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Lower the Pitch in real time

  1. Sep 11, 2014 #1
    I want to project a circuit that lower the pitch of a sound input by half and plays it closer to real time as possible. I thought about converting the input to digital and then to analogical, with a slower clock. But I wonder if i could do it using only analogical electronics.
  2. jcsd
  3. Sep 11, 2014 #2
    I don't think the term "real time" is applicable here. If the beginning of your converted sound coincides with the beginning of the original sound, then the end of the converted sound will occur at double the length of the original.
  4. Sep 11, 2014 #3


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    There are many guitar effects pedals that do this; to make the guitar sound like a bass by lowering the pitch an octave.

    Read about them on wiki:

    Most pedal schematics can be found online via google.

    All of the analog ones are monophonic And (like all effects pedals) there is no noticeable time delay, no one would buy a pedal that puts you behind the beat!

    Check out the EHX POG, HOG and POG 2 for polyphonic circuits. (P/HOG = polyphonic/Harmonic octave generator).
  5. Sep 11, 2014 #4


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    Software to process audio to change the pitch and the speed of music independently by arbitrary amounts (not just factors of 2) is easy to find. Of course it introduces some form of distortion, either by cutting out cycles of the original or repeating them, but the results are acceptable to listen to, whatever a frequency analyzer or distortion meter might say about them. The signal processing algorithms are well known.

    The speed of sound in air is about 1 foot per millisecond, so "real time" processing delays of a few milliseconds are not very important, and a modern PC can do a lot of processing in a few milliseconds.
  6. Sep 12, 2014 #5

    jim hardy

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    Try a search on "Darth Vader Voice" .
  7. Sep 12, 2014 #6


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    If you are providing a continuous output from a processor - rather than batch processing - you can call it 'real time'. If you want to be fussy you would say that absolutely any electronic processing introduces some delay and it's not really real time.

    The original 'real time' pitch changing was done with a tape with a fixed record head and a set of playback heads on a rotating drum (like on a VHS player). The heads would read off the tape faster or slower than the recorded material - according to which way the drum was rotating. Of course, each replay head would rotate until it lost contact with the tape and then another head would take over. Fine - except there was a change of phase and amplitude as one head took over from another. It's not hard to do the equivalent with a RAM based system. You can get a much more convincing effect this way because you can window the data as you crossover between 'virtual' read heads (memory pointers).
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