DSP Robotics Support

Lets say one have a nth order (n>2) filter ... how to process it without breaking it to SOS?

Are there any ready to use implementations available (I checked quite a many examples but didn't find one (bypassed some asm listings there cause of I'm not good in reading asm code))?

SOS means second order sections aka biquads, right?
You could use a direct form like

y = b0*x + b1*x1 + ... + bn*xn;
y = y - a1*y1 - a2*y2 - ... - an*yn;

xn = xn-1;
...
x1 = x;

yn = yn-1;
...
y1 = y;

However, in single precision rounding errors will quickly make it unstable even for moderate order n. That's why we moslty use biquads.

A minor remark on why I broke the filter equation y = ... in two lines: Flowstone's code compiler has a limitation regarding the size of single line formulas it can handle. (It won`t throw an error if you exceed this limit).

OK, yes, second order sections.

I found my own SM example for biquad case:

Code: Select all

monoin inL;
monoin inR;
monoout outL;
monoout outR;

float a0, a1, a2;
float b0, b1, b2;
float inL1, inL2, inR1, inR2;
float outL1, outL2, outR1, outR2;

a0= ...
a1= ...
a2= ...
b1= ...
b2= ...

// Proces left channel
outL = a0*inL + a1*inL1 + a2*inL2 - b1*outL1 - b2*outL2;

// Process right channel
outR = a0*inR + a1*inR1 + a2*inR2 - b1*outR1 - b2*outR2;

// save previous I/Os
outL2 = outL1;
outL1 = outL;
inL2 = inL1;
inL1 = inL;

outR2 = outR1;
outR1 = outR;
inR2 = inR1;
inR1 = inR;


so, extending that would then be the way to go.