Cirrus Logic CS4365 - Manual (Page 25)

DS670F2 25
CS4365
4.5 Interpolation Filter
To accommodate the increasingly complex requirements of digital audio systems, the CS4365 incorporates
selectable interpolation filters for each mode of operation. A “fast” and a “slow” roll-off filter is available in
each of Single, Double, and Quad-Speed modes. These filters have been designed to accommodate a va-
riety of musical tastes and styles. The FILT_SEL bit is used to select which filter is used (see the
“Filter
Plots” on page 45 for more details).
When in Hardware Mode, only the “fast” roll-off filter is available.
Filter specifications can be found in Section , and filter response plots can be found in Figures 24 to 47 .
4.6 De-Emphasis
The CS4365 includes on-chip digital de-emphasis filters. The de-emphasis feature is included to accommo-
date older audio recordings that utilize pre-emphasis equalization as a means of noise reduction.
Figure 16
shows the de-emphasis curve. The frequency response of the de-emphasis curve will scale proportionally
with changes in sample rate, Fs if the input sample rate does not match the coefficient which has been se-
lected.
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 then the corner frequencies of the de-emphasis
filter will be 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 16. De-Emphasis Curve