mt90502ag2 Zarlink Semiconductor, mt90502ag2 Datasheet - Page 97

• Manufacturer Part Number: mt90502ag2
• Description: Multi-channel Aal2 Sar
• Manufacturer: Zarlink Semiconductor

2.9.4
When a PCM or ADPCM CPS-Packet is composed entirely of silent bytes, then it is tagged as being a silent
CPS-Packet. It is then sent off to the CPS-Packet Final Assembly Structure to be treated. A silent CPS-Packet will
not necessarily be discarded: the Final Assembly Structure contains 2 fields, the Voice to Silence Timer and the
Silence to Voice Timer, which indicate how long a channel must be silent before it starts being suppressed, and
how long a channel must be active before it starts being transmitted again. Usually, the Silence to Voice Timer is
close to 0, so that voice is never cut off at the beginning of a talk spurt. However, the Voice to Silence Timer can
be much longer, because it is not as important to start suppressing silence as soon as voice trails off: leaving a
certain silent time makes the transition to silence suppression much smoother. Note that both Timers are defined in
CPS-Packets, which is the most precision possible in this application.
To improve the Silence to Voice transition, another field called the TX Delay adds a constant delay of 0 to 4
CPS-Packets to the transmission: in other words, when the system must transmit a new CPS-Packet, it will transmit
the one from 2 CPS-Packets ago. Thus, by using a Silence to Voice Timer of 2 CPS-Packets and a TX Delay of 2
CPS-Packets, the Silence to Voice transition will have zero loss, while ensuring that small spikes of noise do not
cause the system to believe that continuous voice is being transmitted.
Voice/Silence Timer
Buffer[30]
Buffer[30]
Buffer[30]
Buffer[0]
Buffer[0]
Buffer[0]
...
...
...
...
Figure 60 - 32 SDRAM Silence Buffers
Zarlink Semiconductor Inc.
MT90502
Buffer[31]
Buffer[31]
Buffer[31]
Buffer [1]
Buffer [1]
Buffer[1]
97
...
...
...
...
Byte [size - 1]
Byte[0]
Byte[1]
...
Data Sheet