參數(shù)資料
型號(hào)： MT9300B
廠商： Mitel Networks Corporation
英文描述： Multi-Channel Voice Echo Canceller(多通道話音回聲消除器)
中文描述： 多通道語(yǔ)音回聲消除器（多通道話音回聲消除器）
文件頁(yè)數(shù)： 7/37頁(yè)
文件大?。?/td> 179K
代理商： MT9300B
Advance Information
MT9300B
7
Figure 4 - Echo Canceller Functional Block Diagram
Linear/
μ
/A-Law
+
Non-Linear
Processor
Offset
Null
μ
/A-Law/
Linear
Linear/
μ
/A-Law
Microprocessor
Interface
Double-Talk
Detector
Disable Tone
Detector
A
F
C
Narrow-Band
Detector
μ
/A-Law/
Linear
Offset
Null
Echo Canceller (N), where 0
≤
N
≤
31
Sout
Rin
Sin
Rout
-
Programmable
Bypass
Disable Tone
Detector
(channel N)
(channel N)
(channel N)
(channel N)
GCI
PORT1
GCI
PORT2
12dB
Attenuator
MuteR
MuteS
Instability
Detector
Path Change
Detector
Adaptive Filter
The adaptive filter adapts to the echo path and
generates an estimate of the echo signal. This echo
estimate is then subtracted from Sin. For each group
of echo cancellers, the adaptive filter is a 1024 tap
FIR adaptive filter which is divided into two sections.
Each section contains 512 taps providing 64ms of
echo estimation. In
Normal configuration
, the first
section is dedicated to channel A and the second
section
to
channel
B.
configuration
,
both
sections
provide 128ms of echo estimation in channel A. In
Back-to Back configuration
, the first section is
used in the receive direction and the second section
is used in the transmit direction for the same
channel.
In
Extended
are
Delay
cascaded
to
Double-Talk Detector
Double-Talk is defined as those periods of time when
signal
energy
is
present
simultaneously. When this happens, it is necessary
to disable the filter adaptation to prevent divergence
of the Adaptive Filter coefficients. Note that when
double-talk is detected, the adaptation process is
halted but the echo canceller continues to cancel
echo using the previous converged echo profile.
in
both
directions
A double-talk condition exists whenever the relative
signal levels of Rin (Lrin) and Sin (Lsin) meet the
following condition:
Lsin > Lrin + 20log
10
(DTDT)
where DTDT is the Double-Talk Detection Threshold.
Lsin and Lrin are signal levels expressed in dBm0.
A different method is used when it is uncertain
whether Sin consists of a low level double-talk signal
or an echo return. During these periods, the
adaptation process is slowed down but it is not
halted.
In the G.168 standard, the echo return loss is
expected to be at least 6dB. This implies that the
Double-Talk Detector Threshold (DTDT) should be
set to 0.5 (-6dB). However, in order to get additional
guardband, the DTDT is set internally to 0.5625
(-5dB).
In some applications the return loss can be higher or
lower than 6dB. The MT9300B allows the user to
change
the
detection
application’s need. This threshold can be set by
writing the desired threshold value into the DTDT
register.
threshold
to
suit
each
The DTDT register is 16 bits wide. The register value
in hexadecimal can be calculated with the following
equation:
DTDT
(hex)
= hex(DTDT
(dec)
* 32768)
where 0 < DTDT
(dec)
< 1
Example:
For DTDT = 0.5625 (-5dB), the
hexadecimal value becomes
hex(
0.5625 * 32768
)
= 4800H
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