Cirrus Logic CS4385A - Manual (Page 26)

26 DS837F2
CS4385A
4.5 Interpolation Filter
To accommodate the increasingly complex requirements of digital audio systems, the CS4385A incorpo-
rates selectable interpolation filters for each mode of operation. A “fast” and a “slow” roll-off filter is available
in each of the three speed modes, Single-, Double-, and Quad-Speed. These filters have been designed to
accommodate a variety of musical tastes and styles. The FILT_SEL bit is used to select which filter is used
(see the
“Filter Plots” on page 48 for more details).
When in Hardware Mode, only the “fast” roll-off filter is available.
Filter specifications can be found in Section 1 , and filter response plots can be found in Figures 27 to 50 .
4.6 De-Emphasis
The CS4385A includes on-chip digital de-emphasis filters. The de-emphasis feature is included to accom-
modate older audio recordings that use pre-emphasis equalization as a means of noise reduction.
Figure 19
shows the de-emphasis curve. The frequency response of the de-emphasis curve scales proportionally with
changes in sample rate, Fs, if the input sample rate does not match the coefficient that has been selected.
In Software Mode, the required de-emphasis filter coefficients for 32 kHz, 44.1 kHz, or 48 kHz are selected
via the de-emphasis control bits.
In Hardware Mode, only the 44.1 kHz coefficient is available (enabled through the M2 pin). If the input sam-
ple rate is not 44.1 kHz and de-emphasis has been selected, the corner frequencies of the de-emphasis
filter is scaled by a factor of the actual Fs over 44,100.
Gain
dB
-10dB
0dB
Frequency
T2 = 15 µs
T1=50 µs
F1 F2
3.183 kHz 10.61 kHz
Figure 19. De-Emphasis Curve