musicdsp.org source code archive - WSInf

Formant filter (click this to go back to the index)
References : Posted by Alex
Code :
/*
Public source code by alex@smartelectronix.com
Simple example of implementation of formant filter
Vowelnum can be 0,1,2,3,4 A,E,I,O,U
Good for spectral rich input like saw or square
*/
//-------------------------------------------------------------VOWEL COEFFICIENTS
const double coeff[5][11]= {
{ 8.11044e-06,
8.943665402,-36.83889529,92.01697887,-154.337906,181.6233289,
-151.8651235, 89.09614114,-35.10298511,8.388101016,-0.923313471 ///A
},
{4.36215e-06,
8.90438318,-36.55179099,91.05750846,-152.422234,179.1170248, ///E
-149.6496211,87.78352223,-34.60687431,8.282228154,-0.914150747
},
{ 3.33819e-06,
8.893102966,-36.49532826,90.96543286,-152.4545478,179.4835618,
-150.315433,88.43409371,-34.98612086,8.407803364,-0.932568035 ///I
},
{1.13572e-06,
8.994734087,-37.2084849,93.22900521,-156.6929844,184.596544, ///O
-154.3755513,90.49663749,-35.58964535,8.478996281,-0.929252233
},
{4.09431e-07,
8.997322763,-37.20218544,93.11385476,-156.2530937,183.7080141, ///U
-153.2631681,89.59539726,-35.12454591,8.338655623,-0.910251753
}
};
//--------------------------------------------------------------------------------static
double memory[10]={0,0,0,0,0,0,0,0,0,0};
//--------------------------------------------------------------------------------float
formant_filter(float *in, int vowelnum)
{
res= (float) ( coeff[vowelnum][0] *in +
coeff[vowelnum][1] *memory[0] +
coeff[vowelnum][2] *memory[1] +
coeff[vowelnum][3] *memory[2] +
coeff[vowelnum][4] *memory[3] +
coeff[vowelnum][5] *memory[4] +
coeff[vowelnum][6] *memory[5] +
coeff[vowelnum][7] *memory[6] +
coeff[vowelnum][8] *memory[7] +
coeff[vowelnum][9] *memory[8] +
coeff[vowelnum][10] *memory[9] );
memory[9]= memory[8];
memory[8]= memory[7];
memory[7]= memory[6];
memory[6]= memory[5];
memory[5]= memory[4];
memory[4]= memory[3];
memory[3]= memory[2];
memory[2]= memory[1];
memory[1]= memory[0];
memory[0]=(double) res;
return res;
}
Comments
from : rhettanderson@yahoo.com
comment : Where did the coefficients come from? Do they relate to frequencies somehow? Are they male or female? Etc.
from : el98shn@ing.umu.se
comment : And are the coeffiecients for 44k1hz?
/stefancrs
from : meeloo@meeloo.net
comment : It seem to be ok at 44KHz although I get quite lot of distortion with this filter.
There are typos in the given code too, the correct version looks like this i think:
float formant_filter(float *in, int vowelnum)
{
float res= (float) ( coeff[vowelnum][0]* (*in) +
coeff[vowelnum][1] *memory[0] +
coeff[vowelnum][2] *memory[1] +
coeff[vowelnum][3] *memory[2] +
coeff[vowelnum][4] *memory[3] +
coeff[vowelnum][5] *memory[4] +
coeff[vowelnum][6] *memory[5] +
coeff[vowelnum][7] *memory[6] +
coeff[vowelnum][8] *memory[7] +
coeff[vowelnum][9] *memory[8] +
coeff[vowelnum][10] *memory[9] );