1
\$\begingroup\$

I want to make a device, which takes an AC audio signal like a guitar pickup signal, or piano or what have you as input, and changes the pitch using this function:

newFrequency = oldFrequency * 2 ^ ( ( interval - 1 ) / 12 )

oldFrequency is the frequency of current note. Interval is just the number of half-steps from that music note, including that note. For example: A note at 110Hz with interval = 13 would be A at 220Hz. A note at 110Hz with interval = 1 would be A at 110Hz. A note at 110Hz with interval = 7 would be E at 164.814Hz.

That's the case for any music note. Not only A. By the way, interval CAN take negative number for a lower pitch.

The problem is that we have an audio signal at input. One can play multiple notes or a chord at once. Is that going to be a problem?

I'm new to digital electronics, or electronics at all. I would appreciate if you could just give me keywords and leads, so that I could search, study and do more research. I don't know where to begin at all.

Thanks in advance.

\$\endgroup\$
7
  • 2
    \$\begingroup\$ "pitch shifter circuit" \$\endgroup\$ Commented Mar 17, 2015 at 15:11
  • \$\begingroup\$ I think a pitch detection technique should be researched first (I remember doing this in MATLAB a while ago, there was different approaches to this.. The best one was autocorrelation based. But it was really long time..). \$\endgroup\$
    – Eugene Sh.
    Commented Mar 17, 2015 at 15:21
  • \$\begingroup\$ @ignacio-vazquez-abrams Tried that already. I wanna learn how stuff work, and not just build something. Learning is really important to me. \$\endgroup\$
    – vahidseo
    Commented Mar 17, 2015 at 15:23
  • \$\begingroup\$ "I don't know where to begin at all" ..... "Tried that already" .... not sure I understand. You asked for keywords and leads and @Ignacio gave you some. What is it you're asking? \$\endgroup\$ Commented Mar 17, 2015 at 15:50
  • \$\begingroup\$ "learn how stuff work, and not just build something" - designing and building your own thing (rather than following a guide) is the best way to learn things! \$\endgroup\$
    – pjc50
    Commented Mar 17, 2015 at 16:25

2 Answers 2

1
\$\begingroup\$

http://www.guitarpitchshifter.com/pitchshifting.html actually explains it all quite well, but with a big emphasis on the maths. You would first need to understand the Fast Fourier Transform. From there you could implement it in software, and then start thinking about building a DSP-based device to be the actual pedal. It's within the reach of an ambitious final year project for an EE undergraduate.

\$\endgroup\$
1
  • \$\begingroup\$ Actually, I found it myself yesterday, but yeah, that's what I'm looking for. Thanks. \$\endgroup\$
    – vahidseo
    Commented Mar 18, 2015 at 18:52
1
\$\begingroup\$

I think the best you could hope for is a vocoder: -

enter image description here

Input (modulation) is voice or guitar or generally any audio. The vocoder works by filtering the input into various frequency bands, converting those band-limited signals to amplitudes and using those amplitudes to control several voltage controlled amplifiers.

The input to each VCA comes from a band-limited filter that is fed from another analogue input source called the "carrier". The carrier is usually another musical instrument such as a keyboard synthesizer.

The output is the sum of all the band limited filters that have been individually modulated by band-limited versions of the modulation signal. Vocals can be made to sound robotic or very choral/chordal and incrementing up and down in semitones is child's play.

Used em and love em!

I'm sure there are projects in google-land that are available for this to be built.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.