Australian Monitor DMA1 - Manual (Page 4)

I N T R O D U C T I O N
PA G E 4 A M I S - D M A 1 I N S TA L L AT I O N & O P E R AT I O N M A N U A L
1.1 Introduction
The Australian Monitor Installation Series DMA-1 digital message
announcer is a compact yet highly featured digital playback device. Utilizing
an SD card digital storage format the DMA1 delivers high quality stereo
audio in an MP3 format. Messages can be played or triggered using the
on-board controls, via remote switches, contact closure or via RS485 serial
control. The DMA-1 also boasts an on board 20 watt per channel D class
power amplifi er as well as stereo inputs & outputs which allow it to be
inserted in line with another BGM feed.
The DMA-1’s compact size belies the wealth of features it offers. It is a
highly innovative & cost effective digital message storage & playback
device that has a host of commercial applications.
1.2 What is MP3?
MP3 is an acronym for Mpeg-1 layer 3. This is an audio compression
standard which eliminates sounds which the human ear cannot hear via a
psycho-acoustic algorithm. The purpose of this compression is to reduce the
space taken up by an audio fi le while still ensuring excellent quality. The
greater the compression, the less the audio quality. The right compromise,
which guarantees a quality comparable to that of a Compact Disc, is 128
Kbps (thousands of bits per second) which represents the most widely used
manner, and reduces the size of an uncompressed fi le by 10 times.
1.3 Encoder
Software which compresses a CD audio or wave fi le in MP3. There are
many programmes of this kind, and it is virtually impossible to say which is
the best. Freeware software encoders suitable for various
operating systems can be downloaded from the following internet site:
www.mp3server.4t.com
1.4 Decoder
Software which decompresses an MP3 audio fi le in order to send it to
a digital-analog converter and reconstruct the original audio signal.
1.5 Player
Hardware and software system able to read MP3 audio fi les. The DMA1
is able to carry out this function.
1.6 Wave
High quality audio format (extension .wav), compatible with the tracks of
normal music CD’s. CD quality music utilises a sample rate of 44.1 KHz/sec.
at 16 bit in stereo, but the size of the fi le is approximately about 10Mb per
minute.
1.7 Audio compression in various formats
The following graphic shows the space taken up by an uncompressed audio
fi le of about 5 minutes (.wav) and compressed in MP3 at 128Kbps (MP3).
WAVE 51.1MB
MP3 4.6MB