Hello, I had some time tonight to test out the audio expander caplet tonight. I'm just doing a in to out configuration. That is do an analog read and then an analog write. So it should (in theory) just pass the signal through / reproduce it. The good news is that input to output (when running a frame size of 2 samples) was something like 4 samples. So the latency is very good. I verified this by using an independent computer sampling the input and the output.

However, I'm wondering about some things though. Issue #1. It seems I have to multiply the input by 10 to get a line level output, even though I'm feeding a line level signal into the Bela. I'm not using the jumpers because the signal is a line level signal. This seems odd. I added in the jumper and nothing changed. Hmmm.

Issue #2. It seems theres some wild stuff going on with the signal. It starts off with the -1 at 0 and slowly swoops down to center on the 0. Also the tops of the square wave are always tilted. So I guess I don't have the right words to describe it, but it seems to not reproduce the input signal very well. I've attached a screenshot here. The middle Signal is the square fed back into the computer, and the bottom signal is the signal that goes through the bela.

alt text

Okay, I think I figured out the audio quality thing. The jumper actually needs to be in the opposite location I thought it did. Whoops. However the bad thing is that now there's latency (something like 30 samples). Hmmm.

alt text

alt text

Doh. Somehow the project settings all reverted (including the 16 frame size). So now setting back to 2 samples frame size, and having the jumper in the right place I'm now getting something like 6 samples end-to-end latency. Which at 44100 is like 0.13 ms !!! So yeah - the audio caplet does work and the latency is amazing!

alt text

What you're seeing with the signal starting at 1 and going back to 0, and also with the tops of the square waves, are both effects of the high-pass filter (AC coupling) on the audio expander capelet. They're both totally normal effects, and you will see something similar with wave shapes on most audio interfaces at low frequencies.

Ok I updated the image in the wiki, hopefully now it is more clear

audio expander jumpers image