MacBook Pro 13" (Mid 2010) audio jack

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Level 1

10 points

MacBook Pro 13" (Mid 2010) audio jack

Hi,
I have MacBook Pro 13" (mid 2010) machine, and unfortunately it has only one audio port (both for input and output).

I want to use the same audio jack both for input and output (Guitar + Headphones). I've bought a 4 contacts 3.5 mm plug, and successfully connected my Guitar and my Headphones to the computer (the Sounds Preferences successfully recognized that I'm using both headphones and external input source).

I can hear computer sounds (music/videos) and while watching the input volume meter in Sound Preferences I can see that my guitar sends the correct signals.

The problem is that while launching GarageBand there's a constant feedback sound, volumes levels looks high and the no guitar sound is getting through.

Someone succeeded in connecting audio input and output using this method ?

Unibody MacBook Pro 13", Mac OS X (10.6.5)

Posted on Nov 26, 2010 3:18 AM

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Answer 1

eww

Level 9

53,040 points

Nov 26, 2010 4:46 AM in response to Yaniv4

You can't use the single audio port for input and output at the same time. You'll need a USB or FireWire audio interface to use for one or the other. An inexpensive unit that would serve the purpose is the Griffin iMic:

http://www.amazon.com/Griffin-iMic-Sound-card-stereo/dp/B000BVV2IC/ref=sr11?ie=UTF8&qid=1290775541&sr=8-1

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Answer 2

Yaniv4 Author

Level 1

10 points

Nov 26, 2010 6:05 AM in response to eww

Hi, thanks for you reply,

There is a way of using it for output and input, see the iPhone headphone+mic, you can use it with the Mac and it will recognize both external input and output and the mic will work.

The problem with external USB audio devices, is that there is a high latency between the input and the output.
Because I'm using a guitar as my input, I need a minimum latency which the Core Audio of the Mac gives me, this is why I'm trying to use Mac's Core Audio.

Message was edited by: Yaniv4

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Answer 3

Nov 27, 2010 12:35 AM in response to Yaniv4

I've used an iMic to do what you are trying to do and there is no audible latency.

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Answer 4

Dec 1, 2010 3:11 PM in response to Yaniv4

I'm trying to resolve the same problem, and may end up going with an
inexpensive Firewire audio interface.

Anyway, congratulations on building an adapter and getting input and output
to work! The problems you are having are all typical audio feedback behavior.
That is, the track in GarageBand is set to record, so it is outputting
the incoming audio.

You can get a similar feedback by using no cables, just the built-in
mic and speakers and set the track's Monitor to On. In that case the
feedback is happening in the air between your built-in and the built-in mic.

It's strange that you seem to be getting feedback through
the connector itself. (?)

One workaround would be to turn monitoring off on the guitar track,
and just listen to the guitar acoustically, possibly with only
one headphone on.

Another workaround would be to get a USB interface with zero-latency
monitoring. Here's one:
http://www.bhphotovideo.com/c/product/422094-REG/BehringerUCA202_UCA202_USB_AudioInterface.html
It says it can mix the input and output to your headphones.

One weird thing is that in Sound Preferences, you have to choose
whether the audio port is for Sound Input OR Sound Out. Yet they
both work at the same time if you use an iPod headset+mic.

Of course, we can't answer this question by asking Apple....

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Answer 5

Dec 1, 2010 4:10 PM in response to stuckfootage

Here's another example of what you did:
http://h4xx3r.co.uk/?ref=news&subaction=showfull&id=1277159035&archive=&start_fr om=&ucat=&

I just learned that, when you plug in a tip-ring-ring-sleeve plug
into the Macbook audio jack, the menu in Sound Preferences adds
an option to use in and out at the same time.

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Answer 6

Yaniv4 Author

Level 1

10 points

Dec 1, 2010 10:56 PM in response to stuckfootage

Hi,
I finally understood why when launching GarageBand the computer start sending "feedback" like sounds.

The reason for all of that, is that when you plug a *4 contacts plug* to the audio input/output the OS thinks you are using a microphone as an *external input*, there is no way changing this at the sound preferences (nor the audio midi setup).

Because the computer thinks that a microphone is attached it automatically applies a microphone boost to the machine, and the guitar sound is being amplified once by the OS and once by the software itself.

When plugging a regular *3 contacts plug* and choosing the jack as input, you can see in sound preferences that it is using *External Line-In* not *External Microphone* as you will see when you are connecting the 4 contacts plug.

Becuase it is a software issue (not hardware) I wonder how hard should it be to tell the OS that when you're using a 4 contacts plug use the input as *External Line-In* and not as *External Mic*.

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Answer 7

Dec 2, 2010 3:37 PM in response to Yaniv4

Oh I see what you mean. I got one of these cables to test:
http://www.amazon.com/Hosa-Visual-Camcorder-Conductor-Connectors/dp/B0010CTHKQ
and I see how the input switches when you plug it in.

I doubt anyone is going to come up with a software hack anytime soon,
so you should figure out a way to reduce the level of your guitar
to approximate microphone level to avoid the feedback.

If you plug the output of your guitar's effects boxes into a mixer,
that should be work. In fact, many Mackie mixers have an option
to set the Main Out to microphone level.

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Answer 8

Dec 3, 2010 3:05 PM in response to stuckfootage

This device has an attenuator to reduce input audio to mic level:
http://www.kvconnection.com/product-p/km-iphone-xtrs-a22.htm

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