What would be involved in...

[swinginguitar]

...making a detune circuit? Basically be able to tune up or down by a few cents - more or less a vibrato circuit without an LFO?

What about adding a pre-delay?

Are there any sample circuits out there for study?

In short, it would be an analog rendition of the Boss PS-5's detune mode.

[MikeH]

That's a digital trick.  If you want an analog solution, look to the knobs on you guitar's headstock 

[swinginguitar]

That's a digital trick.  If you want an analog solution, look to the knobs on you guitar's headstock 

Really? You couldn't do like a vibrato without LFO? (I'm admittedly dumb here - don't really uderstand how pitch modulation works in the analog circuit domain)

[CynicalMan]

Vibrato works by modulating the amount of delay in a delay line. For example, a signal is delayed by 5ms. If you reduce the amount of delay gradually to 1ms, then the signal stored in the delay has to go out faster and faster, squishing the signal in time and increasing the frequency. Then, you gradually increase the delay time, stretching out the signal and lowering the frequency. So to have a constant detune downwards, you'd have to continually increase the delay time, and it would become unplayable quickly. To have a constant detune upwards, you'd have to continually decrease the delay time, and you'd quickly reach no delay at all.

To make a constant pitch up, you have to guess at what some of the wave would look like and fill it in. To make a constant pitch down, you have to eliminate parts of the wave without affecting the sound too much. This is too complicated to do reasonably well with analog circuitry, which is why pitch shifters are almost all digital.

[MarcoMike]

you could play with your amp on a truck, moving at a constant speed away from where your're playing. this way your sound will be doppler-detuned.
of course then you also need a variable gain circuit to compensate for power factors... (and a long cable)

[swinginguitar]

*sigh* ...so much to learn!

Thanks everyone!

In a nutshell, how does a delay time pot actually change the delay time? Resistance controlling how long a cap stays charged?


edit: what if you had a vibrato with the rate so fast it was practically inaudible thus approaching a detuner?

[Mark Hammer]

There is such a thing as frequency shifting in the analog domain, but it is quite complicated.

Here is and example, with some soundfiles:  http://www.modcan.com/modhtml/freqshift.html

[CynicalMan]

*sigh* ...so much to learn!

Thanks everyone!

In a nutshell, how does a delay time pot actually change the delay time? Resistance controlling how long a cap stays charged?

In analog delays it usually controls the voltage on a transistor, whose resistance controls the clock speed for the delay.

edit: what if you had a vibrato with the rate so fast it was practically inaudible thus approaching a detuner?

That would sound like a ring modulator. But the average pitch shift would always have to be zero. If it wasn't, one of the two scenarios I described above would occur.

Believe me, it is tricky. You can't escape the fact that you have to construct new waves if you are shifting up, and you have to get rid of some if you are shifting down.