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PCM270X sample rate

Siavash Rezaei
Prodigy 80 points
Other Parts Discussed in Thread: PCM2706, PCM3070

Hi,

I like to use PCM2706 or PCM2707 in one of our products for their I2S output.

It would make our design much simpler, if we could fix the sample rate at 48kHz.

Is it possible to configure it such that it only supports 48kHz?

Thanks,

  • 0
    TI__Guru** 109545 points
    Hi Siavash,

    PCM270x is slave to USB audio data. So nothing is done to the part to set its sampling frequency. It tells the operating system what it can support, but it derives the audio clocks from the USB audio data coming in. Those audio clocks can then be sent out on the I2S bus. If the operating system converts the USB data such that 44.1kHz comes into the PCM2706, then a 44.1kHz sampling frequency will come out.

    One way to force 48kHz on the PCM2706 could be to use an external ROM and set non-standard product/vendor ID for the PCM2706, then creating a separate driver file that only specifies 48kHz as an acceptable frequency. But we haven't developed an application like this before.

    Best regards,
    Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 80 points

    Hi Ivan,

    Thanks for the information.

    I have another question regarding sample rate of PCM2707. How do I find out which sample rate it is working at? I need to know this to switch coefficients on a PCM3070 that is receiving samples from the I2S out of PCM2707.

    Thanks,

  • 0 in reply to Siavash Rezaei
    TI__Guru** 109545 points
    Hi Siavash,

    The input USB data frequency should be followed to the output.
    You should be able to measure fs at LRCK, its period T is T = 1/fs

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 80 points
    Hi Evan,

    I think I didn't phrase my question correctly.
    What I meant was, how would my MCU know which sampling rate is coming from PCM2707?
    My MCU needs to know the sampling rate so it can update the coefficients in PCM3070.

    Thanks,
  • 0 in reply to Siavash Rezaei
    TI__Guru** 109545 points
    Hi Siavash,

    Unfortunately there is no notification nor setting option for sampling rate. This device is passive and will operate according to the information acquired from the USB host. I think you can use 44.1kHz, which is the default setting, as long as there is no change in sampling rate from the host.
    Another option could be a sample rate converter like SRC419x which can be configured as slave for PCM2707 and slave or master for PCM3070.

    Best regards,
    -Ivan Salazar
    Texas Instruments