Bit[3~0] (5484.375Hz ~ 5984.375Hz);
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_FENS_equal [5] defines the gain on band21~band23:
Bit[15~12] (5984.375Hz ~ 6484.375Hz), Bit[11~8] (6484.375Hz ~ 6984.375Hz), Bit[7~4] (6984.375Hz ~ 7984.375Hz). The gain on each band represented by a 4-bit Gain index -
0: +6dB, 1: +4dB, 2: +2dB, 3: +1dB, 4: 0dB, 5: -1dB, 6: -2dB, 7: -4dB, 8: -6dB, 9: -8dB, A: -10dB, B: -13dB, C: -16dB, D: -20dB, E: -30dB, F: -50dB.
Criterion: Pure NS should be stable without obvious watering sound; NS for FE with noise should has no obvious noise up when FE and noise down between NE interval as well as keeping more small FE voice.
Please note that if the FENS is turned off, then lineout equalizer won’t work because it is a sub module of FENS.
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7.8 Bright Voice Enhancement (BVE)
BVE module will control the output gain of the receiving direction by the ambient noise collected by mic, high ambient noise will lead to higher gain to bright the spkout voice. It can be turned on/off by setting/clearing bit 4 of Para[0x2305, _ft_flag]. There are some
key parameters affecting its performance as listed in the table below: Table 12: Bright Voice Enhancement (BVE) parameters Address
Parameter name Description 0x22D3
_AVC_SNR_thrd Works when Bit[4] of 0x2305 is ON. This sets the SNR threshold to trigger be action, smaller value means it is harder to trigger be 0x22D4
_AVC_vol_thrd Works when Bit[4] of 0x2305 is ON The threshold to trigger frequency adjustment (decrease low and increase high freqency). When avc_gain_out >threshold, it will trigger the frequency adjustment.
DM address for avc_gain_out: 0x380F
Criterion: Subjective test with noisy environment, turn on BVE can obviously hear the speaker out bigger. Continuous NE voice shouldn’t boost speakout by BVE.
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7.9 Bandwidth Extension (BWE)
Band Width Extension (BWE) is designed to enhance narrow bandwidth voice signal from [200, 3400]Hz to [120, 7400] Hz on downlink path. This feature is supported only when DSP is on Slave mode.
? When CODEC and PCM/I2S are both 16kHz (host already duplicated PCM/I2S input
data of 8kHz sampling voice signal to 16kHz by repeating each sample). BWE is supported in both digital and analog interface. Set Bit[11] of Para[0x2305, _ft_flag] to turn on BWE.
? When CODEC is on 16kHz, while PCM/I2S is on 8kHz, DSP will duplicate PCM/I2S input each sample to form a 16kHz voice data. In this case, BWE is only supported in DAC analog interface. To turn on BWE feature, set Bit[11] of Para[0x2305, _ft_flag] and set Bit[4] of Para[0x2301, _sample_rate].
? The index of EQ gains for BWE 4KHz higher component is designated in parameter DM0x2399 and DM0x239A. Their default values are 0xBBCD and 0xEEFF respectively.
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7.10 Far Field Pickup (FFP)
FFP function is combined by Lout-AGC module and Lout-DRC module, so you can turn on this feature by the following switch: 0x2304 bit [15]=1 and 0x2303 bit [12] =1 at the same time.
Lout-AGC module implement adaptive gain control when talk from different fields, such as for far-field talk, we expect increase lout-gain to get standard output; otherwise, for nearfield talk, decrease lout-gain to get output as the similar standard level.
Lout-DRC module implement dynamic range control, in this FFP function, we expect to get the following effect: when talk switches between near field and far field, output remains a fixed range.
Table 13: Far Field Pickup parameters Index Address Parameter name Description
1 0x2304 bit [15] Lout-AGC feature switch This bit is set to 1, turn on Lout- AGC
2 0x2303 bit [12] Lout-DRC feature switch This bit is set to 1, turn on Lout- DRC
3 0x2360 _fdmicagc_minagc Minimum gain, -10dB (0x800 is unit gain)
Range:0x100~0x800.
4 0x2361 _fdmicagc_maxagc Maximum gain, +10dB (0x800 is unit gain)
Range:0x800~0x2000.
5 0x2362 _fdmicagc_alpha_up Smooth factor of power estimation for AGC control when voice on, the smaller then faster. Range:0x1~0x7E00.
6 0x2363 _fdmicagc_alpha_down Smooth factor of power estimation for AGC control when voice off, the smaller then faster. Range: 0x1~0x7E00.
7 0x2364 _fdmicagc_ref_low Lout-AGC level controller. Big values lift up the adjustable lout power range.
(Observe DM0x2366 for current
Lout-AGC gain, to match your expected output level with unit gain)
Range: 0x1~0x400
8 0x380c _mic_agc_gain Real-time gain applied, 0x800 is unit gain.
NOTE: this is variable for observation, not for tuning.
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10 0x23D3 _lout_drc_level Level for Lout-DRC module Range: 0x1~0x4000
11 0x23D4 _lout_drc_slant The control speed for Lout-DRC module, the bigger then faster. Range: 0x1000~0x7F00
Performance optimization recommendations: For Lout-AGC module,
1. First select your control range by your application; such as talk field from 30cm to 5m, the difference of measured power level between 30cm and 5m is about 18dB, then your control range should bigger 18dB. We suggest select 6dB bigger range (in this case: 24dB)
2. Select minimum and maximum boundary by control range. In this sample, you can
select (-12dB, +12dB), or (-18dB, +6dB), or (-6dB, +18dB), or others, but we suggest the best sequence for your choice is as follows:(-18dB, +6dB): this is down