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Thread: Sequencer drum machine SAMPLE (remake korg sample)

  1. #1
    Junior Member
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    Sequencer drum machine SAMPLE (remake korg sample)

    Hello, i write from italy (sorry for my english).
    I want to make a sequencer / sampler similar to KORG SAMPLE with teensy + audio board sgtl.
    In the audio library is not included the part of being able to change the tone of a wav file, are there any updates?
    Is it possible to remake the korg with teensy?
    do you have ideas, suggestions, projects on the internet etc. to post?

    Click image for larger version. 

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  2. #2
    Senior Member+ Theremingenieur's Avatar
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    Easiest would be to simply change the sampling rate which corresponds to running an analog tape quicker or slower. But the sampling rate has to remain constant at 44.1kS/s, so you'd have to oversample the original signal by interpolation with filtering and then to pick just the samples which fit into the corresponding desired pitch scheme.
    That's very complex mathematics which is a bit heavy for a Teensy, especially if you want to have it in real time, and that's why I think nobody has done it yet besides of simple octave transposition which consists in either dropping each second sample or interpolating just one sample between two existing ones.
    There are open source pitch changing algorithms out there in the wild, audio software like audacity does for example use one, but you would have to port it to the Teensy.

    A less perfect workaround would be writing code which outputs the wav file at variable sample rate through an external SPI DAC without using the audio library, going through an analog reconstruction filter and resampling that analog signal which has then already the modified pitch using the internal ADC at the fixed sampling rate with the audio library.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Last year a group of students (who I advised) did a project to add this sort of sample-based (or "wavetable") synthesis.

    https://github.com/TeensyAudio/Wavetable-Synthesis

    Recently I've been merging this into the Audio library. It's in the latest beta and will be in the 1.44 version (later this week).

  4. #4
    Senior Member
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    Nov 2015
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    Thanks Paul, this is a great news!
    with a couple of friends we are working on a drum-machine kit THC with teensy 3.6, the audio output is on the DAC of 3.6 we do not use the audio board to make the kit cost less.

    Some kits should be on sale at the next Soundmit (www.soundmit.com), initially we will make 5/10.
    We invite everyone to change the firmware that will be available on our site in a few weeks!

    This is the prototype with some smd components, next prototype will be different
    if you have request, write here, we try to add them
    one of the thing will be a small breadboard on the right

    Click image for larger version. 

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