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AEC Demonstration
To experiment with different values of echo tail length, change the EC_ECHOTAIL
constant defined in the ec_api.h include file, rebuild EC demo.mcp , reprogram
board 1 and rerun the demo application. The demo application relays the state of
operation through the LEDs and the LCD.
While the application is loading and initializing the on-chip and off-chip peripherals, a
boot screen is displayed. This is then switched to the run screen (see Figure 3-4 ).
FIGURE 3-4:
DEMONSTRATION RUN-TIME LCD SCREEN ON BOARD 1
Echo Cancellation
OnOff SW1 : Init SW4
Off : 18db NLP
* CLIPPED
The run-time screen displays the following:
1. The name of the algorithm.
2. SW1 is used to turn acoustic echo cancellation ON and OFF. SW4 is used to
reinitialize the acoustic echo cancellation algorithm.
3. The current state of the algorithm (OFF) and the NLP level selected.
4. A VU meter showing the input levels. The top bar represents the nearEndIn
buffer, the bottom bar represents the farEndIn buffer. The bands show an
acceptable input range. CLIPPED is displayed when either input signal is too large.
The amount of nonlinear processing can be increased in 6 dB steps (up to 90 dB) by
pressing SW3. It can be reduced in 6 dB steps (down to 0 dB) by pressing SW2. The
default level for most applications is 18 dB. The acoustic echo cancellation can be
reinitialized by pressing SW4.
3.1.4
Demonstration Code Description
The demonstration code runs on a dsPIC DSC device, using the Primary Oscillator as
the clock source with the PLL set for 40 MIPS operation.
The file, main.c , contains the main function for the demo application. This main
function allocates all the variables and arrays in data memory that are needed for DCI
data buffering, as well as the blocks of data memory that need to be allocated for the
AEC library functions.
The main function calls the EC_init() function from the AEC library, which initializes
the AEC algorithm to its default state.
The main function also calls the SI3000_open() function to initialize the DCI module,
the Si3000 codec and the DCI interrupt. The DCI module acts as a Master and drives
the serial clock and frame synchronization lines. The Si3000 codec acts as a Slave.
The DCI module is set for the multi-channel Frame Sync Operating mode, with 16-bit
data words and 16 data words or time slots per frame, of which only one transmit slot
and one receive slot are used in this demonstration.
Subsequently, this function initializes the Si3000 codec. The codec is reset, by
connecting the RF6 pin of the dsPIC DSC device to the Reset pin of the Si3000, holding
RF6 low for 100 cycles and then bringing it high. The codec is configured for a sample
rate of 8 kHz. The MIC Gain is set to 10 dB and the Receive Gain is set to 0 dB. Both
speakers are set to Active and the Transmit Gain is set to 0 dB. The Analog Attenuation
parameter is set to 0 dB. After initializing all of the Si3000 control registers, a delay is
introduced for calibration of the Si3000 to occur. Finally, the DCI interrupt is enabled.
? 2004-2011 Microchip Technology Inc.
DS70134F-page 25
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