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TLV320AIC3204: TLV320AIC3204 I2S vs PCM audio question

Part Number: TLV320AIC3204

Hi,

I want to tie a TDK/Invensense ICS-43434 MEMS microphone to a TLV320AIC3204 CODEC.

At the moment, I am providing the MEMS with a 1.024MHz BCLK and a 16kHz WCLK. In return, I the MEMS outputs an I2S signed 24-bit 16kHz MSB audio. This is fixed and cannot be changed. The BCLK must be 64x the WCLK. The output will always be 24 signed-bit I2S.

Leaving all things aside, how do I convert I2S samples with the above specs (signed 24-bit MSB 16kHz) to its PCM equivalent?

Thanks,

Ben

  • Hello Ben,

    Thank you for reaching out. I2S is already in PCM format. I2S What do you mean by PCM?

    Is there an issue with connecting the ICS-43434 MEMS I2S bus to the codec's I2S bus?

    Please let me know your inputs.

    Best,
    Andrew

     

  • Hi Andrew,

    Sorry for the delay in responding. I have not yet attempted to test the MEMS with the CODEC. My question was more about the I2S data vs PCM data because what I am testing at the moment by using an MCU to provide clocks to the MEMS mic, sampling the mic's data and storing it to an SD card results in garbled audio when the file is opened as raw 24-bit signed PCM in Audacity. Note though that this is 24-bit data @ 16kHz. I can somewhat here myself and it's just super noisy.

    But with an existing circuit I made using an analog mic tied to the AIC3204 and its digital output set to right-justified 8-bit 8 kHz, this works perfectly with the same MCU storing the audio to the SD card; when I open the files as a signed 8-bit 8kHz PCM audio file in Audacity, it's nice and clear.

    So before I went further with this, I just wanted to check if I2S data samples was exactly the same as PCM data samples (despite the fact that I2S requires teh WCLK and BCLK... I was more curious about the data itself). 

    Benoit

  • Hi Benoit,

    PCM and I2S data use the same encoding scheme (unless for some reason Audacity is using A-law or u-law PCM but I doubt it). Can you share with us a scope shot of the I2S clocks and data from the mic as well as the script you are using to configure the device?

    Thanks,

    Jeff McPherson