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Thread: Teensy 4.1 Granular Sampler

  1. #1
    Junior Member
    Join Date
    Dec 2016

    Teensy 4.1 Granular Sampler

    Got some questions a the end, concept and design first. Welcome any feedback.


    Concept isn't anything particularly unique. There are several things out there in synth land that do similar, my concept just does a few things in a way I would like more. A lot of granular samplers us the Pi and rely on pure data or Csound patches. It would be nice to have something with less power requirement and bulk. The 4.1 seems like it will have the grunt to get the job done.

    Playback with independent speed and pitch. Scanning is cyclical, won't reset on the end of a sample, only resets when set length is completed. The playback 'orbits' the sample. The clock input clocks the grains, something I would like especially when the density is very low to get a clocked delay effect. Inbuilt pitch quantize to make using it as a voice easy. Attenuverters (implemented as attenurandomizers) on all the control voltages! I lay out my concept of operations and interface notes here, Gets into details about how controls will effect behavior, alternate functions or settings, LED status display, pin assignments, etc. I could write more of that out here, but its 16 pages.

    For people familiar with eurorack I currently have a Nebulae II, Beads, and Versio that do granular in their own way, this would be more Nebulae than anything else.

    Hardware Details

    I think I have done everything right electrically, if anything stands out let me know. See the schematic attached, Orbiculatus_IO.pdf

    • MCU: Teensy 4.1, I had previously designed something for the 4.0, but the amount of expanders required to get to my feature set put me off the build.
    • Codec: CS4270, choose this because my previous choice WM8731 is OOP and seems to have I2S issues with teensy especially on MCLK. The CS4272 library is out there, didn't go for this because it is differential and single ended should be adequate for my application. If not I am open to revising to the CS4272. Inputs and outputs are appropriately scaled and buffered with opamps, OPA1678 or equivalent. I have it scaling to 3.3V, may change to 5V as the CS4270 is tolerant.
    • Controls: 3 pushbutton encoders unindexed, 4 main potentiometers, 7 trimmer potentiometers, 5 gate pushbuttons, 4 setting pushbuttons.
    • IO Expansion: 4051, 4 of these to poll the buttons, gates, and potentiometers. These should be fine without a direct I/O pin read based on what has been done for other synths.
    • Input/Output: TRS jacks, left right audio in and out. 7 control voltage inputs, 5 gate inputs.
    • SD Card: Vertical connector to get through the panel, flying wire to an adapter in the teensy.
    • LEDS: WS2812B 3535, 31 of them, had to size down to the 3535 package from 5050 to get the ring LEDs comfortably fit. Logic level shift with SN74AHC1G125.
    • Power: Will have a euro rack spec power supply for +/-12V and 5V, 3.3V for analog from LM1117-3.3, -10V reference to scale control voltages by LM4040DBZ-10, and 3.3V digital from the teesny's output.

    1. Anything about the concept beyond the capabilities of the teensy 4.1? I know there will be limitations on sample length and grain density, but will it be more than that?
    2. What is missing from the audio libraries to get these functions? I already know some things are missing, or will have to be stitched together from other libraries to get what I want. Just want to know what other people see as current shortcomings.
    3. Anything I am overlooking from the hardware side? This is an area where I am more confident in my design, I have designed and built a few analog synths, but digital design is new for me.
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