Cirrus-logic CS4385 Manuel d'utilisateur télécharger pdf (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

-10dB

0dB

Frequency

T2 = 15 µs

T1=50 µs

F1 F2

3.183 kHz 10.61 kHz

Figure 20. De-Emphasis Curve

ΣΣ

A Channel

Volume

Control

Aout Ax

AoutBx

Left Chan

nel

Audio Data

Right Channel

Audio Data

BChannel

Volume

Control

MUTE

SDINx

Figure 21. ATAPI Block Diagram (x = channel pair 1, 2, 3, or 4)

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 ... 54 55

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Cirrus-logic CS4385 Manuel d'utilisateur Page 27

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