Input and Output with the DSK - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 58

// Echo_control.c Echo effects with fading
//3 sliders to control effects: buffer size, amplitude, fading

#include "DSK6713_AIC23.h" //codec-DSK file support
Uint32 fs=DSK6713_AIC23_FREQ_8KHZ; //set sampling rate
short input, output;
short buffer[8000]; //max size of buffer

short bufferlength = 1000; //initial buffer size

short i = 0; //buffer index

short delay = 3; //determines size of buffer

short delay_flag = 1; //flag if buffer size changes

short amplitude = 5; //amplitude control by slider

short echo_type = 1; //1 for fading(0 with no fading)

main()
{
short new_count; //count for new buffer

comm_poll(); //init DSK, codec, McBSP

while(1) //infinite loop

{
output=input+0.1*amplitude*buffer[i];//newest + oldest samples
if (echo_type == 1) //if fading is desired

{
new_count = (i-1) % bufferlength; //previous buffer location
buffer[new_count] = output; //to store most recent output

}
output_sample(output); //output delayed sample

input = input_sample(); //newest input sample data
if (delay_flag != delay) //if delay has changed
{ //new buffer size
delay_flag = delay; //reint for future change

bufferlength = 1000*delay; //new buffer length

i = 0; //reinit buffer count

}
buffer[i] = input; //store input sample

i++; //increment buffer index

if (i == bufferlength) i=0; //if @ end of buffer reinit

}
}

FIGURE 2.17. Echo generation with controls for different effects ( echo_control.c ).

.wav file, Theforce.wav (on the CD), for input, as in Example 2.10. The output
is the sum of the newest input sample plus the oldest sample. Note that for fading,
the output is stored in the buffer.

1. Build and run this project as echo_control .
2. Access the three sliders: amplitude, delay, and type. The GEL file
echo_control.gel is shown in Figure 2.18. Set the amplitude slider to posi-