Sound Manager and "file reference numbers"

Hi all --

I'm running 5.6.1b3 on an iBook.  I'm trying to get a MacPerl script to 
play AIFF files, using the SndStartFilePlay function:

	use Mac::Sound;

	$sounddir = "Macintosh HD:Moreton:exp14:SW:testsounds";

	$infile = "$sounddir:000.aiff";
	open (IN, $infile) || die "Couldn't open $infile";

	$kBufferSize = 20000;

	$err = SndStartFilePlay (0, IN, 0, $kBufferSize, 0, 0, 0, 0);

	print "Error:  $err\n";


When I run this, I get the message:


	#Usage:  Mac::Sound::SndStartFilePlay(chan, fRefNum, resNum, 
bufferSize, theSelection, theCompletion=0, async==false).
	File 'Dev:Pseudo'; Line 10

There isn't any MacPerl documentation on SndStartFilePlay (not even in 
Sound.pm), but Inside Macintosh documents it for C (Sound Reference, 
Chapter 1, pp. 37f), and the only thing I can see that I might be doing 
wrong is that SndStartFilePlay might want the file to be identified with a 
"file reference number" rather than the filehandle I'm using right now.  
What is a "file reference number", and how do I set one up?  


Many thanks,
Elliott Moreton