5 interpolation filter, 6 de-emphasis, Figure 16. de-emphasis curve – Cirrus Logic CS4364 User Manual
Page 24: 5 interpolation filter 4.6 de-emphasis, Figure 16, Cs4364
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DS619F1
CS4364
4.5
Interpolation Filter
To accommodate the increasingly complex requirements of digital audio systems, the CS4364 incorporates
selectable interpolation filters for each mode of operation. A “fast” and a “slow” roll-off filter is available in
each of Single-, Double-, or 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
for more details).
When in Hardware Mode, only the “fast” roll-off filter is available.
Filter specifications can be found in
, and filter response plots can be found in
to
.
4.6
De-Emphasis
The CS4364 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.
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