USB DAC to line in of and output of sound card?

[DangerClose]

Can a USB DAC be connected to a sound card's line in on the same computer?  To use the USB DAC but the amplifier and processing on the sound card.
 
I don't think it's possible since Windows would have to allow two audio outputs.

 

[MindsMirror]

That signal chain would look like this:
USB DAC > Sound card ADC > Sound card processing > Sound card DAC > Sound card amp > Headphones.
 
Technically you are using the USB DAC, but you wouldn't want to do that. The unnecessary steps involving the USB DAC and ADC do nothing but degrade the sound quality.

 

[DangerClose]

I was hoping the sound card line in could bypass its DAC.  

 

[ProtegeManiac]

  Can a USB DAC be connected to a sound card's line in on the same computer?  To use the USB DAC but the amplifier and processing on the sound card.
 
I don't think it's possible since Windows would have to allow two audio outputs.

 

Even if it could do that you won't be able to use all the DSP features on the soundcard. Like virtual surround. You can't have that work with a signal that, as far as the DSP chip was concerned, was originally analog stereo. When you want virtual surround your game's audio needs to be set to surround and then it's the DSP that figures out how to downmix it into a 2ch signal that can give you positional cues.

 

And what for? You assume the DAC will be better, but then you run it through the soundcard's ADC, then through its DSP, then through the soundcard's DAC, so in the end you'll still use the soundcard's DAC. Even if it appreciably sucks by comparison, the thing is you just ran the signal that not only came out of the perceived (not necessarily actually) better DAC and analogue output stage on the DAC, then run it through the soundcard.

 

If you want to utilize DSP features but then use a better DAC and amp circuit then just use the SPDIF output of the soundcard to feed an external DAC+HPamp with SPDIF input.

 

[DangerClose]

It's not about using the DSP.  It's about using the sound card's amp because the external DAC doesn't have one.  

 

[ProtegeManiac]

  It's not about using the DSP.  It's about using the sound card's amp because the external DAC doesn't have one.  

 
Then why not just get an external amp to go with the external DAC rather than run the signal through a DAC then through an ADC again just to run it through the amp? And chances are the input is probably a mic input, which might only work in mono, unless it's a soundcard designed for recording.

 

[DangerClose]

   
Then why not just get an external amp to go with the external DAC rather than run the signal through a DAC then through an ADC again just to run it through the amp? 

 
I realize my first post may have caused confusion by saying "processing," but it's not about using the DSP, and I was hoping the line-in could bypass the sound card's DAC.
 
What I thought would be the greater problem is using a USB DAC on the same computer -- getting Windows to allow a USB DAC output at the same time as a sound card output.
 
It'd be nice to use the sound card amp because the sound card amp already exists.

 

[ProtegeManiac]

   
I realize my first post may have caused confusion by saying "processing," but it's not about using the DSP, and I was hoping the line-in could bypass the sound card's DAC.

 

What I'm saying is that any input into a soundcard is assumed by the manufactuer to be intended to be digitized to begin with, whether it's a recording input or a mic input for gaming comms (ie the audio goes through the internet, not a shortwave or satellite radio), so any analogue input into a soundcard will inevitably run through its ADC, DSP, and then a DAC somewhere, whether that DAC is on some other computer whose user is screaming "Rush B! CYKA BLYAT!!!" or your own computer.

 

Again - the analogue inputs on sound cards are typically not directly connected to its own analogue output circuits.
 

 
It'd be nice to use the sound card amp because the sound card amp already exists.

 

Unfortunately it works the same way that an RCA input marked "Phono" on most home theater receivers work, so even if you somehow get the soundcard to run that way, it will still do the DAC-ADC-DAC loop.

 

[Roseval]

Maybe this link is of use: http://www.hardwaresecrets.com/how-on-board-audio-works/3/
It confirms what ProtogeManiac says, all analog input is digitized and converted back to analog by the soundcard.
Even if you get it to work (USB audio out + soundcard out, maybe Virtual Audio Cable can do that) you are still using the DAC of the soundcard.
As this is the case you might as well skip the USB part entirely or get yourself a USB DAC with a decent headphone out.