Originally Posted by n38139
I've done most of what you asked, I will do the other pieces when I go back out to the hangar.
I have flown GMA 240 and GMA 245 audio panels for 11+ years, and they have always been super quiet.
We use the Bluetooth audio from the GMA 245 in 2 flight test aircraft on every flight to provide the same audio that the pilot hears to the Virb Ultra 30 camera. The flight video is so quiet between intercom and radio activity that until you hear the first audio, you wonder if it has recorded any audio on that flight.
After reading the above report, we tested a GMA 240 to see if we could come up with any elevated background noise scenarios. The only thing we came up with was to pull out the right knob (music volume adjust), turn the music volume all the way up with no music source connected, and turn music on with the dedicated music on/off button. It is doubtful that anyone would ever do this, but it was the only scenario we could come up with that would cause elevated background "white noise".
As many know, we are proponents of creating high audio signal to noise ratios such that the system never ends up significantly amplifying any noise that might be present on an audio input. This is done by using relatively high volumes at the alert, music, and radio audio source, which results in using very low volume settings and low amplification at the audio panel.