The sampling frequency of the
traditional narrowband speech signals is 8 kHz, and the speech frequency ranges
from 200 Hz to 3400 Hz. With the development of communication technologies,
users have higher requirements for speech quality. The narrowband speech
signals, however, cannot always meet users' requirements for speech quality.
Wide Band Adaptive Multi Rate Codec (WB AMR) is introduced to provide
high-grade speech quality.
The sampling frequency of WB AMR is 16
kHz, and the speech frequency ranges from 50 Hz to 7 kHz. Compared with AMR, WB
AMR has wide high frequency extension and low frequency extension. Thus, WB AMR
can provide better speech quality.
In the GSM system, WB AMR specifies
five speech coding rates. In addition, WB AMR occupies only full-rate channels.
Currently, Huawei WB AMR supports only
one Active Codec Set (ACS). The ACS contains three speech coding rates: 6.60
kbit/s, 8.85 kbit/s, and 12.65 kbit/s. The BSC automatically selects an
appropriate speech coding rate from the ACS.