Synchronizing Analog and Audio Inputs?

freddyliu

Hello!

I am currently trying to use a Bela board with the Audio Expander Caplet to capture 10 channels of audio inputs (8 analog inputs and 2 audio inputs). Is there any recommended way I should sync these recordings, since the analog inputs are sampled at 22050Hz and audio inputs are sampled at 44100Hz, and there's a larger latency with the audio inputs compared to the analog? To tackle the sampling rate difference I was originally thinking of just reading 1 out of every 2 values provided by the audio inputs. For the latency I was going to just find the fixed delay difference and then shift the signals accordingly. However, from reading this website it seems there's a 'flag selectable at runtime in the Bela code' to align the audio and analog signals. Where would I be able to find this? Thanks very much for the help!

giuliomoro

We never implemented that flag, though we likely will in the next two months, for the release of the new generation of boards. So, a delay line is your best bet. Note that each analog input is sampled at a different time, unlike the audio inputs that are all samples at the same time. This means that you will always have sub-sample phase differences between the analog channels. If your application is sensitive to this type of phase inconsistencies, then the analog inputs may not be the right choice.

freddyliu

I see, thanks for the response! Is there a way to lower the audio sample rate to match the analog sample rates or would the above sampling strategy be fine?

giuliomoro

Not at the moment: the relationship between the sampling rate of the audio and analog when running with 8 analog channels is fixed to 2 : 1.

To tackle the sampling rate difference I was originally thinking of just reading 1 out of every 2 values provided by the audio inputs

This is the easiest "right" way of doing it.