True mute

[aentwistle]

Currently mute operates by setting volume to 0, which still leaves a hiss from the amplifier noise. I found that driving the ampliier enable pin as well, or instead provides a true mute, with no apparent ill effects. If people are happy I will do a pull request to implement this?

[max-arnold]

Hi!

I'm not against a PR, but it has to consider the following things (see the schematics):

1. There is the AMP_EN pin that controls NS4160 but doesn't affect the headphone output
2. There is the MUTE pin that provides a different way of muting both speaker and headphones, but I have no idea whether it fixes the hiss
3. There is a different receiver PCB version that adds a headphone amplifier circuit, see A new PCB with the headphone amplifier #42. I have no idea about the schematics and how to mute it correctly

If we are going to change the current muting implementation, it has to work correctly in all scenarios.

[max-arnold]

I guess we can ask @atsmini about the improved schematics with the headphone amplifier

[entwistlea]

I only propose driving the AMP_EN pin for the moment to silence the speaker output on mute, with no change to headphone output behaviour. It would be interesting to see the schematic of the headphone amplifier version.