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Thread: 24 bit audio boards

  1. #151
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    Quote Originally Posted by CyborgEars View Post
    I2S microphones are tiny SMD parts which are meant to sit somewhere on the pcb of a multimedia / audio device and, if enabled, continuously record audio samples with their internal ADC and shove the resulting data stream to a MCU or CODEC. The microphone designers decided it would be wise to use a very streamlined set of data lines and do only include I2S and NO other means of controlling any sample settings beyond the primitive ENABLE and LEFT/RIGHT pins and the sampling frequency, which is controllable via I2S clocks.

    One therefore has no control over any gain or sample depth setting of the ADC stage of an I2S microphone. This fact might have also led to - but I'm not confident about this fact - the follow-up decision by the audio designers to use fixed 24bit depth for the I2S data transfer. This is the crucial point why I've decided that cutting bits most definitely has some repercussions along the way.

    I'ld be happy if this assumption is wrong, because then things get a lot easier on all fronts

    Even after a lot of reading on this subject, I'm not exactly sure if 24 bits are really necessary, and if so, why.
    The I2S mic in question* has 91dB "digital range" between its noisefloor and +120dB SPL...
    To resurrect this old thread, I've also been checking out the I2S digital microphones. I find them very intriguing as it eliminates all sorts of annoying problems with exposed traces between one's microphone and its amplifier and its ADC. I'd love to play around with these more. But, as mentioned above, they're all 24-bit.

    If the Audio library were open to modifications to higher bit rate, the ability to support this new class of microphones would be very interesting.

    Chip

  2. #152
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    Quote Originally Posted by Raj View Post
    Ironically, the sgtl5000's high-pass filter was introducing a lot of high-end noise, so running adcHighPassFilterDisable() helped (and it seems that you do have to run it explicitly it appears to be on by default).
    In testing with my Teensy 3.2 with Line-In (shorted), I get a whining squeal that jitters about. I did the adcHighPassFilterDisable() and that noise goes away. Shocking! Awesome!

  3. #153
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    I'm sorry, but the details of the board you want to use with a Teensy didn't come through with your post.

    I can't see an earlier post in this stream where you have given this information.

  4. #154
    This thread is entirely fascinating, not sure where things stand now with supporting the board in the Audio Library? I'd be interested in one of the free boards Paul is offering but I assume they have all been claimed?

  5. #155
    Administrator Robin's Avatar
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    Quote Originally Posted by cymaspace View Post
    This thread is entirely fascinating, not sure where things stand now with supporting the board in the Audio Library? I'd be interested in one of the free boards Paul is offering but I assume they have all been claimed?
    I have one board left. Follow the instructions that were posted earlier in this thread and you can have it.

  6. #156
    Quote Originally Posted by Robin View Post
    I have one board left. Follow the instructions that were posted earlier in this thread and you can have it.
    Done! Order: 262068. Thank you Robin, looking forward to building this.

  7. #157
    Hi! I am glad to find there's better option than the ordinary Audio board,
    I would like to stream to my PC 3 mics (piezo sensors), 24bit 96Khz, Is there an option to use this boards to this mission?
    Is there any similar project someone did?

    Thanks a lot!

  8. #158
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    To document my own experience with the noise of the Teensy Audio Board (and to show the positive effect of disabling the SGTL5000 ADC's high-pass filter), I wrote it up here:

    http://openaudio.blogspot.com/2017/0...elf-noise.html

    Audio samples are shared on that page, along with spectra comparing "with HP" and "without HP". That high-pass filter is adds a lot of squeeling whiney noise!

    Click image for larger version. 

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    Click image for larger version. 

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    Chip

  9. #159
    Senior Member PaulStoffregen's Avatar
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    I've added a link to your blog article to the SGTL5000 documentation.

    https://github.com/PaulStoffregen/Au...a807200037d85c

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