On the project I am working on, I have 3 line-level audio signals, and I need to determine on an arduino if a non-silent signal exists on each line and act appropriately (in my case, "unplugging" a device from mains voltage). My first over-engineered idea is to amplify each signal, add a dc bias, then do some expensive operations on the arduino to determine if an audio signal exists.
Each audio signal is a mono signal consisting of a ground wire and an AC, low voltage, audio wire.
Now I don't remember much from my analog class from university, but my gut instinct is this can be simply done using analog componenets where I can feed the result (an psuedo digital signal where high would be above voltage x and low would be below voltage y) and do much easier computation on the microcontroller to determine if a signal exists.
The frequency of the audio signal is between 10 to 22,000 Hz The peak to peak voltage (of the consumer level line level) is 894mV, but the circuit should be able to handle as low as 10mV peak to peak