How to set ADAU1701 HW/SW to adapt different sample rate signals?
Hello ADI engineers,
In developing ADAU1701 with external I2S PCM input, I meet problems in setting Hardware/ software for 96khz/ 192khz sample rate.
The default setting in EVM is:
MCLK 12.288mhz, PLL_Mode:01(256xfs), 48khz sample rate in Sigma software interface.
It works well when external I2S rate is 48khz.
Question1: if I want to use 24.576mhz Oscilator as MCLK (for 48khz rate input signal), how should I adjust PLL_Mode and Software sample rate? Is it 11(512xFs)for PPL_Mode under all conditions? And all I need to do to change sample rate is to set the software sample rate, right?
Question2: does internal DAC and ADC of ADAU1701 support 96khz and 192khz sample rate?
Further, I use an external ADC as Digital source and the internal DAC for output.(MCLK:24.576MHZ, PLL:11(512fs)) But whenever I set software rate as 48khz, 96khz, 192khz, the 96khz and 192khz digital source cannot work in internal DAC. Is this because internal DAC does not support 96khz and 192khz sample rate? Waiting for your response.
Kind regards,
Louie
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
Hello Louie,
The internal DAC and ADC does support 96K and 192K rates. The DSP core will run at 192kHz rate. The registers have to be properly setup.
You can use a 24MHz if you setup the PLL Mode correctly. The 512x and 256x numbers are for an assumed 44.1/48kHz sample rate. So 24,.576MHz divided by 48kHz gives you 512 so 512 is the correct PLL Mode setting. When you change the sample rates of the converters the internal dividers will change to supply the correct frequencies so no need to change the PLL Mode.
When you are using an external serial port signal and you are supplying the clocks, not the ADAU1701, then those clocks MUST be in sync with the master clock that is being supplied to the ADAU1701. This part has an unusual behavior in that as soon as clocks are supplied to the serial port, the internal clock system switches over to it and then if it does not properly divide into the master clock it will mute the DACs. If it is close then it will mute and unmute the DACs depending on the difference which can create some interesting distortions or muting unmuting behavior.
This may be what you are experiencing.
Dave T
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