Lower cut-off for DC-filter in Bela Gem firmware?

RobinKoek

Hi all,

for a project which involves infrasonics I would like to use the Bela Gem Stereo to synthesise sinusoids all the way down to frequencies of 0.5 Hz driving a large diaphragm single speaker through a matched amp. I did a few tests and from 10Hz I could a observe steep sloping / filtering and with almost no response at 5 Hz. I assume this is the built-in DC filter and was wondering if it is possible to adjust the firmware, or perhaps a boot line of code which allows for full-range infrasonics up to ₀.01 Hz? Ideally it would be great to test with a lower cut-off frequency, while also being able to adapt the steepness of the filter, which seems set to 24dB per octave currently?

Thanks for advice!

Robin

giuliomoro

If you are using the headphones output (the jack socket), you'll have an analog high-pass on there:

You should use the line outs (available on a dedicated 5x1 header) which are DC-coupled. Note there is no protection at all on those, so maybe add a series 220R resistors if possible, to minimise risks of ESD damage, or something more sophisticated, depending on what you connect to it.

RobinKoek

Thanks for the swift and concise reply Giulio, this was the guidance we needed to adjust the filtering.

Kind regards