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Author Topic: Macbook/RFI  (Read 2137 times)

Stephen Swaffer

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Macbook/RFI
« on: November 02, 2014, 04:21:30 pm »

.Very similar to previous thread abotu camera/rfi, but so as not to hijack the thread I will separate it.

I have been using the same audio setup with an iMac for sometime-headphone jack to to line inputs on our A&H GL3800. Occasionally had issues with hum, got my hands on a 2 channel M audio USB interface a few weeks ago and used it without problems-same mini plug to 1/4 line cord (plan to change just haven't got around to it.)

Last week tried using a MacBook Pro to Skype a missionary from Tanzania (ultimately successfully).  All I could get out of USB interface was our local AM station  Plugged into headphone jack and had a hum which went away by either reversing polarity on one channel, or only turning volume up on one channel (final solution).

This week same setup.  Headphone jack gives me really bad hum only-no work arounds are effective (yes I tried the jack multiple times.)  USB works perfect this week.

USB interface is USB powered.  The only difference is this week we ran off battery only on Macbook-no charger connected.  Last week we tried disconnecting charger with no change.

Could the charger cause this?  MacBook was given to be used as a media computer for us, so I need to find a way to get consistent results. 
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Steve Swaffer

Mac Kerr

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Re: Macbook/RFI
« Reply #1 on: November 02, 2014, 04:39:50 pm »

I have been using the same audio setup with an iMac for sometime-headphone jack to to line inputs on our A&H GL3800. Occasionally had issues with hum, got my hands on a 2 channel M audio USB interface a few weeks ago and used it without problems-same mini plug to 1/4 line cord (plan to change just haven't got around to it.)

The mini plug to 1/4" cable implies an unbalanced interface. Get thee to a balanced interface! Two I have had good luck with are the Black Dog USB DI and the Peavey USB-P. The Peavey doesn't have as robust transformers as the Black Dog, which may mean less headroom at low frequencies, but they both work for me. I own the Black Dog for my personal kit, but have used both.

Mac
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Stephen Swaffer

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Re: Macbook/RFI
« Reply #2 on: November 02, 2014, 05:52:31 pm »

The m-auio has balanced I/O-just haven't found cables to change over-do what I know to do first right?

I am actually about to pull the trigger on a Scarlett 18i20-I would like multiple channel playback capability to use with Q lab for a theatrical production.  Unless any better suggestions?
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Steve Swaffer

Rob Spence

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Re: Macbook/RFI
« Reply #3 on: November 02, 2014, 06:51:56 pm »

Which M-audio interface are you using?

Use a DI for consistency.


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Stephen Swaffer

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Re: Macbook/RFI
« Reply #4 on: November 02, 2014, 07:09:17 pm »

It is a Mobile Pre.  Has TRS outputs-can't find specs on line so they may not be balanced.  Tried again tonight-charger is definitely creating hum issues-even after dumping the miniplug to 2 line ins and using a pair of TRS cables.
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Steve Swaffer

ProSoundWeb Community

Re: Macbook/RFI
« Reply #4 on: November 02, 2014, 07:09:17 pm »


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