WM8523 datasheet(30/51 Pages) WOLFSON

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WM8523

Production Data

PD, Rev 4.1, August 2011

Ramp Volume Changes

If ramp volume changes are selected, the ramp rate is dependent upon the sampling rate. The ramp

rates for common audio sample rates are shown in Table 15.

SAMPLE RATE FOR DAC (kHz)

GAIN RAMP RATE

(ms/dB)

0.25

44.1

0.18

0.17

88.2

0.1

0.08

176.4

0.05

192

0.04

Table 15 Volume Ramp Rate

For example, when using a sample rate of 48kHz, the time taken for a volume change from an initial

setting of 0dB to -20dB is calculated as follows:

Volume Change (dB) x Volume Ramp Rate (ms/dB) = 20 x 0.17 = 3.4ms

Zero cross is not used when ramping. The volume level in the DAC is set by the user in 0.25dB

increments, but during the volume ramp increments of 0.125dB are actually used. This step size is

inaudible and means there is no requirement to wait until a zero crossing occurs. Another benefit of not

using zero cross when ramping is that predictable ramp times are produced – there is no signal

dependency on the ramp time.

Step Volume Changes and Zero Cross

The step volume control includes optional zero cross functionality. When zero cross is enabled, by

setting DAC_ZCEN=1, volume changes are not applied until the signal crosses zero so no discontinuity

is seen in the output signal. Zero cross helps to prevent pop and click noise when changing volume

settings and is therefore recommended if using step volume changes.

The zero cross function includes a timeout which forces volume changes if a zero cross event does not

occur. The timeout period is 14400 samples, equivalent to 300ms at 48kHz sample rate.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

DAC_CTRL3

05h

DAC_

ZCEN

Zero Cross Enable

0 = Do not use zero cross

1 = Use zero cross

Table 16 Zero Cross Control

Table 17 gives a summary of the volume mode settings and their effect.

DAC_VOL_

UP_RAMP

DAC_VOL_

DOWN_RAMP

DAC_ZCEN

VOLUME CHANGE

DOWN

Step, no zero cross

Ramp

Step, no zero cross

Ramp

Step, use zero cross

Ramp

Step, use zero cross

Ramp

Table 17 Volume Change Summary

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