Comm on top of audio

[Oznog]

I am debating the best way to do this.
I am very limited on wires here, needing to do a stereo headset with microphone on a 3-pin jack. The system has a dsp processor in the headset and one interesting option is to send the digital data for the mike back to the central processor on a higher frequency, outside the audio range, that is too high a freq for the speaker to draw much current off of.

The audio is expected to be 128kbit/sec. I don't think I have resources available to compress it to a lower bandwidth. Any ideas if this could be transmitted this way, and what protocol or physical layer would work? I did note that since it's stereo there's 2 wires available to modulate it on, so differential transmission is an option.

Maybe it's a simpler option to just bump up the frequency of the mike signal and send it back in analog.... there are some reasons I don't feel too good about this option though.

 

[Paul Obrien]

The mini disc (c SONY) uses a DC shift in the remotes i.e. by varying a DC voltage different commands are executed.

 

[Pommie]

If you convert the 2 signals into constant currents and have a fixed resistance across the signal/ground line then each end can work out what current the other end is sending. This would give you 2 way communication over 1 line. I'm sure this must have been done before and someone more familiar with audio systems will be able to come up with something along these lines .

Mike.

 

[Oznog]

The low freq option is out for 2 reasons:
1. You can only transmit tiny amounts of data this way. More than a few bits per sec and the frequency of the signal goes into the audible range.
2. The low freq range is unavailable anyways because the DC component is already being used to power the logic inside the headset.

 

[Paul Obrien]

Is this a noise cancelling headset?

 

[Oznog]

Yep that's the idea.