CS4364 datasheet(24/50 Pages) CIRRUS

24 / 50 page

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 “Parameter

Definitions” on page 47 for more details).

When in Hardware Mode, only the “fast” roll-off filter is available.

Filter specifications can be found in Section 2, and filter response plots can be found in Figures 24 to 47.

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. 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

-10dB

0dB

Frequency

T2 = 15 µs

T1=50 µs

3.183 kHz

10.61 kHz

Figure 16. De-Emphasis Curve

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