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Surround Sound 7.1 Through 3.5mm Jack???

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StudentSA

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Hi,

I have these USB sound cards that I have been using and was wondering what the 7.1 meant, a quick googling and I found it it means it can drive 7 speakers.

SoundCard.jpg

My question is HOW?

It has a single 3.5mm audio out jack that to my knowledge only supports left and right channels?
 
The signal would have to be in digital format (S/PDIF) to support 7 channels through a 3.5mm audio jack.
Typically the digital signal is carried by an optical TOSLINK connector and cable but it can be carried over a coax line.
 
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I have used units exactly like this, and have used the optical output to my sound bars, and the sound is fantastic. 7 speaker...welllll no, but still surrond sound
 
The 3.5 jack is clearly used for headphones in your example. 7.1 can be "mixed down" to Left and Right
5.1 is left and right front and rear. the .1 is the subwoofer which is not full bandwidth. The other 2 to make the 7.1 is the delayed channels.

S/PDIF is very specific in terms of channel bit rate. 5.1/7.1 and PCM (Digital left right) are possible.
 
Those use the CM108 by C-media. Very nice little USB-audio (audio spec ver 1.0, USB ver 2.0) chip. It is strictly stereo 16-bit @ 48kHz441.kHz.

As with many USB soundcards, any mention of '5.1' or even 7.1' is emulated in software before the device gets the data. That is to say it attempts to reproduce the effect, without actually having 5/7 channels. How it does this is dubious because you cannot connect more than two speakers to it, even the S/PDIF output only supports stereo at the above sample rates. For true 5.1 S/PDIF it would require 16*48k*6 = 4.608MB/sec which is beyond the capability of a USB 2.0 'full speed' device, so such multichannel USB devices use high-speed.

With that said, these are so dirty cheap, and are handy for recording because all the analogue can be 'outside' the PC, and so with careful power-supply filtering/buffering it can get quite low noise. Even rivaling 24-bit 96kHz internal soundcards (which may well redcord in 24-32-bits, but often have a higher noise floor, making the extra resolution/sample-rate somewhat redundant).

TL:DR - Both input and output are stereo analogue, two-channel.
 
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