values give stronger echo suppression, but less full duplex. Range: 0~0x20
0x23BC _tdpf_pf_z_factor_exp_extre me
Strength of AEC postfilter when: no DT (td_lf_vad<=0,
aec_wrong_vad_cntr>0) Higher values gives stronger echo
suppression, but less full duplex
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0x23B5 _tdpf_pf_coef_gain Full duplex enhancement factor when DT detected meanwhile echo doesn’t dominate. It's possible to let more echo pass through, too! Range: 0~0x7FFF
0x23B7 _pf_wait Estimated length for
echo tail coverage (frames) ， each frame means 16ms Range: 0~0x32
0x23B8 _tdpf_min_attn_NE pf gain under the case of DT detected meanwhile small echo. PF gain under different cases
0x23B9 _tdpf_min_attn_no_NE pf gain under the case of small echo only(no DT). 0x23BA
_tdpf_max_attn_no_DT pf gain under the case of Big echo only(no DT). PF gives the heaviest echo suppression
0x23A5 _fqpara_pf_start_bin Decide which band will be applied into PF function. At frequency < DM0x23a5 * 31.25Hz,
don't apply PF gain. RANGE: 0x0~0x10
0x23BE _lfvad_noise_thrd A threshold for DT detection noise floor. Bigger value makes detection harder. if td_lf_vad false alarm under Echo + noise case, set the value smaller to make td_lf_vad detection harder.
0x23BF _lfvad_addon_thrd Also threshold for DT detection. Bigger value makes detection harder. This is used together with lfvad_noise_thrd.
Criterion: Pure echo cancellation should be clean, allow more NE voice pass during DT. When stationary noise exists, need to control the noise up and down to a reasonable level.
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Please note the following
To investigate actual target device (e.g. PDA) mockup’s spectrum character ?NE and FE spectrum difference, follow this procedure below:
1） Play NE and FE voice with Para[0x2310, _linein_HPF_sel]=0x80, then record from
mic0 (0x23f1,signal_pass[0]), find their cross point on the whole.
2） Select right Line-in HPF by setting Para[0x2310, _linein_HPF_sel] by NE/FE spectrum cross point. As an example, if the desired crossing point is 360Hz, then the Bit Bit[0] and Bit[2] of Para[0x2310, _linein_HPF_sel] are set to select 360Hz line-in path HPF and 270Hz LPF for td_lf_vad detection. 3） Fine tune modules before FD.
4）Play NE and FE voice, fine tune Para[0x23BE, _lfvad_noise_thrd] and Para[0x23BF _lfvad_addon_thrd] then check td_lf_vad. It should be on when there is DT or NE, and should keep off when there is only echo.
5）Play NE and FE voice under ambient noise environment, then fine tune Para[0x23BE, _lf_noise_vad_thrd] . Td_lf_vad should not flash for only noise or noise+echo case.
6） TDPF tuning: Check to make sure that vad3 is fine tuned, then tune Para[0x23B3~0x23B5], Para[0x23b3].
? _tdpf_pf_z_factor_exp_high] is used for only FE exists.
? Para[0x23b4, _tdpf_pf_z_factor_exp_low] and the following 3 parameters Para[0x23b5, _tdpf_pf_coef_gain], Para[0x23b8, and _tdpf_min_attn_NE] are all used for DT.
? Normally Para[0x23b4, _tdpf_pf_z_factor_exp_low] < Para [0x23b3, _tdpf_pf_z_factor_exp_high]
7） PF gain applying in FD Para[0x23A5, _fqpara_pf_start_bin] decide that PF gain won’t be applied at frequency < Para[0x23A5, _fqpara_pf_start_bin] * 31.25.Hz .
Normally, it is decided by the cross point of NE/FE. Bigger value means less echo cancellation and more DT.
8） Echo tail - If echo still exists with corresponding fe_vad not flash, the echo is called echo tail. For some application cases, such as small vehicle chassis, the echo tail is easily captured. Para[0x23B7, _pf_wait] estimates the length for echo tail coverage (frames) ，each frame means 16ms. Such as the echo tail lasts for 120ms ? 48/16=3. If the Para[0x23B7, _pf_wait] is set as 3, extra echo cancellation will continue even when no fe_vad inside 48ms, so it also will affect DT and NE.
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7.5 Lineout Equalizer
Lineout equalizer will apply 23-band equalization in the sending direction. It is commonly used to compensate for the frequency response on the microphone to line-out data path. The control parameters of lineout equalizer are described in the following table, and the SAMTuner supplies easier tuning for this module with a graphical user interface (GUI). Table 10: Line-out Equalizer parameters Address
Parameter name Description 0x2390~0x2395
_fqpara_equal[0~5] 23-band Line-out EQ. 0x4444 means 0dB gain on all bands. _fqpara_equal [0] defines the gain on band1~band4:
Bit[15~12] (109.375Hz ~ 171.875Hz),