### One pole filter, LP and HP

Type : Simple 1 pole LP and HP filter
References : Posted by scoofy[AT]inf[DOT]elte[DOT]hu
Notes :
Slope: 6dB/Oct

Reference: www.dspguide.com
Code :
Process loop (lowpass):
out = a0*in - b1*tmp;
tmp = out;

Simple HP version: subtract lowpass output from the input (has strange behaviour towards nyquist):
out = a0*in - b1*tmp;
tmp = out;
hp = in-out;

Coefficient calculation:
x = exp(-2.0*pi*freq/samplerate);
a0 = 1.0-x;
b1 = -x;

from : nobody[AT]nowhere[DOT]com
comment : Of course, you don't need tmp. Process loop (lowpass): out = a0*in + b1*out;

from : dj_rejo[AT]hotmail[DOT]com
comment : Why don't you just say: Process loop (lowpass): out = a0*in + b1*tmp; tmp = out; Simple HP version: subtract lowpass output from the input (has strange behaviour towards nyquist): out = a0*in + b1*tmp; tmp = out; hp = in-out; Coefficient calculation: x = exp(-2.0*pi*freq/samplerate); a0 = 1.0-x; b1 = x;

from : scoofy[AT]inf[DOT]elte[DOT]hu
comment : There's a tradition among digital filter designers that the pole coefficients have a negative sign. Of course the other one is also valid, and sometimes these notations are mixed up. If you're worried about the extra negation operation, then you could say b1 = -x; a0 = 1.0+b1; so that there's no additional operation overhead. -- peter schoffhauzer

from : scoofy[AT]inf[DOT]elte[DOT]hu
comment : Indeed.

from : bob[AT]yahoob[DOT]com
comment : Or... out += a0 * (in - out); :)

from : djdelaflav[AT]gmail[DOT]com
comment : can you please send me a few pictures to show me how you hooked up the mixer on the back...