I hadn't made the connection before, but this is basically how many industrial sensors work. They transmit currents of 4 to 20 mA, with 0 mA likely indicating power loss or a short.
The goal is essentially the same: make it easier to tell if the line's gone dead or not. I think it would be interesting if there could be a good use for comfort noise in these signals, too; at least for me, I've watched for noise levels to shift to figure out if something was amiss.
The goal is essentially the same: make it easier to tell if the line's gone dead or not. I think it would be interesting if there could be a good use for comfort noise in these signals, too; at least for me, I've watched for noise levels to shift to figure out if something was amiss.