Cirrus Logic CS4234 - Manual (Page 45)

DS899F1 45
CS4234
Two control parameters allow the user to limit the ramp-rate range to achieve optimum effect. The MIN
DELAY[2:0] setting limits the maximum ramp rate; higher values will introduce more lag in the envelope
tracking while providing a smoother ramp. The MAX DELAY[2:0] setting limits the minimum ramp rate;
lower values will permit closer tracking of the envelope but may reintroduce zipper noise. The default val-
ues of these registers are recommended as a starting point. It is possible to disable the volume envelope
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 8 .
USER: Change
Volume or Mute
Register
Wait State
Envelope Counter
Running
Envelope
Counter
Timed Out?
Yes
No
Reset Envelope
Counter
Limit Ramp Rate
Reset Envelope
Counter
Ramp Rate =
MUTE_DELAY
Changes Volume Between Time
Setting Volume Current - Setting Volume New
Rate Ramp 
MIN_DELAY
MAX_DELAY
Figure 30. Soft Ramp Behavior