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  1. #16
    Audio Input Not Working With One Device
    PGB1's Avatar
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    My understanding reading that article is that you need both applications, the LineIn and Audio Midi are not equivalents, - you set up Audio Midi first and then you select LineIn within the Audio Midi application the way it shows in the article.
    Thanks for that tip! I didn't realize they were different since they appear the same. I'll have to explore more & learn more.

    I think all the "Audio In" (which I think is what Apple calls them) are line level inputs, ie require typically 1 volt rms for full volume.
    That's helpful knowledge for building a pre-amp. For fun, I'll make the output adjustable & ramp up the voltage slowly to see the low sound threshold voltage & the full volume threshold. It should be quite interesting. I'll post what I learn here when I eventually get time to make the pre-amp.

    ... is to use a USB Mike.
    I never knew these existed! I'll keep that in mind if I need a microphone in the future.

    ... 4-pos plug that plus into the headphone jack - don't know if your Mac has that
    Mine's a 3-pole input jack. I can't remember why I needed the jack, but I had to replace it some years ago due to a permanent buzz whenever I set System Preferences to Line In. When I dissected it, I found a contact came loose and shorted to another one.

    Thank You for the extra helpful information! Knowledge Is Power! (Or at least it keeps me from wasting too much time chasing down something that can't work.)
    Last edited by PGB1; Yesterday at 10:16 AM. Reason: Gotta turn up the heat in here. Typing's hard enough without shivering.

  2. #17
    I find that Apple does a lousy job explaining the audio inputs and outputs on the various Macs.
    I could never even find any basic information like input and/or output impedance or signal levels required at the various ports.

    The 4-pos jack/plug arrangement that some Macs use is also not described - one can't even figure out which Macs actually have that type of jack.
    The 4-pos plug/jack is called a TRRS plug/jack - searching for that on google brings up a bit more information but still no listing of which Macs have it and which ones do not.
    A description of the various jack types is here:
    Understanding TRRS and Audio Jacks - Cable Chick Blog

  3. #18
    Quote Originally Posted by krs View Post
    I think all the "Audio In" (which I think is what Apple calls them) are line level inputs, ie require typically 1 volt rms for full volume.
    So to use a typical Mike with that input one would need an amplifier to bring the level up to that.

    However, many Macs have the headphone output wired so it can be used as a Mike input as well. That output jack on those will accept a 4-pos plug like in the attachment
    Apple also offers (or used to) a headset or earbuds with an integral Mike and with a 4-pos plug that plus into the headphone jack - don't know if your Mac has that - something you may want to check out.

    And as to


    My understanding reading that article is that you need both applications, the LineIn and Audio Midi are not equivalents, - you set up Audio Midi first and then you select LineIn within the Audio Midi application the way it shows in the article.
    The advantage over using QT, which also works, is that you don't get that 1/2 second delay that you get when using Quicktime - but maybe the delay is not an issue.

    The other option as far as the Mike is concerned, if you don't already have one you want to use, is to use a USB Mike.
    That would just plug into a USB port

    Attachment 30629
    Thanks, worked for me

    Had the same issue but is resolved now

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