[sdiy] Looking for cheap lowpass filter algorithm

[Antti Huovilainen]

On Wed, 16 Aug 2006, Seb Francis wrote:

> So is there a cheap way (low CPU cycles) to implement a FIR filter with a 
> 12kHz cutoff?  It seems like there must be quick&dirty hack that will do this 
> for a frequency that is an exact power-of-2 multiple of the sampling rate.

That depends on your definition of cheap. For a DSP a FIR filter would be 
best approach. On say a dsPIC you'd use about 2*20 cycles per sample (24 
kHz sample that is) for the filtering operations.

> What about just averaging 2 consecutive samples rather than discarding 
> one of them?

Will still sound quite horrible. The stopband attenuation is just 6dB at 
16 kHz.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova