CS4244 datasheet(39/63 Pages) CIRRUS

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DS900F2

CS4244

4.6.5

Volume Control

The CS4244 includes a volume control for the DAC1-4 signal path. The implementation details for the vol-

ume control and other associated peripheries for DAC1-4 is shown in Figure 29 below. Digital volume

steps, adjustable noise gating, muting, and soft ramping are provided on each DAC channel.

4.6.5.1

Mute Behavior

Each DAC channel volume is controlled by the sum (in dB) of the individual channel volume and the mas-

ter volume registers. The channel and master volume control registers have a range of +6 dB to -90 dB

with a nominal resolution of 6.02/16 dB per each bit, which is approximately 0.4 dB. The sum of the two

volume settings is limited to a range of +6 dB to -90 dB. Any volume setting below this range will result in

infinite attenuation thus muting the channel.

A DAC channel may alternatively be muted by using the mute register bits, the power down bits, or the

Noise Gate feature. For any case when the mute engages (volume is less than -90 dB, power down bit is

set, mute bit is set, or Noise Gate is engaged), the CS4244 will mute the channel immediately or soft-ramp

the volume down at a rate specified by the MUTE DELAY[1:0] bits depending on the settings of the DAC1-

4 ATT. bit in the "DAC Control 3" register. This behavior also applies when unmuting a channel.

4.6.5.2

Soft Ramp

The CS4244 soft ramp feature (enabled using the DAC1-4 ATT. bit) is activated on mute and unmute tran-

sitions as well as any normal volume register changes. To avoid any potential audible artifacts due to the

soft ramping, the volume control algorithm implements the ramping function differently based upon how

the user attempts to control the volume.

If the user changes the volume in distant discrete steps such as what would happen if a button were

pressed on a user interface to temporarily add attenuation to or mute a channel, then the volume is

ramped from the current setting to the new setting at a constant rate set by the MUTE DELAY[1:0] bits.

Alternatively, if the user controls the volume through a knob or slider interface, a volume envelope is sam-

pled at a slow, not-necessarily uniform rate (typically 1-20 Hz) and sent to the CS4244. In this case the

ramping algorithm detects a short succession of volume changes attempting to track the volume envelope

and dynamically adjusts the soft-ramp rate.

If the CS4244 were to use a constant ramp rate between the volume changes it receives, its output volume

envelope may either lag behind the user-generated envelope if the ramp rate is set too low (possibly not

reaching the peaks and dulling the envelope) or the output volume envelope may cause a stair-case effect

resulting in audible zipper noise if the ramp rate is set too high. By instead adapting the soft-ramp rate to

fit the envelope given by the incoming volume samples, the envelope lag time is limited and the zipper

Noise Gate

Soft Ramp

DACx Data

DACx Volume

Master Volume

Interpolation

Filter

Modulator

DAC

Limiter

(+6 to -90 dB)

INV DACx

DAC1-4 Noise

Gate Threshold

MUTE DACx

DAC1-4 ATT

AOUTx

Figure 29. Volume Implementation for the DAC1-4 Path

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