Telos ZephyrExpress - Manual (Page 89)

CODING 5-11
CHOOSING THE CODING METHOD FOR YOUR APPLICATION
This chart describes and compares some of the important characteristics of each
method. Because ZephyrExpress includes all three popular coding methods, it’s possible
to choose the most appropriate one for each application.
Audio Coding Comparison Chart
Layer 3 Layer 2 G.722
Algorithm Perceptual+Huffman Perceptual ADPCM
Audio Freq. Response/mono 7 kHz
24 kHz sample rate, 64 kbps line 15 kHz 8.6 kHz*
32 kHz sample rate, 56 kbps line 15 kHz 7.8 kHz*
48 kHz sample rate, 64 kbps line 20 kHz 9.8 kHz*
48 kHz s/r, 128 kbps line** 20 kHz
Audio Freq. Response/stereo 7 kHZ
at 32 kHz sample rate 15 kHz
at 48 kHz sample rate 20 kHz 20 kHz
Delay at HALF/24 kHz 45 ms
Delay at 32 kHz/mono 275 ms 45 ms-
Delay at 32 kHz/dual mono 275 ms 45 ms-
Delay at 48 kHz/mono 225 ms 160 ms 45 ms-
Delay at 48 kHz/dual mono 225 ms 160 ms 45 ms-
Delay at 48 kHz/mono-128 220 ms
Delay at 32 kHz/stereo/jstereo 390 ms 45 ms-
Delay at 48 kHz/stereo/jstereo 270 ms 220 ms 45 ms-
Joint Stereo MS Matrix Intensity Coding
ISO Target Bit Rate 64kbps/channel 128kbps/channel N/A
Coding Power as In/Out Ratio 12:1 6-8:1*** 4:1
Frequency Bands 576 32 2
Frequency Resolution (48 kHz) 42 Hz 750 Hz --
* Layer 2 was not designed for the low bitrates of a single ISDN channel,
so the response is deliberately limited in some Layer 2 conditions
to reduce unpleasant high-frequency artifacts.
** Requires two 64kbps ISDN channels.
*** 12:1 in Intensity Joint Stereo mode
-G.722 delay will vary. Spec is 35 ms +/- 10 msec for 45 ms maximum
Delay times may vary depending upon ISDN line delay and other factors.
Frequency response is given for swept sine test; response with program material
may vary owing to the dynamic nature of the coding process.