Correct an error about burncd(8). To burn audio CDs with this latter raw

PCM files have to be used and not WAV files, I explained why and how
to convert the WAV files.

en_US.ISO8859-1/books/handbook/multimedia/chapter.sgml

@@ -705,9 +705,16 @@ MPEG 1.0 layer III, 128 kbit/s, 44100 Hz joint-stereo
       <para><application>XMMS</application> writes a file in the WAV
 	format, while <application>mpg123</application> converts the
 	MP3 into raw PCM audio data.  Both of these formats can be
-	used with <application>cdrecord</application> or
-	<application>burncd</application> to create audio
-	CDROMs.</para>
+	used with <application>cdrecord</application> to create audio CDs.
+	You have to use raw PCM with &man.burncd.8;.
+	If you use WAV files, you will notice a small tick sound at the
+	beginning of each track, this sound is the header of the WAV
+	file.  You can simply remove the header of a WAV file with the
+	utility <application>SoX</application> (it can be installed from
+	the <filename role="package">audio/sox</filename> port or
+	package):</para>
+
+      <screen>&prompt.user; <userinput>sox -t wav -r 44100 -s -w -c 2 <replaceable>track.wav track.raw</replaceable></userinput></screen>
 
       <para>Read <xref linkend="creating-cds"> for more information on using a
 	  CD burner in FreeBSD.</para>