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Thread: More than one USB input?

  1. #1
    Junior Member
    Join Date
    Mar 2014

    More than one USB input?


    Can a teensy w/ audioBoards support two USB inputs?

    Attempting this:

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    Currently testing two audioBoards (with quad mods) with a teensy 3.2.

    LineIn is Sent to host, Modified with effects, Returned to interface, Mixed with system audio from host, then out to headphone jack.

    Its to get around a limitation in the host os where system audio can't be gain leveled with other material.

    I can do this with commercially available USB interfaces. System audio always appears on 1&2.

    I'm only seeing one usb interface.

    Does it support this capability?

  2. #2
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Quote Originally Posted by jmercer View Post
    Does it support this capability?
    No, sorry, the code is written for 2 channels (1 stereo) input and 2 channels output.

    But it is all open source, so in theory you could edit the code to tell your PC the input is 4 channels. You'd also need to double the IN endpoint packet size, and alter the code which receives the data to double the buffer size. The audio library interface code would also need to change to pull 4 channels from the buffer instead of only 2.

    While all this is possible in principle, the reality is the USB audio code isn't simple, and troubleshooting when anything goes wrong can be quite tough.

    Also, running 6 channels simultaneously would mean an IN endpoint size of 360 bytes and the OUT endpoint at 180 bytes. Most frames actually will have packets of 352 & 176 bytes, since 44 samples per millisecond is the norm, but occasionally 45 are needed since the sample rate is 44.117 kHz. 540 bytes in a frame is about half of the 12 Mbit/sec USB bandwidth. That should still work, but it's getting up there...

  3. #3
    Junior Member
    Join Date
    Mar 2014
    Thank you for the detailed response, Paul.

    That's way beyond my current skill level !!!


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