WM8608 datasheet(37/54 Pages) WOLFSON

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WM8608

PP Rev 1.5 March 2004

An auto-mute function is provided that automatically mutes the output stage when a digital silence

period is detected. Digital silence is defined as a consecutive period of 1024 zero input samples at

the output of the volume control. Auto-mute will be removed as soon as the volume control output

becomes non-zero. (Please note that on the sub channel the noise level is greatly reduced, rather

than complete digital silence.)

To achieve digital silence, you can do one of the following:

•

Turn on auto-mute and set the volume control to zero.

•

Turn on auto-mute and input zero data on the serial data input pins with the bass

management filters disabled. (Page 29)

•

Turn on auto-mute and soft mute.

The auto-mute operates independently across all channel pairs, and can be enabled or disabled on

individual channel pairs.

The mute features maximize the SNR of the PWM amplifier system. Soft-mute will only maximize the

SNR of channel pairs that have auto-mute enabled.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

SMUTE

Digital Soft Mute

0 = disable (signal active)

1= enable

AMUTEF

Front Auto-mute

0 = disable

1 = enable

AMUTES

Surround Auto-mute

0 = disable

1 = enable

AMUTEC

Front Centre and Rear Centre Auto-

mute

0 = disable

1 = enable

R12 (0Ch)

Mute

AMUTESB

Subwoofer Auto-mute

0 = disable

1 = enable

Table 35 Mute

DYNAMIC PEAK COMPRESSOR

The WM8608 includes a Dynamic Peak Compressor for each channel, which prevents the

occurrence of digital clipping when gains in excess of 0dB are applied. The compressor automatically

adjusts the signal amplitude to allow headroom for the LFE boost, sub-woofer mixing, tone controls,

loudspeaker equalisation and digital volume control. The compressor has a programmable limit

threshold, programmable attack and decay time-constants, a frequency-dependent decay mode, and

built-in zero-cross detect. The compressor can be configured either to operate independently on all

channels (DUAL MONO), or on linked channel-pairs (STEREO), e.g. Table 36. The following

channels are paired together: Front-Left and Front-Right, Surround-Left and Surround-Right, Front-

Centre and Rear-Centre.

COMPRESSOR THRESHOLD

The compressor has a digital peak detector which tracks the maximum input signal level at the

output of the volume control. With reference to Figure 22, if this signal is below the threshold set by

control bit THRESH, the compressor operates transparently with no change to the signal level.

However, if peak signal rises above the threshold, the gain through the compressor is modified so

that the upper part of the curve is followed. This ensures that the output signal does not exceed 0dB.

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