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Thread: How many inputs can be processed?

  1. #1

    How many inputs can be processed?

    The audio shield has five mono inputs (2 ◊ stereo + 1 ◊ mic), and then the Teensy 3.6 has 2 ADCs.

    Using AudioControlSGTL5000::inputSelect(), however, it only seems to be possible to select one stereo input, i.e. two mono inputs.

    Is it possible to work with more than two mono inputs?

  2. #2
    Senior Member+ Frank B's Avatar
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    With a single SGTL5000 shield: No.

  3. #3
    Quote Originally Posted by Frank B View Post
    With a single SGTL5000 shield: No.
    According to my own research, it should be possible to use the two ADCs as well. That would give a total of four inputs. I haven't tried it yet.

    However, I would want to keep one ADC for reading potiometers. So that would mean no more than three inputs, unless I get an extra shield.

  4. #4
    Senior Member+ Frank B's Avatar
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    Of course you can use more, but the shield provides only two.
    Paul added 8channel I2S recently, for example.
    You did'nt even say for which Teensy you're asking. For Teensy 4 for example, ADC - Audio is WIP.
    Then, SD can be seen as an input, too.

  5. #5
    Senior Member+ Frank B's Avatar
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    You can't use the two ADCs for audio AND other inputs.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    If you use Teensy 4.0, and if you get the latest audio library code from github (or wait a few days and get 1.52 beta which will have it), and if you're able to work from help here and comments in the code (but not yet nice documentation written on the website or design tool) then you could connect 3 audio shields. You could even connect 4 or 5 of them for 8 or 10 channel input, if you don't need all of them to have working outputs.

    Connecting more than 2 audio shields (Teensy 4 only) also requires special with for the I2C communication to control them. Only 2 can connect to the same I2C bus (SDA & SCL pins) to configuration setup, because the SGTL5000 has only a single I2C address pin. The audio library's code to configure the hardware assumes they're connected to the main I2C pins (18 & 19). You'll need to copy & modify that code to configure the 3rd audio shield.

    On Teensy 4.0, the built-in ADC pins are not yet supported for audio input. They can only be used for pots. They do work for (lower quality) audio on Teensy 3.x, but using the ADC pins for audio means the ADC is always busy for audio signals and can't be used for reading pots.

    With either Teensy 3 or 4, you could use TDM instead of I2S, and connect a CS42448 chip which gives 6 inputs. TDM support many more channels than I2S.

    https://oshpark.com/shared_projects/2Yj6rFaW

    (click the "Description" button on that page to see all the info)

    This might be the best solution for you. The only download is currently nobody sells a CS42448 shield. It's available only as a DIY soldering project.

    On Teensy 4.0, it's even possible to connect two TDM chips...

  7. #7
    Quote Originally Posted by Frank B View Post
    You did'nt even say for which Teensy you're asking.
    See my original post: 3.6

    Quote Originally Posted by PaulStoffregen View Post
    If you use Teensy 4.0
    A Teensy 3.6 plus matching audio shield was easier to get. Iím in Hong Kong, ordered from Taobao. Itís more expensive here than in the West. I shouldíve ordered two audio shields though. Then we could do four channels.

    But for now, weíll simply be using an external mixer in addition. I would love to eventually try the Teensy 4.0 with three shields. Also the TDM suggestion is interesting.

    Anyhow, thanks for the detailed reply! Itís a bit overwhelming, and Iím at the moment struggling with more basic problems, including noise and hum. It is the first time that Iím using the Teensy with audio, and indeed it is great fun. We want to do sound recordings in the jungle, maybe hook up some measurements, such as change of resistance as a plant grows, to filters.

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