Noise in additional audio inputs using the audio expansion capelet

Luca

Hello there! I'm having some trouble while using the audio inputs on bela's audio expansion capelet. While the native input on the board sound fine, the additional inputs (0-1-2-3-4-5-6-7) sound lower in volume and are pretty noisy, even without attaching cables they're output contains a low distorted hum and a high pitch, intermittent sound (similar to when you hold phones in front of an amplifier). How can I better their performance?

giuliomoro

This old blog post highlights the core difference between the audio inputs and the analog inputs on Bela: the audio inputs are designed for audio, the analog inputs are not. As such, forcing audio into the analog input technically works but it is expected to deliver lower quality than the audio inputs. In order to obtain better quality there are two tools at your disposal:

reduce the number of analog channels to 4 and thus increase their sampling rate to 44100
maximise signal-to-noise ratio by ensuring that the level of the analog signal going into the analog in is as close as possible to the clipping range. Install the gain jumpers if you need to boost your signal by 20dB before it gets converted.

Luca

Hi Giulio, thank you for the advise. One more question: if I reduce the number of analog channels to would that also translate to halving the number of inputs and outputs I have at my disposal?

Thanks again!

giuliomoro

Yes

Luca

Ok, thanks!