This feature is used to convert Microsoft wave files (.wav) to 1-bit DPCM samples, as used by the NES hardware's sample channel.
The format of the wave files must be .wav PCM, no compressed audio formats are supported.
Sample rate, sample size and channel count doesn't matter, the file will be resampled according to the quality setting.

Choose import in the DPCM instrument editor dialog, select a file and you will be asked to select a quality and volume setting:

• Quality
  Sets the sample rate for the converted sample, this is equivalent to the pitch setting in the instrument editor. Use the same setting to play the sample at original pitch. Quality of 15 gives the best result at the cost of shortest sample time.
  
  
• Gain
  Sets the conversion volume level. Range: -12dB to +12dB.

Maximum supported size of one DPCM sample is 4 kB (4081 bytes).
At rate 15 (33.14394 kHz NTSC / 33.2521 kHz PAL), the play length is a little less than a second, while the lowest rate 0 (4.18171 kHz NTSC / 4.17740 kHz PAL) lasts about eight seconds.