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Edit: So even read the diagram, drawn and added the pictures. The part is a low impedance voltage divider capacitors before! Component value a maximum of 5 euros ...
At the final stage mass of audio signals is usually associated with body mass, ie you can connect the "-" actually save complete terminal since the audio signal is usually derived directly to ground anyway ...
The circuit for generating the remote signal is a bit more sophisticated - here you have even installed a hysteresis. To push the audio signal through a diode and then to hunt directly into a buffer capacitor (!) Is rather ugly.
With good sound quality, this circuit has something to do little.
