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iPod/USB/Display Audio/JBL Sound glitches

Discussion in 'Gen 3 Prius Audio and Electronics' started by HprDad, Nov 14, 2012.

  1. HprDad

    HprDad Junior Member

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    Here's the setup:

    2012 Four, Display Audio w/ JBL, iPod touch 4th gen, playing music over USB, apple cable.

    Here's the problem:

    During quiet passages in music, I hear glitches, similar in sound to high frequency pops and clicks you'd hear on an old LP. They're subtle, but clearly there, especially noticeable with the good JBL front tweeters. I first noticed this on the highway, when listening to "Shine On You Crazy Diamond", but dismissed as road nose. After hearing it on other songs, including "As Falls Wichita, So Falls Wichita Falls", I started investigating. It is quite audible, especially when running in town on EV, or when sitting at a stop, with the car "ready". The glitches aren't periodic, but vary from every few seconds to perhaps only a couple a minute. The same exact songs on this iPod don't exhibit the issue when using the car's AUX input. Just to be sure, I also played the original CDs in the car, and they're fine. I've encountered this on three different albums now, some encoded with MP3, some with AAC. Bit rates are MP3/192, AAC/256VBR, all ripped from iTunes with error correction enabled.

    This makes me think there are issues with the CODEC in Toyota's head unit, perhaps with these bit rates. I haven't come across this in any searches here, or on the apple site, though there seem to be some reported issues of drop-outs, which I haven't experienced. Next, I'll experiment with a different cable, different bit rates, and some purchased AAC files. Any other suggestions? Anyone else suffer from this problem, or hear of such an issue?

    For now, I simply use AUX for certain albums, but I'd sure prefer to use the USB functionality!
     
    #1 HprDad, Nov 14, 2012
  2. SageBrush

    SageBrush Senior Member

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    Start with the simple things: check the cable connections, and if that does not help, try a different cable.
    If that does not solve things, try encoding at a bit lower rate, say 128. I'd also avoid VBR until I knew it was not the problem.

    Good Luck
     
    #2 SageBrush, Nov 14, 2012
  3. HprDad

    HprDad Junior Member

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    Tried a 2nd new apple USB cable, same issue. I would have been surprised, but hey, had to try this first. Onto testing different bitrates. The owners manual says the system supports up to 320 Kbps mp3, and VBR. Doesn't specify what AAC bitrates are supported, but the apple store has been using 256 VBR for three years, so it would be pretty surprising if it couldn't handle this.
     
    #3 HprDad, Nov 15, 2012
  4. SageBrush

    SageBrush Senior Member

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    hmm
    When you say the song sounds fine using the AUX, does that mean the iPod is performing a D/A conversion on the encoded material before sending out an analog signal ?

    In the interests of solution by elimination, I suggest playing a song with different encoded formats from a USB stick. You might also want to try playing a non-compressed song through USB.
     
    #4 SageBrush, Nov 15, 2012
  5. Zephyr7

    Zephyr7 Member

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    you are using Display Audio with Navigation right?
    Are you running SW 2.1.0?
    Do try with USB stick and do share your findings!
     
    #5 Zephyr7, Nov 16, 2012
  6. HprDad

    HprDad Junior Member

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    Today's update. Yet another old jazz album was clicking a bunch this morning, so tried a simple thing I hadn't thought of before. Turned off audio & rebooted the iPod. Glitch free ride the rest of the way!

    Perhaps there was a rogue process in the iPod taking away too much CPU time from the USB streaming, or simply a bug in the OS. USB protocols are fairly CPU intensive, unlike Firewire that used to be in iPods (wish that would have become the standard!). I wonder if iOS devices stream the audio using isochronous mode, or if the Toyota head unit is simply requesting bulk file transfers? Bulk would be far less elegant, but it would have to be used for thumb drives. Time for more research...
     
    #6 HprDad, Nov 16, 2012
  7. SageBrush

    SageBrush Senior Member

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    Nice.
    I was mulling over what the source of the popping sound might be, although I lack any useful electricity experience to help. Certainly the circuity is ends up with a very high gain (amplification,) so I imagine it would not take much of a voltage blip to be heard.
     
    #7 SageBrush, Nov 16, 2012
  8. HprDad

    HprDad Junior Member

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    #8 HprDad, Nov 16, 2012
  9. quakerboy

    quakerboy Junior Member

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    I think you need a ground loop isolator. PAC Ground Loop Isolator for 3.5 MM Applications : Amazon.com : Automotive
     
    #9 quakerboy, Dec 10, 2012
  10. HprDad

    HprDad Junior Member

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    #10 HprDad, Dec 11, 2012
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