On my device, OpenSL ES (Android’s low-level sound API) seems to have issues. I’ve tried using SunVox (paid app, sorry, but it’s worth it if you’re interested in making music) and get all sorts of pops and crackling, even when disabling visualizations (logo on the top left, Preferences, Modules, disable “Show oscilloscope” and “Show level meter”) or increasing sample buffer (in Preferences, Audio, set Buffer to a high value). Sounds to me as if the audio samples don’t get to the DAC fast enough or there’s too little buffer somewhere else down the line. Caustic (free demo) works when using the