Optical Spring Reverb

[Knobby]

What do we reckon this is doing? Is it just a number of infrared leds and sensors either side of the springs? Presumably there's a micro controller in there as well to give the various optical modes and allow programmable selections. Could be some ideas for DIY experiments.

[DrAlx]

Interesting. It's unlikely to be measuring optical phase (i.e. no interferometry) which would mean its measuring optical amplitude.
My guess is a beam is focused on to a tiny bit of the spring (so beamwidth is less than the width of the spring wire) and measuring what is reflected back to a sensor at some nearby point.  That would be messy to set up  though (lenses, etc).
Maybe they have  a wider non-focused beam that tries to shine across the spring (at right angles to the spring direction) and with sensor placed close to the spring wire on the other side to measure how much light gets through. So that would be measuring the amount of metal obstructing the light path.  Still would be messy to set up. Too big a sensor area and the proportion of metal obstructing the light path hardly changes as the spring vibrates.  Too small a sensor area, and you could get nothing out of the sensor if it is in permanent shadow.

[amptramp]

Soloman was right.  There is nothing new under the sun.  Philco had an optical phonograph cartridge in the 1941 and 1942 model years that worked on a similar principle:

https://presto.arcade-museum.com/PRESTO-1941-2299/PRESTO-1941-2299-24.pdf

There are a number of youtube demos of this device.

It would be easy to have a differential pickup where a beam of light would shine on two photocells that were connected antiparallel so you get a positive voltage when the spring turns one way and a negative voltage when it turns the other way.  If you feed this into a transresistance amplifier (the inverting input of an op amp with a feedback resistor but no input resistor and the non-inverting input grounded), then the output is linear.

This solves the problem of how to get the signal out of a torsion spring delay line.  Rather than high-impedance pickups, just add a mirror to the end of the spring.  The difference here is that since no power is being delivered to the pickup from the spring, it may act underdamped until the reflected wave reaches the input transducer, just like an open transmission line.  Damping could be added, but as one wise marketing person once told me, "If you can't fix it, feature it."  (This wise person had a PhD in physics and an MBA.)

[iainpunk]

reminds me of optical guitar pickups!

cheers

[jatalahd]

I might be completely wrong but I see two led+phototransistor pairs, one at the top end and one just below the middle point of the springs. I am guessing that the light beam area covers maybe about five turns of the spring. The steady state bias is set so that about 50 percent of light gets through the spring wire to the transistor. As the spring compresses due to longitudinal pulses, less light reaches the transistor and when extending, more light reaches the transistor.

This creates a replica of the signal amplitude at the point of measurement.

[iainpunk]

As the spring compresses due to longitudinal pulses, less light reaches the transistor and when extending, more light reaches the transistor.

but verb springs generally move sideways or rotationally, only sketchy diy builds have them moving longitudinal... right?

cheers

[jatalahd]

If you rotate the spring, it either compresses or expands, creating longitudinal wave motion. I have not heard of transverse wave motion being utilized in spring reverbs.

[garcho]

Here's my question: y tho?

Does this do something different sonically? Game Changer seems to make stuff that looks really cool and sophisticated but sounds dime-a-dozen.

[iainpunk]

If you rotate the spring, it either compresses or expands, creating longitudinal wave motion.

that sounds really logical, i feel dumb now

I have not heard of transverse wave motion being utilized in spring reverbs.

the reverb i build with a friend of mine had a tank with actuators moving the spring sideways, it was a really bass-heavy reverb tank, and we had a high amount of bass cut before going in to the spring tank.

Here's my question: y tho?

Does this do something different sonically? Game Changer seems to make stuff that looks really cool and sophisticated but sounds dime-a-dozen.

i have the same feelings towards gamechanger, although i like the ''more'' pedal, but its essentially an EHX Freeze, with less artefacting and glitches.
that ''plasma'' pedal sounds like a gated FF and kinda falls away in a life mix. their 'more' is basically an EHX Freeze, and this is just a gimmicky reverb. their products are a bit like the 3 latest starwars movies, a lot of hype, a lot of cost, but the same-old same-old as most sci-fi these days.

cheers

[Rob Strand]

i build with a friend of mine had a tank with actuators moving the spring sideways, it was a really bass-heavy reverb tank, and we had a high amount of bass cut before going in to the spring tank.

Having gone through a lot of details of this a few years back there is a reason for the rotary idea.   The reason relates to the sensing end.   A rotary sensor is less susceptible to detecting horizontal and vertical movements of the spring.  That reduces mechanical noise and feedback due to acoustic coupling of the sound from the speaker back through the speaker enclosure and then to the spring.

The transverse drive works.   It's just that the reverb spring designers try to reduce the vibration issues with slightly more "clever" motor design.   If you knock out the vibration by even 6dB that would save a lot of headaches.

Does this do something different sonically? Game Changer seems to make stuff that looks really cool and sophisticated but sounds dime-a-dozen.

I can ear artifacts in the reverb signal as if the detection isn't done right.

[Knobby]

Found another video last night where the designer discusses how it works:

[merlinb]

It's looks super cool, but I'm logging it under 'solutions in search of problems'.

[Frank_NH]

Interesting but after listening to the demo I would say at least 90% of the sounds would be unusable for me.  FV1-based pedals are cheaper and can do largely the same kind of thing.

[Digital Larry]

I can ear artifacts in the reverb signal as if the detection isn't done right.

You say that as though it's a bad thing.   

I'll give these guys points for "thinking outside the box"... sort of like my cat does occasionally.  The flashing lights/eye candy are part of the "optical effect".  Maybe this thing wants a mic stand mount so the audience can see it better.

That said, on some other gear forum there were a number of posts anticipating the release, and not so many in the aftermath raving about it.

[Rob Strand]

You say that as though it's a bad thing.   

I guess the way to phrase it is, would you replace your magnetic pickups with optical pickups with those artifacts present.

These guys have got some good ideas,
https://patentimages.storage.googleapis.com/d6/24/b2/113831c19dbd19/US5237126.pdf

You can listen to sound samples on youtube.   As far as emulating and replacing magnetic pickup, there's still room to move.   Not such an issue for a reverb but the magnets in guitar pickups remove the need for a power source.   The optical systems need power to power the light source.

Good history of ideas in the references,
https://www.researchgate.net/profile/Ibrahim-Kubilay-2/publication/327750725_Optical_Pickups_for_String_Musical_Instruments/links/5ba2445c299bf13e603c89fa/Optical-Pickups-for-String-Musical-Instruments.pdf?origin=publication_detail