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Instabel 88 kHz S/PDIF output with the ADAU1452

Question asked by Jan-Meier on Feb 1, 2017
Latest reply on Feb 8, 2017 by DaveThib

Currently I'm working on an audioprocessor-design that incorporates the ADAU1452. The design is being made/tested/evaluated using SigmaStudio and the EVAL-ADAU1452MINIZ evaluation board.

 

The ADAU1452 runs in slave mode. Input is a serial I2S signal of various sampling frequencies.

 

Output is a serial I2S signal send to an added DAC-chip (the on-board DAC-chip of the evaluation board does not accept all possible sampling frequencies in its present configuration). As a second output channel the optical S/PDIF transmitter is used. The added DAC-chip runs in slave mode to the input signal.

 

This setup runs fine at all common sampling frequencies (32, 44, 48, 96, 192 kHz) with one exception. Whereas the output signal of the added DAC-chip looks fine at 88 kHz the output of the S/PDIF transmitter seems to be compromised. Using an external DAC-device (with a WM8804 S/PDIF receiver) results in loss of signal-lock several times per second, causing interruptions of the audio-signal. With other 88kHz sources this external DAC-device has never shown any problems. Also all other sampling frequencies lock fine without any interruptions.

 

I checked the signal chain

 

Chip output S/PDIF <> Optical transmitter <> Optical receiver

 

and found no problems. I also tapped the S/PDIF output signal directly at the ADAU1452 and send it by coaxial connection to the external DAC. The same problem occured. No continuous lock at 88kHz.

 

As only this specific frequency is involved my suspicion is that the problem might be related to a "clocking issue" but I have no real clue on how it can be solved. Do people have any suggestions??

 

Cheers

 

Jan Meier

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