Bela_setAudioInputGain clarification

tsx

Hi,

I recently upgraded to v0.8h and the audio-in settings stopped working (custom stuff and using cross-compilation not the IDE). I saw giuliomoro's post about setADCLevel being deprecated and replaced it with setAudioInputGain and setAdcLevel but have got something that's not making sense:
- if I set the PGA gain (to e.g. 10) using setAudioInputGain and do not invoke setAdcLevel then it works ok
- if I set the PGA gain (to e.g. 10) using setAudioInputGain and set the ADC level (to e.g. 0) using setAdcLevel then I get nothing

Any suggestions as to why and any recommendations on how it should be?

Also - the bela.io doc says setAudioInputGain sets the PGA level and setAudioInputGain sets the ADC level but the comment in the header file says setAudioInputGain replaces setAdcLevel. Which one is correct?

Bela.h

40 // - removed setAdcLevel(): use setAudioInputGain() instead

giuliomoro

Is this using C++/PureData/Csound or using Supercollider? Supercollider has a bug that needs to be fixed and a workaround for which is explained here.

For the others (it seems you are using C++), I would recommend deleting the settings.json file from your project and refresh the IDE page so to start with fresh settings. Then you should be able to use the settings in the IDE to set the input gain. What happens in the backend is that for positive gain values, the ADC attenuator is set to 0dB (no attenuation) and the PGA is set to the positive value. For negative gain values, the PGA is set to 0dB and the ADC attenuator is used to achieve a value (close to) the specified one.

tsx - if I set the PGA gain (to e.g. 10) using setAudioInputGain and do not invoke setAdcLevel then it works ok

this looks good, assuming you mean Bela_setAudioInputGain().

tsx - if I set the PGA gain (to e.g. 10) using setAudioInputGain and set the ADC level (to e.g. 0) using setAdcLevel then I get nothing

Whichever of Bela_setAudioInputGain() or Bela_setADCLevel() gets called last is what ultimately sets the input gain, so it may be that with a gain of 0 you don't actually much input level at all .. anyhow you should not need to call Bela_setADCLevel() in any case going forward because of what I explained above.

tsx

Thanks @giuliomoro!

It's using straight C++ and calling Bela_setInputGain works fine. But been plodding though the core source to see what was happening under the hood. It looks like when Bela_setAdcLevel calls the codec setInputGain it also sets the PGA gain so invoking Bela_setAdcLevel with a dB > 0 seemed to work too.

I'd previously had it configured so that the ADC wasn't running at max and the PGA was adjusted to get the level I wanted but it doesn't seem like that's really necessary.

RTAudio.cpp

// Set the level of the ADC
// 0dB is the maximum, -12dB is the minimum; 1.5dB steps
int Bela_setADCLevel(float decibels)
{
return Bela_setAdcLevel(-1, decibels);
}

int Bela_setAdcLevel(int channel, float decibels)
{
if(gAudioCodec == 0)
return -1;
return gAudioCodec->setInputGain(channel, decibels);
}

giuliomoro

tsx I'd previously had it configured so that the ADC wasn't running at max and the PGA was adjusted to get the level I wanted but it doesn't seem like that's really necessary.

Yes that was the reason why we removed that setting: it wouldn't make sense to attenuate the ADC just to boost the gain of the signal before it hit the ADC. It was exposed for legacy reasons but it was not really meaningful to use them both at once.

tsx

Makes sense I guess, since boosting the input signal also boosts the noise. And thanks for the help :-)