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Thread: Teensy Audio 24bit 48kHz qustions and more..

  1. #51
    Junior Member
    Join Date
    Jul 2019

    Post Why we need a I2S 32 Bit stream

    Hi all,

    let me explain why a real I2S (32 Bit per channel slot) is very usefull for us. Iīm working at a university of applied sciences and we are teaching audio engineers to get jobs like hardware development for video&audio, electroacoustics and acoustics. We used a lot of signal processing tools so far like DSPs (Sharcs & Sigma DSP), FPGAs and sometimes there is also a teensy. But when we need high quality audio for applications where high SNR is necessary teensy is not the first choice ;-(. But Teensy is very easy to use and sometimes a newby donīt want to handle difficult programming on DSPs when he only wants to implement a single FIR filter. So it would be great to have teensy working with an I2S streams professional ADC/DAC/Codecs use today.

    I came to this problem/thread, because a teensy 3.6 lies infront of me and it will not work with my own super audio board called realHDaudio-Board. I was sure a Cortex M4 could handle it....And now i just realized that teensys I2S stream uses 16 Bit per channel slot instead of 32 Bit like professional converters like the AK5397 (for example) do. My mistake. And the converters stream cannot be changed. Only 24 Bit are used for audio in the 32 stream and that is enough at this time. On my board i can reach around 125 dB of SNR on the ADC and 119 dB on the DAC (all dBA weighted) side including analog circuits. I developed the board to get it "open source" on the platform and it will be available at the beginning of October 2019. Find a short description of this project here:

    What applications need high SNR?
    In my current project, I want to develop a loudspeaker controller to equalize (FIR linear) my active studio monitors. Think about a RME UCX (113dBA) as an output followed by a loudspeaker controller with high SNR which will become inaudible without adding noise. Nice! Another guy here builds loudspeakers every day and he is always looking for cheap possibiltys for active crossover managment. Ideally with digital inputs. Handling clocks will be another problem in this case. In my project mentioned above a 24 MHz clock is needed to use sample rates up to 768 kHz (harebrained, i know). With a 12 MHz master clock only 44,1kHz is possible. To allow clocks from outside (SPDIF Input) there are chips available (DIR9001 for example) which can switch between a crystal clock or SPDIF clock automatically and they can also generate and forward a high master clock (24Mhz). So for clock handling with digital inputs a jumper pad for internal/external master clock can be useful on a new teensy. And when it will be there i will develop and audio board for you .

    Thanks to all teensy developers! I know 32 Bit per slot is not priority for you at the moment and i cannot estimate how much signal processing would be possible with it on the Cortex M4. But i would be excited to find out. If there is time i will have a look into your audio library. Currently I have no idea how big a change would be.


  2. #52
    Senior Member+ Theremingenieur's Avatar
    Join Date
    Feb 2014
    Colmar, France
    The newer versions of the audio library do 32bit/slot which is 64bit/frame, but only in the 2ch version. The 4ch version is still doing 16bit/slot or 32bit/frame and waits for a kind and competent soul (do your ears ring? ) to fork it on GitHub, to upgrade it, ending up with a pull request.

  3. #53
    Junior Member
    Join Date
    Jul 2019
    Oh Yes! They do. Will come back to it on monday 😁

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