Cirrus Logic CS4244 - Manual (Page 41)

DS900F1 41
CS4244
tracking and always produce a constant ramp rate. To accomplish this, set the MIN DELAY[2:0] and MAX
DELAY[2:0] values to match the MUTE DELAY[1:0] setting.
The envelope counter time out period which defines the boundary between the two soft-ramping behav-
iors depends on the base rate. It is equal to approximately 100,000/Fs.
The MUTE DELAY[1:0] , MIN DELAY[2:0] , and MAX DELAY[2:0] bits specify a delay equal to a multiple
of the base period between volume steps of 6.02 /
64
dB, which is approximately 0.1 dB. This is the internal
resolution of the volume control engine. Consequently the soft-ramp rate can be expressed in ms/dB as
shown in
Table 6 .
Table 6. Soft Ramp Rates
Full-scale ramp is 96 dB (-90 dB to +6 dB)
4.6.5.3 Noise Gate
The CS4244 is equipped with a Noise Gate feature that mutes the output if the signal drops below a given
bit depth for 8192 samples. While the enabling or disabling of the Noise Gate feature is done for the entire
DAC1-4 output path, each of the channels within the path have separate monitoring circuitry that will trig-
ger the Noise Gate function independently of the other channels. For instance, if the Noise Gate were en-
abled for and one of the channels were to exhibit a pattern of more than 8192 samples of either all “1’s”
or all “0’s”, the output for that particular channel would be muted (and subsequently unmuted), indepen-
dently of the other channels. To enable the Noise Gate feature, set the DAC1-4 NG[2:0] bits to the desired
bit depth. The available bit depth settings are shown in
Table 7 .
Fs = 48 kHz or 96 kHz (Base = 48 kHz) Fs = 32 kHz or 64 kHz (Base = 32 kHz)
Ramp Rate
Time to Ramp
to Full Scale
(ms)
Time to Ramp
6 dB (ms)
ms/dB
Time to Ramp
to Full Scale
(ms)
Time to Ramp
6 dB (ms)
ms/dB
1 x Base 21.33 1.33 0.22 32 2 0.33
2 x Base 42.67 2.67 0.44 64 4 0.66
4 x Base 85.33 5.33 0.89 128 8 1.33
8 x Base 170.67 10.67 1.77 256 16 2.66
16 x Base 341.33 21.33 3.54 512 32 5.32
32 x Base 682.67 42.67 7.09 1024 64 10.63
64 x Base 1365.33 85.33 14.17 2048 128 21.26
128 x Base 2730.67 170.67 28.35 4096 256 42.52
DAC1-4 NG[2:0] Setting Channel is muted after “x” bits
000 Upper 13 Bits (-72 dB)
001 Upper 14 Bits (-78 dB)
010 Upper 15 Bits (-82 dB)
011 Upper 16 Bits (-90 dB)
100 Upper 17 Bits (-94 dB)
101 Upper 18 Bits (-102 dB)
110 Upper 24 Bits (-138 dB)
111 Noise Gate Disabled
Table 7. Noise Gate Bit Depth Settings