to a specific single frequency. The Vactrol allows them to be voltage controlled. A dual gang pot would allow them to be manually controlled the same way, without a Vactrol.

Because the resistance of dual Vactrols, like those used in those filters, are not very accurate, instead of getting a true 12db/oct adjustable filter it's more like two 6db/oct filters with the frequency settings not matching or tracking exactly. So the resulting slope is going to be more like 6db/oct for a little range of frequencies, and then 12db/oct above that.

[sduck]

Basically it is adding a delay and a non-linear slew to the signal going into it. It's possible to create the exact same effect purely electronically, without Vactrols. But it's typically cheaper to just use a Vactrol. And a lot simpler in some applications. Plus people have romanticized and mysticized this antique technology and feel like it's required to get that sound. (but it's not)

Are you only talking about the way vactrols react to modulation or about the sound too ?

Ime, vactrols filters have a sound i have never heard reproduced. Very soft and smooth.

Vactrol filters, like Buchla 292 and Makenoise QMMG are very simple 12db/oct Sallen-Key filters that would normally have fixed resistors and capacitors, and be set to a specific single frequency. The Vactrol allows them to be voltage controlled. A dual gang pot would allow them to be manually controlled the same way, without a Vactrol.

Because the resistance of dual Vactrols, like those used in those filters, are not very accurate, instead of getting a true 12db/oct adjustable filter it's more like two 6db/oct filters with the frequency settings not matching or tracking exactly. So the resulting slope is going to be more like 6db/oct for a little range of frequencies, and then 12db/oct above that.

In other words they actually sound like shit. We just like it that way cause we've gotten used to it.

[sduck]

I wonder what ever happened to that guy who was trolling for advice here a while back - he wanted to design his own version of a LPG, but without vactrols because he hated them. He liked everything else about LPG's, except for the fact that they had vactrols in them.