Sound amplitude

[Altera_Forum]

Hi, 

I'm trying to write noise gate in vhdl. I use DE2 board and I wonder how can I compare sound amplitude and threshold in noise gate. How can I check sound amplitude value?

[Altera_Forum]

In order to estimate the sound amplitude, you can use a modified moving average filter like this: 

  y[n]=1/N*sum(k=0,k=N-1,|x[n-k]|)   This resembles a full wave rectifier.  if N=2^m you don't need any multiplier. So, you need N registers, N-1 sub/add circuits ("sub" if x[n-k]<0 and "add" if x[n-k]>=0) and a hardwired arithmetic shifter.

[Altera_Forum]

i would drop the scale factor and build this particular filter with a CIC-like structure. the actual filter becomes 2 adders (well 1 add 1 subtract). 

 input => absolute value => CIC

[Altera_Forum]

Yeah, this sounds better.