WM8955L
Product Preview
DIGITAL TO ANALOGUE CONVERTER (DAC)
Treble and linear bass enhancement mayproduce signals that exceed full-scale. In order to avoid
limiting under these conditions, it is recommended to set the DAT bit to attenuate the digital input
signal by6dB. The gain at the outputs should be increased by6dB to compensate for the
attenuation. Cut-onlytone adjustment and adaptive bass boost cannot produce signals above full-
scale and therefore do not require the DAT bit to be set.
After passing through the tone control filters, digital ‘de-emphasis’ can be applied to the audio data if
necessary(e.g. when the data comes from a CD with pre-emphasis used in the recording). De-
emphasis filtering is available for sample rates of 48kHz, 44.1kHz and 32kHz.
The WM8955L also has a Soft Mute function, which graduallyattenuates the volume of the digital
signal to zero. This function is enabled bydefault. To playback an audio signal, the WM8955L must
first be unmuted bysetting the DACMU bit to zero.
REGISTER
ADDRESS
BIT
LABEL
DAT
DEFAULT
DESCRIPTION
R5 (05h)
DAC Control
7
0
DAC 6dB attenuate enable
0 = disabled (0dB)
1 = -6dB enabled
3
DACMU
1
Digital Soft Mute
1 = mute
0 = no mute (signal active)
De-emphasis Control
11 = 48kHz sample rate
10 = 44.1kHz sample rate
01 = 32kHz sample rate
00 = No De-emphasis
2:1
DEEMPH
00
Table 4 DAC Control
The digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital
interpolation filters. The bitstream data enters two multi-bit, sigma-delta DACs, which convert them to
high qualityanalogue audio signals. The multi-bit DAC architecture reduces high frequencynoise and
sensitivityto clock jitter. It also uses a Dynamic Element Matching technique for high linearityand
low distortion.
In normal operation, the left and right channel digital audio data are converted to analogue in two
separate DACs. However, it is also possible to disable one channel, so that the same signal (left or
right) appears on both analogue output channels. Additionally, there is a mono-mix mode where the
two audio channels are mixed together digitallyand then converted to analogue using onlyone DAC,
while the other DAC is switched off. The mono-mix signal can be selected to appear on both
analogue output channels (see Analogue Outputs).
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R23 (17h)
5:4
DMONOMIX[1:0]
00
DAC mono mix
Additional (1)
00: stereo
01: mono ((L+R)/2) into DACL, ‘0’ into
DACR
10: mono ((L+R)/2) into DACR, ‘0’ into
DACL
11: mono ((L+R)/2) into DACL & DACR
Table 5 DAC Mono Mix Select
Product Preview Rev 0.4 May2003
18
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
