Page 24
Alcorn McBride MP3 Audio Machine User’s Manual • Rev H • April 2, 2004
& /
Play Lists provide a mechanism for the MP3 Audio Machine to automatically play a
collection of tracks in a predefined sequence. Play Lists often allow the MP3 Audio
Machine to be used to perform complex functions that would normally require an
external controller. Play Lists can perform functions as simple as looping a single
track, or as complex as user prompted pacing of the playback.
Overview
Play Lists hold the key
to the power of the MP3
Audio Machine.
A Play List file contains a list of numbers, which refer to audio tracks (or other Play
Lists) on the media in the MP3 Audio Machine. When a Play List is being used, the
tracks are played back in the order in which they appear in the list. The Play List is
an ASCII text file and can be made using any ASCII text editor (like notepad or DOS
edit). The maximum Play List file size is 64 KBytes (or about 16,000 tracks, if no
comments are used).
A Play List can be started by serial or parallel commands, in exactly the same way as
an audio track. For example, the serial message
2SE<CR>PL<CR>
causes Play List PLY00002.LST on the currently selected drive to start. Discrete File
Select Input 2 will also start PLY00002.LST.
If Play List 0 (PLY00000.LST ) exists, it will be automatically executed on power
up.
If a Play List contains the number of another Play List, execution of the first Play List
will be terminated at that point, and the new Play List will begin.
Segmented vs. Unsegmented Playlisting
The MP3 Audio Machine can play a variety of file types, as you can see in the
Supported Audio Types section. As the product transitions from one type to another
(MP3 to WAV, WAV to MP3) you may hear a slight pop in the speaker and line
level outs. This is due to the way the music is routed in the product. There is also
present, a very slight delay, as the program sets itself up for .WAV files recorded at
different frequencies (32, 44.1, or 48KHz). For this reason, playlisting can be split
up into two categories:
Segmented
and
Seamless (Unsegmented)
. The unit is smart
enough to dynamically transition between all the different file types it plays without
external intervention, like a playlist or serial command. While playlisting, if the unit
transitions from MP3 to another MP3, or 44.1KHz WAV to another 44.1KHz WAV,
the transition is
seamless
, with no delay or noise. While playlisting, if the unit
transitions from MP3 to WAV or vice versa, the transition is
segmented
, and the unit
has to reset its internal parameters to get ready for this next file type. The long and
short of this is that in order to make a seamless playlist, encode all your files as
MP3’s, or make them all the same sample frequency for the .WAVs.
