Texas Instruments TAS3002 manual Audio Control/Enhancement Functions, Soft Volume Update

4 Audio Control/Enhancement Functions

4.1 Soft Volume Update

The TAS3002 device implements a TI proprietary soft volume update. This feature allows a smooth and pleasant-sounding change from one volume level to another over the entire range of volume control (18 dB to mute).

The volume is adjustable by downloading a gain coefficient through the I2C interface in 4.16 format—4 bits for the integer and 16 bits for the fractional part. NO TAG lists the 4.16 coefficients converted into dB for the range of – 70 dB to 18 dB with 0.5-dB step resolution.

Right and left channel volumes can be unganged and set to different values. This feature implements a balance control.

Volume is changed by writing the desired value into the volume control registers. This is done by asserting the volume-up or volume-down GPI terminal (see Section 7.6.1) for a limited range of volume control. Alternatively, volume control settings can be sent to the TAS3002 device over the I2C bus.

4.2 Software Soft Mute

Soft mute is implemented by loading all zeros in the volume control register. This causes the volume to ramp down over a duration of 2048fS samples to a final output of 0 (− infinity dB).

Soft mute can be enabled by either asserting the mute GPI terminal (see Section 7.6.1) or sending a mute command over the I2C bus. Subsequent assertions of the mute GPI terminal toggle soft mute off and on.

4.3 Input Mixer Control

The TAS3002 device is capable of mixing and multiplexing three channels (SDIN1, SDIN2, and the ADC output) of serial audio data. The mixing is controlled through three mixer control registers. This is accomplished by loading values into the corresponding bytes of the mixer left gain (07h) and mixer right gain (08h) control registers. See Figure 4−1 for a functional block diagram of the input mixer.

The values loaded into these registers are in 4.20 format—4 bits for the integer and 20 bits for the fractional part. NO TAG lists the 4.20 numbers converted into dB for the range of –70 dB to 18 dB, although any positive 4.20 number may be used.

To mute any of the channels, 0s are loaded into the respective mixer control register.

Mixer controls are updated instantly and can cause audible artifacts for large changes in setting when updated dynamically outside of the fast load mode; therefore, it is desirable to use fast load in conjunction with the soft-volume mode.

SDIN1, SDIN2, and the ADC output can be mixed with a user-selectable gain for each channel. The gain control registers are represented in 4.20 format.

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