CS6422-ISZ Cirrus Logic Inc, CS6422-ISZ Datasheet - Page 37

• Manufacturer Part Number: CS6422-ISZ
• Description: IC CODEC SPKRPHONE 2CH 20-SOIC
• Manufacturer: Cirrus Logic Inc
• Type: Audio Processorr

Specifications of CS6422-ISZ

• Package / Case: 20-SOIC
• Applications: Speakerphones
• Mounting Type: Surface Mount
• Operating Supply Voltage: 5 V
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 598-1202-5

Suppression may cause some modulation of the
perceived background noise which may be distract-
ing to some users. As a result, it may be desirable
to limit the suppression attenuation to the minimum
necessary. The CS6422 provides TSAtt (Register
3, bits 15 and 14) to control the amount of attenua-
tion introduced by suppression in the transmit
channel. Receive suppression attenuates by 24 dB.
4.1.4.1
When TSMde = ‘1’ (Noise Guard ‘off’), the trans-
mit suppressor attenuates the transmit path when
only far-end speech is present. When TSMde = ‘0’
(Noise Guard ‘on’), the suppressor attenuates when
the transmit channel is idle, that is, when no near-
end speech is present.
The purpose of Transmit Suppression is to mask re-
sidual echo by inserting additional loss/attenuation
in the transmit path in the scenario when far-end
speech is present; the residual echo, if any, in dou-
ble-talk is masked by near-end speech, assuming
reasonable levels of ERLE.
There are four controls that govern the behavior of
Transmit Suppression. These are TSThd (Register
3, bits 7 and 6), TSAtt (Register 3, bits 15 and 14),
TSBias (Register 3, bits 5 and 4), and TSMde (Reg-
ister 0, bit 4). TSThd is the primary control and
should be adjusted before changing the value of
TSBias from its default setting. TSThd sets the
ERLE expectation to be used in discriminating be-
tween near-end speech and far-end echo. This con-
trol setting will by far predominate in affecting the
manner in which Transmit Suppression behaves.
TSAtt controls the amount of attenuation added to
the transmit path when the transmit suppressor en-
gages.
TSBias is a secondary control. This is to be adjust-
ed after the system designer is more or less satisfied
with the behavior of Transmit Suppression with the
TSThd set. It affects the ease with which a near-end
talker may disengage Transmit Suppression and
DS295F1
Transmit Suppression
keep it disengaged. We recommend using larger
values of TSBias relative to TSThd settings in or-
der to facilitate ease of near-end speech transmis-
sion. For example, the default setting for TSThd is
15 dB and 18 dB for TSBias.
In some scenarios, especially when the dynamic
range of volume control is significantly large, we
also recommend the use of different combinations
of TSThd and TSBias setting relative to output vol-
ume of the acoustic interface. Specifically, higher
volume levels may call for larger values of TSThd.
TSMde controls the Noise Guard feature. When
TSMde = ‘0’ (Noise Guard enabled), the transmit
suppressor is engaged when no near-end speech is
present. When TSMde = ‘1’ (Noise Guard dis-
abled), the transmit suppressor is engaged only
when far-end speech is present in the absence of
near-end speech.
4.1.4.2
The receive suppressor is nominally attenuating
unless far-end speech is present. This behavior is
more consistent with behavior observed in modern
speakerphones, and helps keep noise levels low.
One side effect of this scheme is that a constant
power signal, such as noise from a noise generator
or a tone, will eventually be attenuated when the
background noise level estimate turns off the re-
ceive suppression speech detector. See Section
4.1.1.4, “Speech Detection” from more details.
RSThd (Register 2, bits 13 and 12) sets the speech
detection threshold of the suppressor’s speech de-
tector. This control is normally set to the same val-
ue as RHDet. See Section 4.1.1.4, “Speech
Detection” for more details.
4.1.4.3
In full-duplex hands-free to full-duplex hands-free
scenarios (where a call exists between two full-du-
plex speakerphones), stability problems can arise at
higher volume levels due to the acoustic coupling
Receive Suppression
Double-talk Attenuation
CS6422
CS6422
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