Production Data
WM8945
DF1 FILTER
The DF1 filter is part of the SE1 block. This provides a direct-form 1 standard filter, as illustrated in
Figure 16. The default coefficients give a transparent filter response.
Figure 16 Direct-Form 1 Standard Filter Structure
The DF1 response is defined by the following equations:
y[n] c1x[n] c2 x[n 1] c3 y[n 1]
y
x
c1 c2 z1
H
1 c3z1
The DF1 filter is enabled using the SE1_DF1_L_ENA register bit defined in Table 13. For the
derivation of the other associated registers, refer to the configuration tools supplied with the WM8945
Evaluation Kit.
The DF1 filter can be used to implement very complex response patterns, with specific phase and
gain responses at different frequencies. Typical applications of this type of filter include the
application of refinements or other user-selected filters.
RETUNETM FILTER
The ReTune™ filter is part of the SE2 block. This is a very advanced feature that is intended to
perform frequency linearization according to the particular needs of the application microphone,
loudspeaker or housing. The ReTune™ algorithms can provide acoustic equalisation and selective
phase (delay) control of specific frequency bands. The ReTune™ filters are enabled using the
SE2_RETUNE_L_ENA register bit defined in Table 14.
For the derivation of the other ReTune™ configuration parameters, the Wolfson WISCE™ software
must be used to analyse the requirements of the application. (Refer to WISCE for further information.)
If desired, one or more sets of register coefficients might be derived for different operating scenarios,
and these may be recalled and written to the CODEC registers as required in the target application.
The ReTune™ configuration procedure involves the generation and analysis of test signals as
outlined below.
To determine the characteristics of the microphone in an application, a test signal is applied to a
loudspeaker that is in the acoustic path to the microphone. The received signal through the
application microphone is analysed and compared with the received signal from a reference
microphone in order to determine the characteristics of the application microphone.
PD, May 2011, Rev 4.1
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