Jim Thomas wrote:
>           N
>   y(k) = sum x(k-n)*h(n)
>          n=0

It works! Thank you.

Cristiano

Jim Thomas wrote:
>         N
> y(k) = sum x(n-k)*h(n)
>        n=0
> 

Oops!  I reversed the n and k.  Try this instead:

          N
  y(k) = sum x(k-n)*h(n)
         n=0

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com          (703) 779-7770
Better to ask a stupid question than to make a stupid mistake.

Cristiano wrote:
> In that page I only seen the filter design, but as I said, I need to know
> how to convolve the input signal and the filter kernel.

         N
y(k) = sum x(n-k)*h(n)
        n=0

For various implementations, go to dspguru.com and read the FIR FAQ.

-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com          (703) 779-7770
Better to ask a stupid question than to make a stupid mistake.

axlq wrote:
> In article <D3wQc.76974$OR2.4340761@news3.tin.it>,
> Cristiano <cristiano.pi@NSquipo.it> wrote:
>> I'm trying to write (in C++) a low-pass filter for audio frequencies.
>
> This may help:
>
> http://unicorn.us.com/alex/buttercrit.html

In that page I only seen the filter design, but as I said, I need to know
how to convolve the input signal and the filter kernel.

Cristiano

In article <D3wQc.76974$OR2.4340761@news3.tin.it>,
Cristiano <cristiano.pi@NSquipo.it> wrote:
>I'm trying to write (in C++) a low-pass filter for audio frequencies.

This may help:

http://unicorn.us.com/alex/buttercrit.html

-A

I'm trying to write (in C++) a low-pass filter for audio frequencies.

I used this:
 H[i]= sin(2*PI*FC * (i-M/2)) / (i-M/2) *
    * 0.54 - 0.46*cos(2*PI*i/M)
where M= 100 points and FC is the cutoff frequency (0 to 0.5), but I guess I
don't know how to use it because the filtered music is really bad.

I have the real and the imaginary part of the transformed input signal.
Could anybody tell me how to convolve the input signal and the filter kernel
H[]?

Thanks
Cristiano