RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
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minimum on-time is inserted in the speech detector to smooth the switching effect over weak sounds, especially for
consonants at the end of a word or sound level very close to the noise floor. Note that the switching here is totally different
from that in half-duplex speakerphones where the voice channel is gated. In the FDX Speakerphone Mode, the voice
channel gain is always maintained except the AGC. Transmit speech hangover (address 479h in single bank memory) and
receive speech hangover (address 488h in single bank memory) values can be optimized to each specific language. The
default values are optimized for American English.
Minimum On Time (ms) = Speech_hangover / 8.
When the local speech is detected, the transmit speech active bit (1E:7) is set to a 1. When the far-end speech is detected,
the receive speech active bit (1E:6) is set to a 1. Each bit is reset to a 0, respectively, when speech is not present.
12.3.10 Scaling of Transmit Output to Line
The transmit voice (processed microphone signal) can be scaled to a desired level before sent to the line (refer to item 80 in
Table 4-1). The scalar defaults to maximum 7FFFh, making no attenuation on the signal.
12.3.11 Speakerphone Modes and Active Bits
The active bits in different speakerphone modes are listed in Table 12-1 and Table 12-2.
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