WM8944BECSSLASHR datasheet(34/165 Pages) CIRRUS

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WM8944B

Rev 4.3

5-NOTCH FILTER

3D surround

5-notch filter

DF1 filter

L/HPF

Signal Enhancement Block 1 (SE1)

The 5-notch filter is part of the SE1 block. This function allows up to 5 programmable frequency bands

to be attenuated. The frequency and width of each notch is configurable; the depth of the attenuation

may also be adjusted. The default setting is bypass (OFF).

The notch filters are enabled on the left and right channels using the SE1_NOTCH_L_ENA and

SE1_NOTCH_R_ENA register bits defined in Table 13. Note that, although the 5-notch filter can be

enabled on the left/right channels independently, the parameters that define the notch filters apply

equally to the left and right channels, when enabled.

The notch filter coefficients are programmed in registers R72 to R91. For the derivation of these

registers, refer to the configuration tools supplied with the WM8944B Evaluation Kit.

Note that the notch filters should not be configured for centre-frequencies below 120Hz. To apply

filtering at low frequencies, the SE1 High Pass Filter should be used.

Typical applications for the notch filters are filtering of fixed-frequency noise or resonances; these

might arise from a motor (eg. DSC zoom lens motor) or from characteristics of the application

housing. Example plots of the Notch filter response are shown in Figure 14.

Notch Response - Slave Mode - fc=1kHz, fb=1kHz Depth 0 to 100%

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

520

1.5k

550

600 650 700 750 800 850 900

1.2k

Notch Response - Slave Mode - fc=1kHz, fb=100, 500, 1k, 5k, 10kHz -

Depth=100%

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

20k

100

200

500

10k

1kHz notch, bandwidth 1kHz, depth 0% to 100% in 20% steps

1kHz notch, 100% depth, bandwidth 100Hz, 500Hz, 1kHz, 5kHz, 10kHz

Notch Response - Slave Mode - fc=200, 500, 1k, 2k, 5k, 10kHz, fb=fc/2,

Depth 100%

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

100

20k

200

500

10k

6 notches, bandwidth Fcentre/2, depth 100%

Figure 14 Notch Filter Responses

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