I'm trying to simply record a sample and write it to a file.
Then read the file and play it.

My intention was then to add filters as the OP suggests to do 'voice changing' and etc.

However my patch runs fine on my Mac, but on Android the file write part just opens a file, then quickly dies. Its clearly seen on the emulator where a file 44 bytes is written then closed.

My guess is that Android can't write the file fast enough to cope with the input from the adc. With that in mind buffering may help, but it may limit the length of the sample.

Currently I"m just connecting the adc~ output to ~writesf with a suitable bang and parameterisation through a symbol to set the output filename.

I would otherwise use the Android libraries to record the sample, then just apply effects with PD, but the convenient MediaRecorder API only records compressed formats which PD cannot read.