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