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Cheap way to mix two digital audio signals together and output digitally?

Robonaut

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Okay, here's the situation. When I'm playing video games on my PC, I often like to listen to my music collection or podcasts instead of the game's music. But I still want to hear the game's sound effects, dialogue, etc.

So, what I would like to do is take a coaxial digital audio output from my computer, a coaxial digital audio output from my digital audio player, combine them together with the ability to adjust the relative levels (that part is key!), and then output a new digital coaxial audio output to feed to my DAC.

I would have thought that modern DJ mixers would be able to do this, but the only one I've been able to find that seems to be able to mix digital signals and output them digitally is a $2K Pioneer unit (https://www.sweetwater.com/store/de...j-djm-900nxs2-4-channel-dj-mixer-with-effects), which is *way* more than I want to spend on this.

Any ideas on how to do this cheaply?
 

Helicopter

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I wonder if the audio interfaces with digital inputs and outputs do this.

Why not combine the signals in your computer OS and then go digitally to DAC, like get a Focusrite Scarlet 8i6 or Motu ultralite and use the digital input for the music, then play that audio and game audio in your PC, output it through the interface digital output and then go to the DAC.
 

DVDdoug

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There's probably just not enough demand to make something like that popular and cheap... And even if mass-produced and mass-marketed it would be more costly to build than an analog mixer which is cheap & easy to make with an op-amp.

Also, the clocks wouldn't stay perfectly in-sync so you'd loose or gain a sample here-and-there although that probably wouldn't sound terrible. If the sample rates and bit-depths are different one would have to be re-sampled... Not a BIG deal... Your computer does that every day but in-practice it's not as easy as analog mixing. "Coax" (S/PDIF) sometimes carries Dolby AC3 or DTS which would have to be decoded before mixing.
 

sergeauckland

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Pro digital mixers have a sample-rate converter/synchroniser on every input, converting to whatever the mixer's internal sample rate and/or output sample rate is. This ensures that whatever the incoming signal, with whatever clock rate and drift, the streams stay synchronised. The alternative, much less convenient, is to have a master clock system which locks all the sources to the one clock. OK if all the sources are in the studio, but of no use if any of the sources are generated externally.

As DVDdoug posted above, there's probably not enough requirement for a simple and cheap product. All proper digital mixers I'm aware of are indeed in the thousands.

S
 
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