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PCM to I2S?

Other Parts Discussed in Thread: PCM1794A, PCM5102A

I am using a PCM1794A for a design. The device take I2S data.

I have another device that is outputting PCM data, how do I take the PCM data and convert it to I2S that has: MCLK, BCLK, DATA, WCLK

Can the PCM1794A run directly from PCM data without having an MCLK?

Thanks;

  • Moving to audio-converters forum...
  • Hi Lenny,

    All of our devices that have an I2S port will require at least BCK and LRCK clocks that is synchronous with the data in order to operate correctly. In the case of PCM1794A, it also requires a synchronous MCLK. What is the source of the PCM data?

    Justin
  • The Source of the data is Bluetooth module, BM64 from microchip. 

    It looks like a standard I2S interface with out an MCLK. Is there a way to add an MCLK?

    Here is how they define the interface:

    SCLK0 can be 64xFS or 256xFS.

  • It looks like your BT module can generate 256xFS sck. If yes, that you can connect them to mclk and divide by four for generating of BCK signal.

    Other option is to use another DAC which doesn't require MCLK signal like PCM5102a.

  • I am stuck to using the PCM1794A, it is the only DAC that gives level of performance that I need. On a separate note can you recommend a divide by 4 circuit, that will keep proper phasing.
  • Hi Lenny,

    What performance are you looking to hit? If using a bluetooth connection, unless it is the aptX HD profile, the audio will be 16 bit 44.1 kHz and this will be limited to -96 dB SNR theoretically, about -90 dB SNR practically. Are you planning on using, or being capable of using a profile that provides better audio transfer than the base aptX?

    As for Pavel's suggesting, the issue with this is that the data from the BT module will still be clocked out at 256*Fs, and the PCM1794A will be expecting the data at a slower rate, which will cause errors.

    You could use a device such as the SRC419X that can take in an I2S signal that is just BCK LRCK and data, and synch it to a master clock taht is created by a crystal, which then could be sent to the PCM1794A with an MCLK, LRCK, BCK and data.

    Justin
  • Justin,

    The Bluetooth module can output 24-bits, at either 48k or 96k sampling frequency. I have another setup with the PCM1794A that is giving me 125dB SNR and 0.0004% THD, using an S/Pdif to I2S converter with 24 bit and 48kHz.

    I am looking to achieve the same numbers with the Bluetooth setup.

    Can you please suggest a circuit that I will need to get I2S properly to the PCM1794A from the Bluetooth module.

    Thanks;