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PCM1792A: Hi-Res phase shift starting at 5kHz/192kHz to 20kHz/192kHz

Jim Michelson
Prodigy 30 points
Part Number: PCM1792A

Can you tell me why I'm consistently seeing a stereo 20 kHz sine wave with no phase shift between L/R with 48 kHz or 96 kHz, but the same signal has ~ -37.41° shift with 192 kHz.

Also, testing at various frequencies show the following results, (all at 192kHz sampling)...

@ 1kHz, I see about a -1.5° phase shift; @ 5kHz a -9.36° shift; 10kHz a -28.08° shift

Best Regards,

Jim

  • 0
    TI__Guru 57800 points

    Hi, Jim,

    Welcome to E2E, Thanks for your interest in our products!.

    Could you please provide more details about how the phase is being measured?. Is this phase mismatch present in all the outputs of the part?. We will take a look to this and will get back to you as soon as possible.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 30 points
    Hello Diego,

    Thanks so much for your response.

    There is a phase difference between left/right channels.
    The phase mismatch is measured in a two channel stereo set up. The tests are showing a phase difference between L and R channels, only when playback of a file in 192kHz sampling rate (signals of 1k, 5k, 10k, 15k, 20kHz) is being tested.

    We have measured with an AP ATS-2 calibration analyzer. The same phase issue has been verified with an AP x500 analyzer.
    We are also using a scope to view the phase differences within the waveforms, in relation to left/right channels.

    The ATS-2 gives us the degree of phase shift between left and right channels at the chosen frequencies.

    Testing a signal with a 96kHz sampling , we find, this is not the case.

    It will show even greater phase shift with a 20kHz signal at 176kHz sampling ; example- 20kHz/176kHZ sampling, there is ~ a 40° shift.

    Regards,
    Jim
  • 0 in reply to Diego Melendez
    Prodigy 30 points
    Hello Diego,

    Thanks so much for your quick reply.

    We measured using an AP ATS-2 and an AP x500. We also used a scope to see the phase differences between the left and right channels.
    The AP's showed us the degree of phase difference between the two channels, with the x500 being able to also show the waveform.

    The audio files at 196kHz sampling, were input to our device using a coaxial digital audio cable and into the PCM1792A.

    We also tried the same testing on a PCM1795A chip, which demonstrated these same results.

    Any insight would be appreciated.

    Best Regards,
    Jim