13 0x000e Vad04 subband vad0 for 2328Hz ~4000Hz 14 0x000f Vad05 subband vad0 for 4000Hz ~6800Hz
15 0x0010 Td_lf_vad The VAD to indicate the low frequency double talk
16 0x0011 Aec_wrong_vad_cntr Cntr to show aec wrong or not 17 0x0012 DR_bin_cnt The VAD to indicate the far end signals,looser than Fe_vad_li.
18 0x0013 Fe_vad_li_fq The VAD to indicate the far end signals 19 0x0018 Vad0_pop The molulated near end voice vad
The indices 8~19 in the above are frequently used VADs that users often need to examine during perform module performance tuning. The following are some detailed description of the VADs.
1） FE_VAD: It is judged in linear AEC module and controls the latter echo cancellation related modules. When there is FE voice, FE_VAD should be on; must turn on bit8 of Para[0x2304,_sp_flag] to observe FE_VAD.
2） FE_VAD_BIG: It is judged in linear AEC module and controls the latter echo cancellation related modules. When FE voice is big, FE_VAD_BIG should be on; must turn on bit8 of Para[0x2304,_sp_flag] to observe FE_VAD_BIG.
3） FE_VAD_LI: It is judged in FENS module and controls AEC and the latter echo cancellation related modules. When FE voice exists, FE_VAD_LI should be on; must turn on bit14 of Para[0x2303,_kl_config] to observe FE_VAD_LI.
4） Td_lf_vad : It’s used to indicate Double Talk and associated with post filter, speaker
attenuation, Fq_NS process. Td_lf_vad is judged in time domain. Under no ambient noise case, if there is NE or double talk, td_lf_vad should be on.
5） VAD01~VAD05：They are subband vad0 which are judged in frequency domain when FE doesn’t exist. When there is only NE (no double talk) under high SNR condition, vad01~vad05 should be on.
6） Vad0_pop: the mixture of vad0 and vad01 ~ vad05.
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7.0 Performance Tuning Procedure Details 7.1 Linear AEC
Linear AEC is the first echo cancellation module to cancel linear echo. It can be turned on or off by setting or clearing bit 8 of Para[0x2304, _sp_flag]. Table 6: Linear AEC parameters Index Address
Parameter name Description
1 0x2339 tdaec_delay_length Additional buffer to account for the Codec delay of the AEC path. Maximum: 0x68, Minimum:0
2 0x232f aec_ref_gain Gain for AEC ref channel. Unit gain: 0x100 3 0x2337 tdaec_nw_shift Control convergent speed and convergent stability. Bigger value will make convergence faster and more unstable. Range:0xFFF0~0
4 0x2333 tdaec_fe_vad_th Threshold for fe_vad decision. Lower values
can cause more active echo cancellation. Range: 0~0x7FFF
5 0x2332 tdaec_fe_vad_th_high Threshold for fe_vad_big decision. Higher values can increase vad0 decision and decrease frequency domain echo suppression, the effect is less echo suppression and more full duplex maintained. Range: 0~0x7FFF
Criterion: For NE signals, the processed signal should be nearly same as the input of linear AEC; For FE signals, the processed signal should have above 15dB attenuation. Normally good AEC performance can achieve above 18dB echo cancellation. Please note the following:
1） Para[0x2339, aec_delay_length] - it can be used to compensate for long delay between echo (0x23f1, signal_Pass[0]) and AEC reference input (0x23ff,
signal_pass[14]) signals. By recording the two signals, tone signal is suggested to be played as the linein, the actual delay D1 can be measured. Make sure that
Para[0x2339, aec_delay_length] is smaller than D1, otherwise linear AEC can’t work. 2） Para[0x232f, aec_ref_gain] - it is used to balance the power difference between echo and AEC reference input signals. Check AEC reference input (0x23ff, signal_pass[13]) signals to make sure it is not saturated.
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7.2 Frequency Domain Activity Detectors
These are the key parameters for VAD01, VAD02, VAD03, VAD04, and VAD05 Table 7: Voice Activity Detectors - VAD01, VAD02, VAD03, VAD04, VAD05
Index Address Parameter name Description
1 0x2382 _fqpara_vad_thrd_low SNR threshold for vad01. if sub-band SNR smaller than this threshold. Range: 0~0x7FFF
2 0x2383 _fqpara_vad_thrd_high SNR threshold for vad02~vad05. if sub-band SNR smaller than this threshold. Range: 0~0x7FFF Criterion：
VAD01, VAD02, VAD03, VAD04, and VAD05 are similar to subband vad0 under high SNR, which won’t flash when FE exists and should flash when in-beam NE voice exists for corresponding subband.
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7.3 Frequency Domain Noise Suppression
Frequency domain includes NS and nonlinear echo cancellation functions. It can be turned on or off by setting or clearing bit0 of Para[0x2303, _kl_config].
Frequency domain NS supply non-stationary NS and stationary NS for HS mode and only supply stationary NS for 2mic HF and 1mic HF mode. There are some key parameters affecting its performance as listed in the table below:
Table 8: Frequency Domain Noise Suppression (FDNS) parameters
Address
Parameter name Description Sub Module
0x236E _ss_bounds_high[0] Noise suppression level, 0x7fff is
unit gain, means 0db noise suppression, smaller value makes heavier noise suppression and less voice pass. Range: 0~0x7FFF
0x236F _ss_bounds_high[1] base gain factor for noise suppression, will be self-doubled if vad01 ≤ 0. A larger value means heavier suppression and less voice passed thru. Range: 0~0x7F7F Bit[15~8]: base gain factor for f < 2350Hz component;
Bit[7~0]: extra gain factor on base gain for f ≥ 2350Hz component after left banked; Default value = 0x0B80 but it is improper, please configure it to 0x0B05. this means 0x0B00 as gain factor for f < 2350Hz, and 0x1000 = (0xB00 + 0x500) as gain factor for f ≥ 2350Hz.