New parameter for de-emphasis selection

[Rfromearth]

I didn't test if the following propostion leads to a significant better sound for non us-people but in ats-mini.ino the de-emphasis for fm-radio reception ist set to 75µs per rx.setFMDeEmphasis(1). It would be nice to have this value selectable as another parameter to switch between 50µs (rx.setFMDeEmphasis(2)) and 75µs.

[li20034]

I have made a quick & dirty PR (#116) for this exact thing. Though, from what I can see in the datasheet, 1 is 50uS and 2 is 75uS. So the issue is actually, currently, the sound is too bright in US regions.

If anyone wants to test the sound difference, build artifacts are available on the branch in the PR. From what I can hear, the difference is faint, but just enough to be noticeable using headphones in a quiet environment.

[max-arnold]

Anyone tried the similar option for AM? Is it regional as well? Is the difference noticeable?

[Rfromearth]

Thank you for implementing my suggestion. And no, the idea of pre-emphasis/de-emphasis is only used for FM and PM (phase modulation) transmissions. Using this technique increases the SNR for the higher frequency components of the signal to be transmitted.

p.s.: Yes, the sound is noticeable better (here in Germany). Connected to an external amplifier I can hear the higher parts of the spectrum which where missing before. It's as if someone had taken the speaker(s) out of a box.
Perfect!