By popular demand, I’ve now added a DMR mic gain control into the OpenGD77 firmware
The gain control only works for DMR as the signal path is different for DMR and FM. In FM the mic is connected directly into the input of the AT1846S RF chip, however in DMR mode the mic is connected to the analogue input of the HR-C6000 DMR DSP chip, which digitises the audio.
The HR-C6000 has an input gain control on the analogue input in 3dB steps, with the default value actually being 33db (or 11 as a direct value). In the OpenGD77 firmware the default value is displayed as 0dB, and adjustments can be made to increase or decrease from this value in 3dB steps, e.g. +3dB, +6dB, -3dB, -9dB etc
Additionally I’ve added a mic level monitor bar graph during Tx, which is displayed in the same position as the Rx signal meter bar graph.
This is only intended as a general guide to the mic level, which I created by sampling the mic audio for 100mS and recording the peak waveform level over that period.
I then take the square root of that peak level, and scale the value to match the width of the screen in pixels.
I think technically, the ideal method to monitor the level is to take the sum of the square of every sample than divide that by the number of samples and then take the square root of that value; however that would be a huge and unnecessary load on the CPU, and my more simplistic approach seems to give usable results.
This feature is available in the Tier2 Latest version of the firmware.