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ADAU1401 : 192KHz Sampling of S/PDIF from eval board: high freq distortion?

Question asked by ImranKhan on Oct 3, 2012
Latest reply on Oct 11, 2012 by ImranKhan



I'm trying to use the S/PDIF input and output on the ADAU1401A-EVAL board, running at a 192kHz Sample Rate.


I've got the system working with slower sample rates (48, and 96 kHz specifically), however when I use 192kHz I get a very strange frequency response, almost like a weird aliasing artifact.


I've attached my project and examples of the distortion. The project is setup to do just a straight passthrough from the inputs to the outputs. I've gone through and set the switches and jumpers as described in Table 7 of the Eval Guide.


20hz-96khz Freq Sweep 192khz Fs.bmp shows the output as level vs. frequency for a 20-96Khz frequency sweep. That should be a straight line (See 20hz-64khz Freq Sweep 128khz Fs.bmp for expected output).


64Khz Input Tone at 192khz Fs.bmp shows an FFT of the response to a 64 kHz input tone.


64Khz Input Tone at 128khz Fs.bmp shows an FFT of the response to an 64 kHz input tone sent by a generator running at 128 kHz Fs.


I'm using an Audio Precision to generate (and analyze) sample tones encoded as 24 bit S/PDIF over coaxial cable.


Any suggestions for ironing this out?


Thanks in advance.


Imran Khan