Cirrus Logic CS4244 - Manual (Page 40)

DS900F1 40
CS4244
noise is avoided. In this mode the soft ramp algorithm linearly interpolates the volume between the volume
changes. There is a lag of one volume change sample since two samples are required to calculate the
first ramp rate.
See Figure 30 for the soft ramp diagram. On the first volume sample received, the CS4244 only detects
the possible beginning of a volume envelope sequence and resets an envelope counter. The volume
starts ramping to the new volume setting at a constant rate controlled by the
MUTE DELAY[1:0] setting.
If the envelope counter times out before a new volume sample is received, the next received sample is
treated in the same way as the previous sample and the ramp rate is kept constant. In this way, as long
as the volume samples are distant from each other by more than the envelope counter time out, the rate
is kept constant resulting in the soft-ramp behavior described in the button-press example.
However if the next volume sample is received before the envelope counter times out, then it is assumed
to be part of a volume envelope sequence. The envelope counter is reset and as long as new samples
are received in succession before a time out occurs, the sequence is continued. Starting at the second
volume sample of an envelope sequence, the ramp rate is adjusted using the equation shown in
Figure 30 .
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 re-introduce zipper noise. The default val-
ues of these registers are recommended as a starting point. It is possible to disable the volume envelope
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