I don't understand how the mono file input (bell.aif) can
output 4 channels of audio!
It doesn't... there are 4 output channels from the object but only the first shows a change in envelope when you play it. The rest output 0 as the file is only mono.
But I get the output in the 4 channels when I click the message "open ../sound/bell.aiff 0 200 4 2 b, 1", which is one of the messages from the help file. It also plays the file faster and at a higher pitch. Tested on Pd 0.52-4, macOS 10.14.6
Something seems funny (should I open an issue on github?), and the documentation may also be improved as to how those arguments work.
cheers