Very strange A/V issue with new Macbook Pro

Discussion in 'MacBook Pro' started by evilphant0m, Feb 25, 2011.

  1. evilphant0m macrumors newbie

    Feb 25, 2011
    So I just got one of the new 15 in macbook pros yesterday and I've fully integrated it into my home theater system. I've got a mini display to hdmi adapter making my hdtv a second monitor, and I've got the line out audio running into my audio receiver. The odd issue is that when I have the line out audio and the mini display adapter plugged in at the same time, I pick up what sounds like a eastern-european/middle-eastern radio station over the sound system. However, if I unplug the audio cable the radio does not play over the mac's internal speakers and when I unplug the mini display to hdmi adapter the sounds also disappear and all I hear over the sound system is my mac's audio. Does anybody have any idea whats going on?
  2. JNL Productions macrumors member

    Nov 12, 2010

    Very strange, is there a radio playing through your home theater system or any external audio source that's connected along with your MBP?

    Very interesting...
  3. evilphant0m thread starter macrumors newbie

    Feb 25, 2011
    nope, I dont even have the radio tuner plugged into the receiver.
  4. ComputersaysNo macrumors 6502


    Apr 15, 2010
    It sounds like you have two outputs connected to eachother. For example: The audio output of an Ipad to the audio output (tape out) of a receiver.
  5. evilphant0m thread starter macrumors newbie

    Feb 25, 2011
    Do you have any idea how I would find/fix this issue? Also, I just found a matching station on my clock radio and its an AM station.
  6. benpatient macrumors 68000

    Nov 4, 2003
    When I plug my 2007 white macbook into my digital t-amp (with a standard stereo 1/8 male plug) and don't send it any kind of signal (macbook on, amp on, but no actual audio signal coming from the laptop), I pick up a religious AM radio station on the amp.

    I think it is using the macbook case as an antenna for AM radio. There is no radio tuner involved in my setup at all, just to be clear. This is a stand-alone digital amp and a macbook with a stereo jack connecting them.

    It creeped me out for several months, and then i just got over it.

    I don't know a lot about how radio signals work, but since AM radio is based on amplitude, I just figured it must be, well, amplifying that somehow.

    maybe a radio guru could explain it? It can't be an isolated issue.

    have you tried playing a sound on the machine? I noticed that even if i played something very, very quiet on the macbook, the ghost radio station disappears completely.

    I also have an analog baby monitor that picked up a different AM radio station, despite not being AM-based.
  7. Blu101 macrumors 6502a


    Sep 10, 2010
    Sounds like it's using the cable as an antenna. Try plugging in the tuner to see if it filters it out, or (without the tuner) try to lower your gain/volume, since you're not listening to anything (only happens when you're not playing anything, right?).
  8. evilphant0m thread starter macrumors newbie

    Feb 25, 2011
    Actually it does play when I play other audio over my macbook, and its loud enough that its actually pretty distracting(think an itunes track at 1/4 volume). The mac's internal volume doesn't change the signal volume, and disabling the the line in audio input on the mac doesn't help(I thought it might be receiving a bit of audio from the tv through the hdmi). Also, I bought the receiver used so I dont have the tuner.
  9. benpatient macrumors 68000

    Nov 4, 2003
    I think it is likely that your HDMI cable isn't properly shielded, and you're getting some RF amplification from it.

    How long is your HDMI cable?

    Do you have another one you could swap out for that one, maybe a different brand, or shorter?

    shorter is better in this case.

    Also, does the problem persist when you disconnect your laptop from the magsafe cable?

    You might need a ferrite choke for your HDMI cable.

    Ferrite choke

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