• Hardware

  • 96kHz Audio Channels on Bela Mini

Hi there!

I'm attempting to run audio channels at a 96kHz sample rate, rather than the default 44.1kHz. I don't need digital or analog I/O so I don't need that synchronization.

I've looked through these threads:
https://forum.bela.io/d/46-24-bit-audio-input-output-48khz
https://forum.bela.io/d/242-how-to-achieve-a-different-sampling-rate

So far I've been able to achieve 48kHz by simply changing the code in I2c_codec.cpp line 115 to:
if(setAudioSamplingRate(48000))

This generates the following clock PLL parameters:
MCLK: 24.0000 MHz,
fs(ref): 48000.0000,
P: 2,
R: 1,
J: 8,
D: 1920,
NCODEC: 1.000000,
Achieved Fs: 48000.000000 (err: 0.0000%),

This plays back the "sinetone" project at around 480Hz which one would expect.

However, setting that same line to if(setAudioSamplingRate(48000)) yields this error:
I2c_Codec: error, no valid PLL settings found

I assume the PLL settings function isn't really designed for that sample rate...

FYI I'm completely new to C++ and the Bela platform - hoping to use RNBO to do all the hard work 🙂

Any help is greatly appreciated, thank you!

    arimassias However, setting that same line to if(setAudioSamplingRate(48000)) yields this error:
    I2c_Codec: error, no valid PLL settings found

    You mean 96000?

    It won't work that way, but it should be as easy as setting params.dualRate = 1. It won't be reflected in context->audioSampleRate I believe, so the pitch would change

      Oh yes, I meant 96000 throws the error, good catch.
      So I should keep the code to set to 48k (if(setAudioSamplingRate(48000))), while enabling dualRate?
      I can't seem to get the params. to make any changes at the top of the code - only by hardcoding changes to the statements that call them later on, such as with setAudioSamplingRate
      How can I change the lines 152-159 to enable dual rate?
      if(params.dualRate) {
      if(writeRegister(0x07, 0xEA)) // Codec datapath register: 44.1kHz; dual rate; standard datapath
      return 1;
      }
      else {
      if(writeRegister(0x07, 0x8A)) // Codec datapath register: 44.1kHz; std rate; standard datapath
      return 1;
      }

      Hi @giuliomoro,

      I made some changes, though I'm not sure if I've achieved 96kHz.
      In I2c_Codec.cpp:
      if(params.dualRate) {
      // if(writeRegister(0x07, 0xEA)) // Codec datapath register: 44.1kHz; dual rate; standard datapath
      if(writeRegister(0x07, 0x6A)) // Codec datapath register: 48.0kHz; dual rate; standard datapath
      return 1;
      }
      else {
      // if(writeRegister(0x07, 0x8A)) // Codec datapath register: 44.1kHz; std rate; standard datapath
      if(writeRegister(0x07, 0x0A)) // Codec datapath register: 48.0kHz; std rate; standard datapath
      return 1;
      }

      In I2c_MultiTLVVodec.cpp (I'm running a Bela Mini with the multichannel expander):
      params.dualRate = true; //false;
      params.samplingRate = 48000;//44100;

      This produces:

      When playing the sinetone project, I dont get any pitch shift as I would expect, but it seems like these are the correct registers to hit 96kHz.. Is there a better way to test this?

      I imagine the read out says 48kHz because the code doesn't update the PLL denominator to 1024 instead of 2048 in dual-rate mode, so I guess I'm not too worried about that.

      Using the dev branch, the following works for me to get the audio running at 96kHz on BelaMini. h:

      diff --git a/core/I2c_Codec.cpp b/core/I2c_Codec.cpp
index edb05e60..5af785e6 100644
--- a/core/I2c_Codec.cpp
+++ b/core/I2c_Codec.cpp
@@ -37,12 +37,12 @@ I2c_Codec::I2c_Codec(int i2cBus, int i2cAddress, CodecType type, bool isVerbose
        params.slotSize = 16;
        params.startingSlot = 0;
        params.bitDelay = 0;
-       params.dualRate = false;
+       params.dualRate = true;
        params.tdmMode = kTdmModeDsp;
        params.bclk = kClockSourceCodec;
        params.wclk = kClockSourceCodec;
        params.mclk = mcaspConfig.getValidAhclk(24000000);
-       params.samplingRate = 44100;
+       params.samplingRate = 48000;
        initI2C_RW(i2cBus, i2cAddress, -1);
 }

@@ -1164,7 +1164,7 @@ unsigned int I2c_Codec::getNumOuts(){
 }

 float I2c_Codec::getSampleRate() {
-       return params.samplingRate;
+       return params.samplingRate * (1 + params.dualRate);
 }

 int I2c_Codec::setParameters(const AudioCodecParams& codecParams)

      The second change makes sure the correct value is reflected in the BelaContext, so that your oscillators etc should be in tune. Things will be different when running with a Bela RevC cape on BeagleBone Black, but for the Mini this should be all you need.

      If you run the program with analog enabled you'll predictably get McASP underrun messages, so make sure you run it with analog disabled (which will also disable the I/O of the digitals I think).

      Thank you @giuliomoro! I had the multichannel expander attached (https://shop.bela.io/collections/multichannel/products/bela-mini-multichannel-expander-starter-kit) so I believe it was calling a separate codec script and not using the parameters in I2c_codec.cpp? Once I removed the expander, the Bela Mini ran at 96kHz. I'll keep trying to get the expander to work at 96kHz but I should be good to move forward with my project now. Thank you for the help, I really appreciate it!

        arimassias I had the multichannel expander attached

        Oh I went with the thread's title ... That one calls I2c_MultiTdmCodec.cpp I believe.

        arimassias I'll keep trying to get the expander to work at 96kHz but I should be good to move forward with my project now.

        I doubt that will be possible. IIRC, the TLC320AIC3104/6 can only generate bitclock in I2S mode at that rate, but the wiring of the codecs in the Mini Multi is for TDM (all input data lines are shared by all codecs, all output data lines are shared by all codecs).