4.10 Dynamic Range Compression/Expansion (DRCE)
The TAS3002 device provides the user with the ability to manage the dynamic range of the audio system. The DRCE receives data, and affects scaling after the volume/loudness block. As shown in Figure 4−4, the DRCE is applied after the volume/loudness control block as a DRCE scale factor. The DRCE must be adjusted such that the signal does not reach the hard limit value. However, if the signal does reach the maximum digital value, the saturation logic serves as a hard limiter that does not allow the signal to extend beyond the available range.
(Left Channel Mixer)
SDIN1_L
LEFT_SUM
SDIN2_L
ANALOGIN_L
(Parametric
Equalization)
(7)
2nd Order IIR Filters
(Tone)
Bass/ Treble
Loudness
(DRCE Scaling)
Soft
Volume/
Saturation LEFT_OUT Logic
(Analog in From ADC)
Dynamic |
Range |
Control |
ANALOGIN_R
SDIN1_R 
RIGHT_SUM
SDIN2_R
(Right Channel Mixer)
(7)
2nd Order IIR Filters
(Parametric
Equalization)
Bass/ | Soft | Saturation RIGHT_OUT |
Treble | Volume/ | Logic |
(Tone) |
| (DRCE Scaling) |
|
| |
| Loudness |
|
Figure 4−4. TAS3002 Digital Signal Processing Block Diagram
The DRCE instruction consists of eight bytes that must be sent each time in the order shown in the example code of NO TAG. Each instruction downloaded must be eight bytes. If only one byte is changed, all eight bytes must be transmitted. The first two bytes remain the same for every instruction, however the last six bytes can be programmed using hexadecimal values from the corresponding tables referred to in Section NO TAG.
With high compression ratios and fast attack times available, this function is suited for a commercial killer in a television set application.
4.11 AllPass Function
This function is enabled by setting terminal 27 (ALLPASS) on the TAS3002 device to 1. When asserted, the internal equalization filters are set into AllPass (flat) mode. When this terminal is reset to 0, the equalization filters are returned to the equalization that was in use before the terminal was asserted.
In AllPass mode, the bass and treble controls are still functional.
This function is frequently used for headphones. When the headphone plug is inserted into its jack, a switched contact in the jack enables the AllPass function.
The AllPass function also can be activated by writing a 1 to bit 2 of the analog control register.
4−6
