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Thread: Teensy 4.: MQS pins - what are they, where can I read about them, are they supported?

  1. #1
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    Teensy 4.: MQS pins - what are they, where can I read about them, are they supported?

    I'm researching how best to get around having no DAC on Teensy 4.0.
    I heard that something called an MQS pin can be used to substitute. I did a quick lap about looking for what MQS is and it appears to be mastering quality sound. I have little data beyond that and need to know where to look. Any help? This seems like a new feature so its plausible its not supported well on Teensy. Any data there?

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    Senior Member+ MichaelMeissner's Avatar
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    Here is a simple program that I wrote to use MQS using the Audio library.


    If you look at the Teensy 4.0 datasheet that PJRC provides, the documentation for MQS is on pages 2113-2116:

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Currently there is no software support for MQS.

    Like all the chip's peripherals, you can find details in the reference manual.

    https://www.pjrc.com/teensy/datasheets.html

    MQS is documented in chapter 38, starting on page 2113. There isn't a lot of info, but if you google for "sigma delta noise shaping" you'll find lots of info about how the underlying tech works.

    Also check out figure 36-1 on page 2066. MQS is connected to the output of SAI3, so if you're going to try writing the low-level code, you'd probably start with copying the output_i2s.cpp code for SAI1.

    Looks like MQS is actually configured by the IOMUXC_GPR_GPR2 register, documented on page 327-329.

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    I checked on the delta sigma stuff. It seems that MQS is this just a DAC that uses a different methodology, but achieves that same outcome. Am I missing something?

  5. #5
    Senior Member PaulStoffregen's Avatar
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    It's more like PWM than a true analog DAC.

    Even if you build an excellent low-pass filter, you can expect low PSRR because the high and low levels are defined by the digital power rail and ground.

    In terms of analog signal quality, it's still a far cry from a true analog DAC with a clean analog reference.

  6. #6
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    Currently there is no software support for MQS.
    Perhaps there is no advanced support for MQS, but I have been playing small Halloween WAV files that I converted via WAV2SKETCH and downloaded in memory with it this morning, connecting it to an Adafruit amplifier and a small speaker.

    Sure, using I2S instead of MQS sounds better, and when the Teensy/Amp/Speaker is near other electrical gear, I got some clicking, etc. But I thought playing mono files using MQS sounded a bit better than my 3.5 playing through DAC0 using the same speaker and amplifier. Looking at the GIT commit log, it looks like FrankB committed the changes in February.

    For my main use for having sounds as a prop, it works fine. Given that I now have the I2S boards, I am likely to use them over MQS.

  7. #7
    I am a beginner, and I feel I might have made a mistake getting the Teensy 4.0 immediately because I am lost in the mix. I thought the chip would have a DAC which I also just learned about anyway. I think I already mentioned I joined the forum and bought the teensy 4.0 because I wanted to make an analog/Digital hybrid synthesizer. So please I have a couple of questions on the digital side because I have figured some of the analog systems so far.
    My questions are:

    First, what true analog DAC would you recommend is best to use with a Teensy 4.0 and an analog synth circuit

    Second, please I am trying to have control of the analog synth through the teensy, however, I still do not fully understand the whole keyboard scanning system and midi to CV conversion business yet. I don't intend to use a "True scanned keyboard" I will just opt to use a midi keyboard such as the Arturia. So my question is if I am to design a circuit and I want to connect the Arturia from its USB to the analog circuit as a CV source for the modules, do I use the Teensy to build the control system or do I have to design a din pin for the analog circuit. Thank you and sorry for the long winded question, I just feel overwhelmed and defeated for choosing the 4.0 and not checking the earlioer versions first.

  8. #8
    I am a beginner, and I feel I might have made a mistake getting the Teensy 4.0 immediately because I am lost in the mix. I thought the chip would have a DAC which I also just learned about anyway. I think I already mentioned I joined the forum and bought the teensy 4.0 because I wanted to make an analog/Digital hybrid synthesizer. So please I have a couple of questions on the digital side because I have figured some of the analog systems so far.
    My questions are:

    First, what true analog DAC would you recommend is best to use with a Teensy 4.0 and an analog synth circuit

    Second, please I am trying to have control of the analog synth through the teensy, however, I still do not fully understand the whole keyboard scanning system and midi to CV conversion business yet. I don't intend to use a "True scanned keyboard" I will just opt to use a midi keyboard such as the Arturia. So my question is if I am to design a circuit and I want to connect the Arturia from its USB to the analog circuit as a CV source for the modules, do I use the Teensy to build the control system or do I have to design a din pin for the analog circuit. Thank you and sorry for the long winded question, I just feel overwhelmed and defeated for choosing the 4.0 and not checking the earlioer versions first.

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