It is possible to import PCM wave files
and convert to 1-bit DPCM samples. The format of the
samples must be raw PCM, no compressed formats are supported. Sample rate,
sample size and channel count doesn't matter, the
file will be resampled according to the quality setting. However you might get
better results if you resample the file manually before importing it, sample
rates are described here.
Choose import in
the DPCM instruments dialog, select a file and a new dialog will come up where
you choose quality and volume:
Max size of one DPCM sample is 4 kB, at quality 15 (33 kHz) it's a little less than one second and lowest quality (4 kHz) about eight seconds.