This features 2 SID voices and 3 digi voices combined into one 8-bit sample track played by the remaining SID voice at 7.8KHz. Low pass filter is applied to the sample track to remove the sample carrier frequency. Cut off is adjusted to match with the instruments played.
Sample playback is the newfangled \"variable slope and leave the DAC inputs dangling in the breeze.\"
The number of digi channels is pulled from various comment on the internet, but rummaging through the code it looks like it supports 4 channels, each with a individual 16-step volume setting.
The song is repeated with only the sample track enabled.