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  1. #1
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    Mar 2008
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    Wandboard Muffled S/PDIF Audio

    This is a really odd one: A friend of mine is using a Wandboard Quad as his server and player, feeding his receiver via the Wandboard's built-in optical S/PDIF output.

    It plays DTS material just fine, which would seem to suggest that the output is, as expected, bit-perfect.

    But...standard PCM material has a very obvious muffling/rolloff of the highs. I don't mean some kind of we-had-to-strain-to-hear-the-difference self-proclaimed audiophile nonsense, but in fact a very obvious and non-subtle rolloff. We tried multiple tests to make sure we weren't nuts including syncing two players (the other a Pi via HDMI) and switching back and forth. The difference was blatant.

    Thinking there may have been some odd setting going on in his receiver, we played a CD on a standard CD player and, via the Wandboard, a rip of the same CD with no alteration (i.e., ReplayGain turned off). We moved the same optical cable back and forth between the Wandboard and the CD player and again the difference was quite obvious.

    How is this even *possible*? I can understand how maybe the optical output of the Wandboard could go bad, though in that case I'd expect the incredibly delicate DTS stream to just produce noise. Certainly neither LMS nor Squeezelite would even know the difference between PCM and DTS, so they wouldn't be doing something different with the output depending on what was getting played.

    I've got multiple Wandboards myself and have never experienced anything like this. When he told me about it over the phone I smugly thought either he was crazy or his receiver was doing something, but after the CD player test I'm convinced that there really is a problem...I just can't figure out what it could possibly be!

    Any ideas?

  2. #2
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    Mar 2008
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    Quote Originally Posted by atrocity View Post
    Thinking there may have been some odd setting going on in his receiver, we played a CD on a standard CD player and, via the Wandboard, a rip of the same CD with no alteration (i.e., ReplayGain turned off). We moved the same optical cable back and forth between the Wandboard and the CD player and again the difference was quite obvious.
    Still have no idea what's going on here, but he "fixed it" by getting a HifiBerry Digi+ and making the Pi the player.

  3. #3
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    Mar 2008
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    Now *I'm* experiencing this.

    I've synced a Wandboard Quad and a Squeezebox Touch. Both are connected digitally to the same receiver. When switching the inputs back and forth, the high end is CLEARLY significantly degraded from the Wandboard compared to the Touch.

    Even weirder: I hear the same thing with a DTS signal, which should be completely impossible. Denon receiver is set to "DIRECT" for both inputs, so in theory there's no additional processing on either input.

    It *has* to be something stupid that I'm doing and not seeing, but I just can't figure it out.

  4. #4
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    Mar 2008
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    577

    De-Emphasis?

    As a test, I'm playing the original non-de-emphasized files off the original US Columbia CD of Pink Floyd's "The Wall" on the Wandboard and, more or less in sync, the same rip after having been de-emphasized by SoX.

    And they sound pretty similar.

    Is it possible that for some reason the Wandboard is setting the pre-emphasis flag and, if so, how the heck would I turn that off?

    Of course, I'm not sure that explains why I'm also hearing the highs rolled off on DTS material, though I suppose it's possible that the receiver is set up in such a way as to respect the pre-emphasis flag and apply the de-emphasis after DTS decoding. It seems like an odd thing to program, though.

  5. #5
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    Mar 2008
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    The fix is as simple as:

    Code:
    iecset emphasis 0

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