Thread: C question

Hi,

Im trying to convert from C to MATLAB.

Im a bit stuck with the following code. I need to know what is returned in OverallGainFilter?? This parameter is used elsewhere in the program.


(1) Call the function:

Code:

float   overallGainFilter = interpolate ((float) 1000, filter_curve_db, number_of_points);

filter_curve_db is a 26 by 2 matrix;
number_of_points=26;

(2) The function (interpolation):

Code:

float interpolate (float    freq, 
                   double   filter_curve_db [][2],
                   int      number_of_points) {
    double  result;
    int     i;
    double  freqLow, freqHigh;
    double  curveLow, curveHigh;
	
    
    if (freq <= filter_curve_db [0][0]) {
        freqLow = filter_curve_db [0][0];
        curveLow = filter_curve_db [0][1];
        freqHigh = filter_curve_db [1][0];
        curveHigh = filter_curve_db [1][1];
        result = ((freq - freqLow) * curveHigh + (freqHigh - freq) * curveLow)/ (freqHigh - freqLow);
		return (float) result;
    }

    if (freq >= filter_curve_db [number_of_points-1][0]) {
        freqLow = filter_curve_db [number_of_points-2][0];
        curveLow = filter_curve_db [number_of_points-2][1];
        freqHigh = filter_curve_db [number_of_points-1][0];
        curveHigh = filter_curve_db [number_of_points-1][1];
        result = ((freq - freqLow) * curveHigh + (freqHigh - freq) * curveLow)/ (freqHigh - freqLow);
		return (float) result;
    }
        
    i = 1;
    freqHigh = filter_curve_db [i][0];
    while (freqHigh < freq) {
        i++;
        freqHigh = filter_curve_db [i][0];    
    }
    curveHigh = filter_curve_db [i][1];

    freqLow = filter_curve_db [i-1][0];
    curveLow = filter_curve_db [i-1][1];

    result = ((freq - freqLow) * curveHigh + (freqHigh - freq) * curveLow)/ (freqHigh - freqLow);
	
	
	return (float) result;

}

Can anyone tell me what is returned in overallGainFilter??

Thanks for any help.

Originally Posted by quzah

My guess is a floating point number.


Quzah.

And snow is usually white.

Does anyone else have an idea what exactly is returned to overallGainFilter /how it is altered by function?

Thanks for any help.

Could it possibly be returning decibels???

The logic looks like it some sort of variant to calculate the gain of a filter as a function of frequency.