The U-1496 series modems support five voice digitization schemes. Four schemes use the ADPCM algorithm and one uses the advanced CELP (Code Excited Linear Prediction) algorithm to achieve near-phone-quality voice at 9.6 kbps speech data rate. A summary of these four schemes is listed below:
Digitization Speech Compression Data Rate Scheme Algorithm CELP Code Excited Linear Prediction 9600 bps 2-ADPCM ADPCM, 2 bits/sample 19200 bps 3-ADPCM ADPCM, 3 bits/sample 28800 bps 3-ADPCM(NEW) ADPCM. 3 bits/sample 30720 bps 4-ADPCM ADPCM, 4 bits/sample 38400 bpswhere the sampling rate used is 9600 samples per second.
The ADPCM voice modes are supported on all U-1496 series modems. However, the advanced CELP scheme is supported only on the plus version and the U-1496 LCD model.
Silence detection is implemented to eliminate voice data coding in silence period.
The modem also supports simultaneous DTMF (Dual Tone Multiple Frequency) tone detection that allows a user to use the keypad of a tone-dialing, push-button telephone set to control, instruct, or answer the modem.
Automatic detection of voice, fax, and data.
ZyXEL Advanced Voice Capability.