Cirrus Logic AN168 - Manual (Page 21)

AN168
AN168REV2 21
The difference between the two RVol values is the
worst-case ERLE of the echo canceler. Here is the
detailed procedure:
1) Set up the speaker and microphone and mic
preamp gain for -9 dB of acoustic coupling.
2) Configure the CS6422 from reset with the ex-
ception of the following:
a) Mic set to '1' or '0', depending on whether
the internal mic preamp is used or not
b) HDD = ‘1’
c) GB = 0.75 dB/ms
d) TSD = ‘1’
e) ACC = ‘Cleared’
f) Taps = 55.5 ms
g) RSD = ‘1’
h) NseRmp = 12 dB/s
i) PCSen = ‘low’
j) AErle = 18 dB
k) AFNse = -42 dB
l) NECD = ‘1’
m) ASdt = -18 dB
The register configuration which implements the
above is:
reg 0: 5480 (d480 if internal mic preamp is
used)
reg 1: 0a82
reg 2: 0804
reg 3: 2006
reg 4: 5008
reg 5: 018a
3) Set ACC to ‘Normal’.
4) Inject speech or 2.8 Vpp white noise into NI for
5 to 10 seconds. This trains the AEC to the
acoustic path. See Figure 15.
5) Set ACC to ‘Freeze’. Try to minimize the
movement in the acoustic path from here on, as
path changes will adversely affect the ERLE re-
Speaker
Driver
Mic
Preamp
AO
CS6422
APO
TVol - Transmit
Volume
Air Coupling
Mute TVol and train the AEC using speech...
0dB
-?dB
Mute
RVol - Receive
Volume
+0dB
AEC
‘normal’
30dB
+
-
NI
Figure 15. Acoustic ERLE Measurement -- Train the AEC