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D6571E Datasheet PDF : 117 Pages
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D6571E Data Sheet
Full Duplex SpeakerPhone Operation
In this mode the D6571E implements a HOST controlled
Digital SpeakerPhone algorithm. When activated, this
algorithm enables enhanced SpeakerPhone operation
with both Acoustical and Electrical Echo Cancellation
and programmable parameters. CODEC0 is used for the
telephone line input and output. CODEC1 is used for
the microphone input and the speaker output. (This is
the default setting of the Codec).
The SpeakerPhone command is comprised of two
commands. The first command defines the “static”
parameters, which usually are optimized to the specific
hardware setup (microphone and speaker locations,
amplifier gains, etc.). This command can be issued once
only while in SpeakerPhone mode. The second
command will define the “soft” parameters that can be
changed by the HOST during SpeakerPhone operation
(loop attenuation, speaker volume, etc.). The second
command can also define echo cancellation and loop
adjustment modes as well as instruct the D6571E to
generate a tone from the predefined table.
SpeakerPhone function has the same performance in
case of “cold” and “warm” start.
Explanation of the SpeakerPhone Parameters
Static Parameters (First Command)
R/T ratio (bits 11-10) and T/R ratio (bits 9 -8)
This is ratio of transmit and receive signals. This ratio is
used to determine which side is speaking. If the T/R
ratio is greater than the set level, this is an indication
that the microphone side is speaking. Conversely, if the
R/T ratio is greater than the set level, this is an
indication that the lin e side is speaking.
Priority (bit 1)
The system has two ways of behaving when neither
side is speaking. If this parameter is set to “0” - (no
Priority), the attenuation will be equally split between
two sides. If, for example, the total loop attenuation is
16 dB, when one side is active, the other side is
attenuated by 16 dB. If no one is speaking, both sides
will be attenuated by 8 dB. If the parameter is “1” -
(Near Side Priority), the telephone line side will be
attenuated (by 16 dB) and the microphone side will be
open (0 dB) when neither side is speaking.
VOX Sensitivity
The line and microphone sensitivity determine the
Signal-to-Noise (SNR) ratio at which the voice detectors
for the transmit and receive directions will be activated.
The voice detectors are used to determine which
direction is talking.
Line VOX Sensitivity (bits 7 -5)
This parameter will control the sensitivity of the VOX
from the line side.
Mic VOX Sensitivity (bits 4-2)
Same as above for the microphone input.
“Soft” Parameters (Second Command and
On)
Mode = 0000 (SpeakerPhone Status)
In this mode, the D6571E reports to the HOST the
current SpeakerPhone status.
Loop Attenuation (bits 2 -0)
This indicates the actual amount of loop attenuation
currently in use. See the Command Set description for
possible values of this parameter.
Direction (bits 7-4)
This indicates which direction (microphone/speaker) is
considered active by the D6571E SpeakerPhone control
logic. This is a 4-bit field used to represent the number
range from +7 to -8. The most positive values indicate
that the signal coming from the microphone is dominate
(microphone is speaking). The most negative values
(2’s complement) indicate that the signal coming from
the line side is dominant (telephone line is speaking).
Values in the center range can either indicate a
transition form one side to the other, or if the value
stays at approximately the zero position, that neither
side is talking. See the Command Set description for
possible values of this parameter.
Mode = 0001 (Line Status)
The D6571E monitors in this mode the telephone line
and reports the result of the CAS detection. The status
is updated by the D6571E every 16.5 msec. The D6571E
allows to send any other SpeakerPhone command and
receive status accordingly without interrupting CAS
detection (other SpeakerPhone commands have much
shorter response time). When set NEW STATUS bit
DS6571E.2
DSP GROUP, INC., 3120 SCOTT BOULEVARD
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SANTA CLARA, CA 95054 PH: 408 986-4300 FAX: 408 986-4490
 

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