Fast Fourier Transform - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 242

FIGURE 6.23. ( Continued )

Example 6.9: Graphic Equalizer ( graphicEQ )

Figure 6.24 shows a listing of the program graphicEQ.c , which implements a
three-band graphic equalizer. TI's floating-point complex radix-2 FFT and IFFT
support functions are used again in this project (see also Examples 6.3, 6.4, and 6.7).
The coefficient file graphicEQcoeff.h contains three sets of coefficients;
lowpass at 1.3 kHz, bandpass between 1.3 and 2.6 kHz, and highpass at 2.6 kHz,
designed with MATLAB's function fir1 . Both the input samples and the three sets
of coefficients are transformed into the frequency domain. The filtering is performed
in the frequency domain based on the overlap-add scheme used in Example 6.7
[19,20]. Note that the complex multiplication (H)(X) , where H represents the trans-
fer function and X the input sample, yields

( ) ( ) = ( ) + ( )

H + jH X + jX H X - H X j H X + H X

R I R I RR I I RI I R

as used in the program, where
ISR continuously (every sample period T s ) outputs a value from the buffer
iobuffer , then inputs a new value until iobuffer is full. At this time a new frame

j =- 1