Cirrus Logic CS4271 - Manual (Page 31)

CS4271
DS592F1 31
A system calibration performed in this way will eliminate offsets anywhere in the signal path between the calibration
point and the CS4271.
5.2.8 Interpolation Filter
To accommodate the increasingly complex requirements of digital audio systems, the CS4271 incorporates select-
able interpolation filters for each mode of operation. Fast and slow roll-off filters are available in each of Single, Dou-
ble, and Quad Speed modes. These filters have been designed to accommodate a variety of musical tastes and
styles. The FILT_SEL bit in the DAC Control register (02h) is used to select which filter is used. By default, the fast
roll-off filter is selected.
Filter specifications can be found in Section 3. Plots of the data are contained in the “Appendix” on page 47.
5.2.9 De-Emphasis
Three de-emphasis modes are available via the Control Port. The available filters are optimized for 32 kHz,
44.1 kHz, and 48 kHz sampling rates. See Table 13 for de-emphasis selection in Control Port Mode.
5.2.10 Oversampling Modes
The CS4271 operates in one of three oversampling modes based on the input sample rate. Mode selection is de-
termined by the M1 and M0 bits in the Mode Control 1 register. Single-Speed mode supports input sample rates up
to 50 kHz and uses a 128x oversampling ratio. Double-Speed mode supports input sample rates up to 100 kHz and
uses an oversampling ratio of 64x. Quad-Speed mode supports input sample rates up to 200 kHz and uses an over-
sampling ratio of 32x. See Table 11 for Control Port Mode settings.
5.3 De-Emphasis Filter
The CS4271 includes on-chip digital de-emphasis. Figure 11 shows the de-emphasis curve for Fs equal to 44.1 kHz.
The frequency response of the de-emphasis curve will scale proportionally with changes in sample rate, Fs. Please
see section 5.1.8 for the desired de-emphasis control for Stand-Alone mode and section 5.2.9 for control port mode.
The de-emphasis feature is included to accommodate audio recordings that utilize 50/15 µS pre-emphasis equal-
ization as a means of noise reduction.
De-emphasis is only available in Single Speed Mode.
Gain
dB
-10dB
0dB
Frequency
T2 = 15 µs
T1=50 µs
F1 F2
3.183 kHz 10.61 kHz
Figure 11. De-Emphasis Curve