The "Modelers Don't Clean Up with the Volume Knob" Myth

Motor in this context means speaker motor, not an electric rotary motor.

The time of flight between the speaker and the guitar is also a big factor. This imparts a phase shift to the various frequencies. No delay, no phase shift. As you vary the distance the phase will change causing some frequencies to constructively interfere and others to destructively interfere. That's why as you move you can coax the feedback to break into a harmonic.

An electromagnetic transducer driven by the pickup output is not the same as acoustic energy from the amp being absorbed by the guitar. A big difference is you lose the nonlinearity which inherently "stabilizes" the loop. A common (old) technique used in the design of oscillators is to use a positive feedback loop with a nonlinearity. The nonlinearity reduces the loop gain which stabilizes the loop. This technique is probably all but lost to modern synthesis techniques but I digress.

When your guitar is in controlled feedback it's an oscillator. The amp distorts which causes the loop gain to drop stabilizing the loop and giving a controlled oscillation.
 
Rex said:
Not a spinning kind of motor. The loudspeaker kind. The part of the speaker that's not the cone or the basket...
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I had envisioned a small electric motor with an offset load on it so it'd "rattle" the body at a high frequency. Equivalent, no? The idea here is to inject vibrations into the body that move the pickups relative to the strings to cause motion in the magnetic field that gets set as a current down the wire to the detector.
 
FractalAudio said:
A big difference is you lose the nonlinearity which inherently "stabilizes" the loop.
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But there's no loop here if you're driving the guitar body with a motor that's not gathering data from the system, right? This is all in the context of doing things without lots of volume, no? You can't stabilize it because the motor itself isn't getting any signal from the interaction. Or maybe I missed that you'd feed the motor some signal from the Axe-Fx or something like that to close the loop?
 
“Motor” in this context means the part of the speaker that converts electrical signals into mechanical signals. Every loudspeaker has a motor. The motor is fed with the audio signal from the Axe/amp. In turn, the motor drives the speaker cone and makes it move.
 
FractalAudio said:
The time of flight between the speaker and the guitar is also a big factor. This imparts a phase shift to the various frequencies. No delay, no phase shift. As you vary the distance the phase will change causing some frequencies to constructively interfere and others to destructively interfere. That's why as you move you can coax the feedback to break into a harmonic.
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Right on. It's something I learned how to feel. Leaning just a bit closer or further can help certain notes grab either a fundamental or a harmonic. The system's favorite pitch gets higher as you lean closer and lower as you lean away, so it makes sense there is phase shift due to (in this case) distance tweaking the loop's happy frequency. Works just like the three RC lowpass filters in a trem LFO, if you look at it sorta sideways. Distance from the speaker is the 'speed pot' that tweaks the oscillator frequency. Practice it a bit, and you can match that distance to the note you are playing and the guitar and amp just take flight. I also got good at phrasing lines that sounded backmasked, in combination with the feedback, to play 'backwards' lines in live performance. Got more than a few 'Nipper Dog' looks from people in the crowd with that.... :D I miss the '90s....
 
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The one problem I see, based on the description of the planned device, is the lack of ability to tune the delay to coax certain notes to fly. If it clamps on the guitar, you can't lean closer or further to tune the delay to the note you want. Try as you might, you can't lean just so and catch that 9th in the outro of White Room if it's clamped on and a fixed delay is setting the 'distance'....
 
Joe Bfstplk said:
The one problem I see, based on the description of the planned device, is the lack of ability to tune the delay to coax certain notes to fly. If it clamps on the guitar, you can't lean closer or further to tune the delay to the note you want. Try as you might, you can't lean just so and catch that 9th in the outro of White Room if it's clamped on and a fixed delay is setting the 'distance'....
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I wonder if the delay "distance" could be controlled by an expression pedal?
 
FractalAudio said:
It can't be self-contained. The signal to the motor needs to come from the output of the amplifier and should ideally be delayed a bit. Also, there needs to be EQ to simulate the absorption coefficient. Clamping a motor to the body causes nearly unity absorption whereas in air the body is going to absorb different frequencies more.
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Maybe self contained was the wrong terminology. I was imagining something that was attached to the guitar, whether hardwired or not but didn't need any cables running along the ground. I built a very simple amp and fuzz circuit that fit in the control cavity, then running to different sized transducers attached to the body (testing different sizes and placement). I wired in a second input jack for simplicity. I like EMG's design of running 9-18v through a TRS cable so maybe this small amp could be powered this way? I'm FAR from an electrical engineer so excuse me if I come off ignorant, but I enjoy tinkering.
 
iaresee said:
But there's no loop here if you're driving the guitar body with a motor that's not gathering data from the system, right? This is all in the context of doing things without lots of volume, no? You can't stabilize it because the motor itself isn't getting any signal from the interaction. Or maybe I missed that you'd feed the motor some signal from the Axe-Fx or something like that to close the loop?
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Here:​
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FractalAudio said:
It can't be self-contained. The signal to the motor needs to come from the output of the amplifier and should ideally be delayed a bit. Also, there needs to be EQ to simulate the absorption coefficient. Clamping a motor to the body causes nearly unity absorption whereas in air the body is going to absorb different frequencies more.​
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Joe Bfstplk said:
The one problem I see, based on the description of the planned device, is the lack of ability to tune the delay to coax certain notes to fly. If it clamps on the guitar, you can't lean closer or further to tune the delay to the note you want. Try as you might, you can't lean just so and catch that 9th in the outro of White Room if it's clamped on and a fixed delay is setting the 'distance'....
Click to expand...
SalazarMcMantis said:
I wonder if the delay "distance" could be controlled by an expression pedal?
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Incorporate a gyroscope? lol
 
Rex said:
The Axe-Fx offers many ways to control delay with an expression pedal.
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Absolutely, I was meaning in this case to simulate the distance from the speaker. If changing the delay time could effect the the feedback frequency, then controlling it with an expression pedal could potentially work as-if moving the guitar further or closer from the amp.
 
SalazarMcMantis said:
Absolutely, I was meaning in this case to simulate the distance from the speaker. If changing the delay time could effect the the feedback frequency, then controlling it with an expression pedal could potentially work as-if moving the guitar further or closer from the amp.
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That’s my point. If you have such a feedbacker device, you could feed it from one of the Axe’s output ports. Right before that output port, you could drop in a Delay block. Tie that delay to an expression pedal, and you’re good to go.
 
Rex said:
That’s my point. If you have such a feedbacker device, you could feed it from one of the Axe’s output ports. Right before that output port, you could drop in a Delay block. Tie that delay to an expression pedal, and you’re good to go.
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Gotcha, so we're saying the same thing. I'm going to give it a try in a bit.
 
SalazarMcMantis said:
Gotcha, so we're saying the same thing. I'm going to give it a try in a bit.
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+1.

One thing to watch out for: when you vary a delay on the fly, you get a momentary pitch-shifting artifact. You'll want to keep those changes small enough and slow enough that those artifacts are too small to be noticed. The maximum sweep should only be a few milliseconds. The delay in the Cab block is small and very granular. I'm not near my Axe, and I don't recall whether guit can tie a modifier to that.
 
I kind of understood this growing up playing loud , messing around with feedback of amps etc.... so I have to ask you this one Cliff, does the magnetic field of the speaker change and probably reacting with the guitar at high volumes? and if so , can it be simulated ? it would explain why you have to stand on stage in certain areas to get the feedback to higher octaves to me, but is it possible to simulate it ( or replicate that reaction )
at lower volumes .... just curious where your going with this .... thanks !

not to be off topic btw, but I just realized you have done something in you sould be very proud of...
you have brought the crown back to the usa so to speak on top notch effects processing , instead
of being made overseas from some other country ....... I am very excited about the future of modeling !
 
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