Antex electronic SX-33E, SX-33B user manual ISO/MPEG-1BITRATES & FORMAT EXTENSIONS

ISO/MPEG-1 BITRATES & FORMAT EXTENSIONS

ISO/MPEG supports several compression rates and encodes flags that describe the audio data. The flags and other options are selected by typing MPEG with[extensions] switches in the Format text box of the DOS demo. (The bitrates in the Windows demo are selected by double-clicking on MPEG in the Compression list to get a bitrate drop-down menu)

MPEG[extensions]"

where [extensions] is a concatenation (in any order) of:

/L =1 (layer 1) or =2 (layer 2),

/sr =32000 =44100 or

=48000 (to specify the sample rate),

/M =st (mode = stereo)

=js (mode = joint-stereo) or =dc (mode = dual channel) or =sc (mode = single channel)

/kB=Kbits per second per channel

/E =1 (crc error checking) or =0 (no crc error checking), /C=1 (copyright protected) or

=0 (not copyright protected), /O=1 (original) or

=0 (copy),

/Em =0 (no emphasis) or

=1 (emphasis 50/15ms) or =2 (reserved)

=3 (CCITT J17)

For example to get a 5.5:1 compression ratio, layer II and joint stereo in a 44.1kHz file:

1.Select 44100 from the SampleRate menu

2.Click on the text box lableled Format

3.Type MPEG/kb=128/m=js/l=2

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- tained for a given output bitrate therefore changes with sample rate.

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