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PCM3060: External vs Internal clock for digital guitar pedal

Diego Conterno1
Prodigy 20 points
Part Number: PCM3060
Other Parts Discussed in Thread: PCM4220, TLV320ADC6140

Greetings,

I am currently working on a digital guitar pedal. I am using an STM32F446RC as my MCU and the PCM3060 as my CODEC, however I was thinking of using instead ADCs (PCM4220, TLV320ADC6140), and DACs (PCM5xxx) from the TI portfolio. The problem I have right now is understanding what would be the best, in terms of reliability, for my clock reference. Should I used the MCU internal clock or should I use an external clock as reference?

I am trying to have 44.1kHz as my sampling frequency, though am still not fully understanding how the is it that if I use an external crystal (25 MHz) then this would bring an error. I would like to understand this concept a lot better. 

How does one pick the correct external clock frequency that's best suited for the MCU and the application? 

How is the MCU processor's frequency (180 MHz ) is relevant? 

Thank you in advance, 

D.C. 

  • 0
    TI__Guru 63185 points

    Hello,

    For a higher performing system, like the one you're building out of the devices listed, we typically see customers using an external crystal to achieve the low-levels of jitter desired to achieve optimal audio performance.  Or they're using a peripheral from the controller that is still based on a crystal input for good low-jitter operation.

    Many audio devices only have internal dividers between the main MCLK (SCLK) input and the resulting BCLK and FS outputs. Therefore, the MCLK must be an integer multiple of the outgoing sampling rate for operation to occur function properly.  Other devices, like the TLV320ADC6140 have internal PLL circuitry which enables them to accept non-integer multiples of MCLK/BCLK relative to the outgoing BCLK/FS signals.  Devices with an internal PLL are a little more resilient against jitter on the input since the PLL will filter some of it.

    Note many new Audio devices, like the TLV320ADC6140 operate fine from a 3-wire audio serial interface (ASI) bus and only require BCLK, FSYNC, and Data.