Gain factor initialization
0x2370 _ss_bounds_high[2] extra gain factor for noise suppression when no big echo, will be applied if voice probability very low, bigger value can reduce watering sound. Range: 0~0x7FFF
0x2373 _fqpara_gndL_div Noise tracking factor to adapt to not so stable stationary noise. Larger value when outside noise goes up and down frequently. (180~440Hz). Range: 0~0x7FFF Noise ground
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0x2374 _fqpara_gndM_div Noise tracking factor for 440~2300Hz. Range: 0~0x7FFF
0x2375 _fqpara_gndH_div Noise tracking factor for 2300~7500Hz. Range: 0~0x7FFF
0x2384 _fqpara_snr_order Threshold for speech SNR, higher value will suppress more noise and keep less voice. Range: 0~0x9
SNR_ADJUST, which is controlled by bit 7 of
Para[0x2303, _kl_config]
0x239C _fqpara_inbeam_dec Weakens NS when SNR is very high. Higher value improves voice quality in quiet environment, but also raises noise floor. Therefore, it needs to be tuned together with idle noise suppression. Range: 0~0x7FFF 0x23E D
_idle_noise_thrd idle noise suppression will be applied if noise level lower than this threshold. Bigger value will make idle noise cut more active. Range: 0~0x7FFF IDLE noise , which is
controlled by bit 8 of
Para[0x2303,
0x23EE _idle_ins_attn The suppressing level for idle _kl_config] noise, 0x7fff is unit gain. Range: 0~0x7FFF
Criterion: Pure NS should be stable without obvious watering sound; NS for NE with noise should have no obvious noise up when NE and noise down between NE interval as well as keeping more small NE voice. Please note the following:
FDNS parameters are user preference settings. If the default can’t be accepted, the following steps are recommended:
1） Step 1: FDNS level has direct relationship with Para[0x236E~0x2370], normally when adjust NS level to smaller (Para[0x236E, _ss_bounds_high[0]) with heavier suppression, need to adjust gain factor to bigger (Para[0x236f~0x2370]) to avoid noise up and down at the same time;
2） Step 2: Para[0x2384, _fqpara_snr_order] is a fine-adjustment compensation parameter, generally used for different chassis related to the talker mouth to phone microphone distance, depending on the phone type. The default is using bartype phone.
3） Step 3:Only when the suppressed stationary or non-stationary noise has special high residue for some frequency range, Para[0x2373~0x2375] can be considered to raise
for related frequency range to get more stable noise suppression;
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4） Step 4: Para[0x239c~0x239e] allow the user to exercise fine control over nonstationary noise reduction based on observed signal-to-noise ratio(SNR). Para[0x239c] is for SNR observed in beam.
5） Step 5: Idle noise sub module will generate a suppressed gain which will be applied at the point of mic_volume in the gain flow. So if you use modules turn on/off to see the modules before mic_volume apply, remember to turn off idle noise. It is used to make high SNR cases with more clean noise floor, and can be tuned together with Para[0x239C, _fqpara_inbeam_dec] for more favorable voice quality and reasonable noise floor.
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7.4 Frequency Domain Echo Cancellation
Frequency domain includes NS and echo cancellation functions. It can be turned on or off by setting or clearing bit0 of Para[0x2303, _kl_config]. Frequency domain echo cancellation can be considered as a kind of non-stationary NS together with PF gain apply in frequency domain. There are some key parameters affecting its performance as listed in the table below:
Table 9: Frequency Domain Echo Control parameters Address Parameter name Description Sub Module 0x2380 _fqpara_beta_uv_fe Beta2 weight for FE only Range: 0~0x7FFF UND
0x2381 _fqpara_beta_mixed_fe Beta2 weight for Double- Talk
Range: 0~0x7FFF
0x23EE _idle_ins_attn The suppressing level for idle noise, 0x7fff is unit gain
Range: 0~0x7FFF
0x23B3 _tdpf_pf_z_factor_exp_high Strength of AEC postfilter at no double talk. A larger value results in stronger echo
suppression, but less full duplex. Range: 0~0x20 TDPF , which is controlled by bit 9 of Para[0x2304, _sp_flag]
0x23B4 _tdpf_pf_z_factor_exp_low Strength of AEC at double talk. Higher