Introduction
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Introduct
ion
Packet Voice Processor Commands Manual
Full Rate (Rate 1) – 8.5 kbps or 171 bits/frame; transmitted/Received in 22
Byte increments and isused for carrying active speech
Half Rate (Rate 1/2) – 80 bits/frame; transmitted/Received in 10 Byte
increments and is used for carrying transition speech activity from active
speech to silence or noise or from silence or noise to active speech.
One Eighth Rate (Rate 1/8) – 16 bits/frame; transmitted/Received in 2 Byte
increments and is used for carrying silence or noise.
1.4.1.2.3 Discontinuous Transmission (DTX)
Discontinuous transmission or DTX is supported on this release. If DTX is not
enabled, then the EVRC CODEC supports only a single full rate mode. If DTX is
enabled, then silence suppression is enabled and the above three operating modes,
full, ½ and 1/8 rate modes are supported. With DTX enabled three additional
parameters are supported in the policy; dtxmax, dtxmin and hangover.
dtxmax: The dtxmax parameter indicates the maximum number of update
intervals in the number of frames for sending new silence frames. The
permissible values are from 0 to 255. With the dtxmax parameter set to 1 the
update interval is performed every 20 mS and if set to 255 the update
maximum interval is 5.1 seconds. If the dtxmax parameter is not present,
then thealgorithm assumes a default value of 32 only if silence suppression is
enabled.
dtxmin: The dtxmin parameter indicates the minimum DTX update interval in
number of frames. The permissible values are from 0 to 255. With the dtxmix
parameter set to 1 the update is performedevery 20 mS and if set to 255 the
update is performed every 5.1 seconds. If the dtxmin parameter is not
present, then the algorithm assumes a default value of 12 only if silence
suppression is enabled.
Hangover: The hangover parameter indicates the number of consecutive
silence frames transmitted at the end of an active speech interval but before
the DTX interval begins. The permissible values are from 0 to 255. With the
hangover parameter set to 1 the DTX interval begins on the next 20 mS frame
and if set to 255 the DTX interval begins in 5.1 seconds. Hangover value of
zero although allowed should not be used. Recommend setting hang over to
values greater than 1. If the hangover parameter is not present, then the
algorithm assumes a default value of 1 only if silence suppression is enabled.
1.4.1.2.4 silencesupp
The silence suppression parameter indicate if the sender is capable of sending and
receiving silence suppressed speech using DTX or does not want to receive silence
suppressed speech using DTX. A value of 1 indicates the sender is capable of
sending and receiving silence suppressed speech using DTX and will send out
silence suppresses speech using DTX. A value of 0 indicates the receiver does not
want to receive silence suppressed speech using DTX and will not send out
silence suppressed speech using DTX. If the silencesupp parameter is not present,
then the algorithm assumes silence suppressed speech using DTX is enabled.
1.4.1.2.5 AEC Support
Two AEC modes are supported; uncompressed for G.711 u or A Law to G.711 u or
A Law or G.711 u or A Law to EVRC0 and compressed for EVRC0 to EVRC0
transcoding. With EVRC0 to EVRC0 Acoustic echo cancellation is performed in the
compressed domain, without converting back and forth between the linear domains,
thus significantly reducing processing delay.
Содержание Packet Voice Processor
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