Tremolo effect idea - already been done?

[Mark Lavelle]

Back in 2003 I was briefly obsessed with an idea for a ridiculously flexible tremolo effect that would allow the LFO wave shape to be almost anything you wanted, and I'm now I'm thinking about actually building it. While it would obviously be applicable to guitar, I think there are other musical uses.

To get beyond triangle, square, sine & pulse shapes I'll generate the LFO wave shape with a microcontroller. I want to control each phase individually, a la ADSR envelopes: shape1; hold1; shape2; hold2. In addition, each of the shape phases could be any straight line slope or any 1/4 sine wave slope (speed, really), parabola or other interesting 2D curves. I'm even going to play with drawing the LFO forms. I also have ideas for a few different depth control modes.

There are all kinds of things to resolve, and right now I'm thinking about the 'user interface.' Are there super-flexible Tremolo or LFO units already out there that I should look at? Am I insane?

[Enzo]

I hope it is a fun experiment. Thinking about it in my head though, I suspect you are over-estimating the LFO waveform's ability to be heard. To my mind there is very little difference between sine and triangle wave in an LFO. Square wave? Sure, it makes the sound on/off.

Two of my favorite albums are Jeff Beck's Wired and BLow By Blow. The two records sound similar and were my go-to LPs for turntable testing. BUT... the electric piano on them was hard panned left and right and the trem was like a switch. The piano sound ping ponged left and right all the time. Not a smooth slide left to right and back, but a hard switch. Listen to either channel alone and the piano turned off and on a couple times a second. VERY annoying.

I think your LFO would have to control an interface that was totally electronic. meaning no bulbs and no photocells. A bulb is not instant on or off. An LED pretty much is, but not a light bulb. SO any sharp turns on your LFO curve will be smoothed out by a bulb's inherent delay. Likewise, photocells are not instant, they take some amount of time to recover each pulse. So there again, they tend to smooth out any sudden jerks in the LFO wave.

Sine and triangle waves tend to be smooth. A sawtooth wave tends to be a little more precussive.

I could be wrong, but I think the differences between your fancy waveforms would be like switching cathode resistors on your input stage between 1400, 1500, and 1600 ohms. In other words, not a lot.;

[Mark Lavelle]

Well, the point is to experiment... ;-)

Fancy curves will surely be inaudible at typical trem rates, but I'm curious about sub-4Hz rates (where at max depth it'll effectively be a repeating ADSR). While guitar toys are always fun, part of my rekindled interest is that I think this could be a useful electronic/musique concrete tool.

I hadn't decided about stereo ping-ponging, but I'll probably save that for the deluxe edition.

The basic concept is that a processor digitally sets the gain on an op-amp, so I'm going to be prototyping on the STM32F303. The EVAL board has way more features than I'll ever use, but I wanted the display...

[Enzo]

You could certainly connect a function generator in place of the existing LFO in some conventional trem circuit. That would let you quickly select sine, triangle, sawtooth, or square, as well as duty cycle. Play with that as a proof of concept.

[Randall]

"Two of my favorite albums are Jeff Beck's Wired and BLow By Blow."

I knew I liked you!

[Mark Lavelle]

You could certainly connect a function generator in place of the existing LFO in some conventional trem circuit. That would let you quickly select sine, triangle, sawtooth, or square, as well as duty cycle. Play with that as a proof of concept.

Yeah, I'm basically doing exactly that, except I don't have a function generator so the first step is building my own!

A big attraction of this project is getting back into microcontroller programming, which I haven't done for my job or myself for several years now. So for I've been able to find free dev tools (Atollic IDE, compiler, etc) and plenty of sample code, so the only cost has been the HW. As of yesterday I can modify, compile & debug the eval board demo app, so the real fun is just starting.

[Tone Meister]

... Two of my favorite albums are Jeff Beck's Wired and BLow By Blow...

"Two of my favorite albums are Jeff Beck's Wired and BLow By Blow."

I knew I liked you!

... and Guitar Shop and Who Else!

[uneumann]

Yeah, I'm basically doing exactly that, except I don't have a function generator so the first step is building my own!

A big attraction of this project is getting back into microcontroller programming, which I haven't done for my job or myself for several years now. So for I've been able to find free dev tools (Atollic IDE, compiler, etc) and plenty of sample code, so the only cost has been the HW. As of yesterday I can modify, compile & debug the eval board demo app, so the real fun is just starting.

Sounds like a fun project that could keep going for a while.

You can poke around on the web to see what's already out there. Here are a two that seem relevant to your direction.
They may be a good source of inspiration - or at least some good marketing lingo...

Delta-Trem Tube Tremolo | Effectrode "... authentically recreates the alluring, hypnotic tone and feel of a vintage amp tremolo. This is accomplished by using a ‘Raysistor’, ... "

EHX.com | Super Pulsar - Stereo Tap Tremolo | Electro-Harmonix "Sculpt the tremolo’s shape with adjustable sine, triangle and pulse waveforms while tap tempo and tap divide ensure synchronicity."

cheers

[Dave H]

I could be wrong, but I think the differences between your fancy waveforms would be like switching cathode resistors on your input stage between 1400, 1500, and 1600 ohms. In other words, not a lot.;

I don't think you're wrong. I've tried it with a function generator and it wasn't worth doing.

[Mick Bailey]

The changes need to be pretty dramatic to get a noticeable effect - our hearing isn't particularly sensitive to subtle amplitude changes. My sequencer can be set up to produce a custom waveform and then the output voltage used as a control input to a VCA. Overall, there has to be a dramatic amplitude change with a high modulation depth to get any useful results. Some of the slow ramp waveforms are good, and asymmetric shapes, too. Largely though I've settled on two shapes for trem; square wave and a sawtooth waveform that can be morphed either side of a triangle. Pretty much what you can end up with a Tremulus Lune build if the supplementary waveform switch is replaced by a pot.

An interesting pseudo ring-mod effect can be had with a square wave set to 100% modulation depth and high frequency, though. Also, varying the duty-cycle of the modulation, or applying rhythmic variations in frequency have a greater effect than just simple amplitude modulation. This creates the impression of frequency variations or rhythm in the effected sound.

For me, I would build just a modulation box as you describe, and use it as a plug-in unit to control pitch or time-based effects, as trem just doesn't respond well to slight changes in waveform. I'd include duty cycle functions as well as the ability to frequency-modulate the output. If you used the output to drive a Vactrol you can then piggy-back the resistor side onto a pot (thinking here the delay time pot on a digital delay) to get interesting programmable chorus/pitch/delay effects. A PT2399 delay can be a good candidate for this type of thing.

[Mark Lavelle]

The changes need to be pretty dramatic to get a noticeable effect - our hearing isn't particularly sensitive to subtle amplitude changes.

That's especially true in traditional tremolo applications, where the changes are too fast to parse, and I don't expect any really useful differences between curves and straight lines in that mode. But I'm also looking at is as a repeating (or maybe even triggered one-shot) ADSR+, where a difference in fade in or out has more time to be heard.

I like the idea of modulating the duty cycle. I had already thought about a very limited version, but now I see it as applying an LFO the duty cycle. I'll definitely be borrowing that idea...

That's the great thing about modern MCUs -- everything's 32-bit and timers & PWMs are basically free. Even the eval boards are better, and the ST I'm using is available on a cheap module/board if you're interested in building a small batch. So the 21st century has at least some good attributes...

[Mick Bailey]

I've used my synth as an envelope shaper for guitar, both triggered off the guitar signal itself, and by using the LFO to trigger the envelope generators and then timing the guitar picking to coincide with the triggering. When using the LFO. it's useful to put that under foot control and then the 'beat' can be synchronised to a track or the rest of the band. It gives some flexibility in timing that sounds less quantized or rigid. Using slightly slower envelopes results in some pretty interesting sounds that range from organ swells to reverse-sounding effects. Another aspect of foot control is to get Tom Morello style effects with the modulation depth set to 100% and using a square wave LFO.

[eschertron]

Hooking an function generator/LFO into an amp's bias circuit sounds like a reasonable first step towards getting analog modular synthesis techniques incorporated into the guitar player's world. But what then? You'll have to try more and different things. Voltage-controlled tone stack perhaps?

I can imagine LFOs, envelope generators, VCAs and VCFs as part of a rig's preamp circuitry; I imagine also that it'd be more flexible as part of a standalone synth package, inserted at the amp input or FX loop. I have a handful of Craig Anderton's designs that I've played with in the past, and love the idea of synth guitar. At what point does the amp cease to be the 'main' sound processing device, and become one element in the signal chain? Already with post-preamp FX loops, many amps can be though of as two discrete blocks, preamp and power amp. Standalone preamps have been a thing for a few decades.

You may find that programmable LFO-controlled trem may be a neat thing, but if it works well you'll want more control. That's a path you may never return from, once begun. So beware, and happy hunting!

[Enzo]

The point of function generators was proof of concept: it shows you whether more complex trem envelopes are audible or not. It will demonstrate that building and entire system might pay off or might be a waste of time.

[Roberto]

I think you can find this interesting:
HRI ? Huge Racks Inc ? View topic - Mastering MODULATION... secrets to magic powers & finesse.

Well, I'm doing the same (a signale generator), but I want to implement AM and FM modulation too.
Then I'll transmit those five signals through midi (scaled 0-127) to continuously change the parameters of the effects in my rack.

Have you already developed the code to do that?
I'll do it on an Arduino, not a STM32, possibly with a smaller HMI.