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Old 27th September 2011, 06:15 PM   #1
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Default Audio Y Splitter Not Splitting Signal Properly

Hi all,

I have a setup where I take a stereo audio track created in Matlab (L track contains signal, R track contains noise) and present it out through the audio jack on my computer using a 1->2 RCA cable. This RCA cable should split the digital stereo track into 2 separate analog mono tracks for further processing. When I silence one of the analog cables (by unplugging either the L or R) in an attempt to either completely remove the signal or the noise, what I find is I'm left with a track that contains both signal and noise. If I unplug the L track, the remaining track tends to have louder noise than signal, whereas if I unplug the R track, the remaining track has a louder signal than noise. This suggests to me that the signal is somehow being premixed before splitting the stereo track into 2 analog mono tracks. I'm fairly certain the problem isn't the 1->2 RCA cable because I've tried using a simple 3.5mm headphone splitter instead and it does the same thing. I am working on Windows 7 with a Creative SB X-Fi sound card with the following details:

Driver Provider: Creative
Driver Date: 7/7/2010
Driver Version: 6.0.1.1348
Driver Signer: Microsoft Windows Hardware Compatibility Publisher

I would really appreciate any ideas for why the signal is behaving this way.

Cheers,
Jeff
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Old 27th September 2011, 06:46 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

Why are you sending two tracks, one noise only to a mono output ?

I don't understand you post. seems like you've got autogain
on your inputs which ups noise if the input is unplugged.

rgds, sreten.
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Old 27th September 2011, 06:51 PM   #3
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Quote:
...present it out through the audio jack on my computer using a 1->2 RCA cable. This RCA cable should split the digital stereo track into 2 separate analog mono tracks for further processing.
I would expect a 1->2 RCA cable to behave pretty much as you describe.
Quote:
I've tried using a simple 3.5mm headphone splitter instead and it does the same thing
A stereo male to 2x stereo female, or stereo male to L and R female?
If you're fairly certain the signal isn't being summed by the cables, that leaves the computer itself as culprit.
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Old 27th September 2011, 07:10 PM   #4
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You should check the setup of your sound card.
Make sure that the output is set for stereo speakers.
Disable all effects.
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Old 28th September 2011, 12:25 AM   #5
wwenze is offline wwenze  Singapore
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Run X-Fi control panel, disable CMSS.
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Old 28th September 2011, 12:40 AM   #6
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yeah, your dealing with some kind of spatial enhancer. turn off all effects
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Old 28th September 2011, 12:43 AM   #7
Enzo is offline Enzo  United States
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And if your audio card has any mixer controls, make sure both L and R signals are panned all the way to the extreme L and R setting.
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Old 28th September 2011, 12:51 AM   #8
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The relative levels are critical as regards deciding what is going on, but 3.5mm stereo jack sockets (and plugs I guess), have an intrinsically high level of crosstalk, IIRC. You can probably find the figures on nwavguy's blog.
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Old 28th September 2011, 08:28 PM   #9
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Default Problem Solved

Thanks to everyone who responded!

The problem was that the sound card was set to Game Mode, so I disabled all sound blaster effects.

Cheers,
Jeff
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