Antex Electronics SX-5e - Manual (Page 22)

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a file, but no fading. Some audio editing programs do edit MPEG
files, but they actually convert the file to PCM16 first, and then
convert it back again after editing. This has two problems. First,
it is slow, and second, each time the conversion is done, the
sound quality is degraded. MPEG is only valid for 32, 44.1 and 48
KHz. MPEG requires a great deal of DSP processing power. As
a result, the SX-36 can record a 32 KHz MPEG file and play an-
other 32 KHz file back at the same time, but not 44.1 or 48 KHz
MPEG files. The SX-34 or SX-36 can simultaneously record and
play back 48 KHz PCM16 files.
ADPCM is typically 4 to 1 compression, however, lower sample
rates are possible. Therefore, an ADPCM file recorded at 8 KHz
will use half the disk space of an MPEG file recorded at 32 KHz
with 8 to 1 compression. The sound quality will be much worse,
but if the application is to record a conversation for archive pur-
poses, the sound quality may be adequate. ADPCM is also easier
to edit.
In a network environment, where all sound files are stored on a
server and sent to the individual computers via a network, the
data rate is an issue of concern. If the network cannot send the
data from the file on the server to the computer fast enough, there
will be objectionable “dropouts” or “pops and clicks” in the audio.
Using a compressed file format will allow for more network traffic
before this problem occurs. Also, compressed file formats are
advantageous if the files must be sent by modem or emailed
somewhere.
ISO/MPEG-1 BITRATES
ISO/MPEG supports several compression bitrates. (The bitrates in
the Antex Demo program are selected by double-clicking on
MPEG in the Compression list to get a bitrate drop-down menu)
MPEG-1 has a range of compression ratios that are user select-
able. The compression ratio selected will depend upon the audio
quality required. The MPEG-1 format specifies the compression
ratio by defining the desired bitrate. The compression ratio ob-