Cirrus Logic CS4385 - Manual (Page 27)

DS671F2 27
CS4385
4.6 De-Emphasis
The CS4385 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 20
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.
4.7 ATAPI Specification
The CS4385 implements the channel-mixing functions of the ATAPI CD-ROM specification. The
ATAPI functions are applied per A-B pair. Refer to
Table 9 on page 45 and Figure 21 for additional informa-
tion.
Gain
dB
-10dB
0dB
Frequency
T2 = 15 µs
T1=50 µs
F1 F2
3.183 kHz 10.61 kHz
Figure 20. De-Emphasis Curve
Σ Σ
A Channel
Volume
Control
Aout Ax
AoutBx
Left Chan nel
Audio D ata
Right Chan nel
Audio D ata
B Channel
Volume
Control
MUTE
MUTE
SDINx
Figure 21. ATAPI Block Diagram (x = channel pair 1, 2, 3, or 4)