FIR II bit growth

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Good afternoon,

Can I please ask if there is any formula connecting the FIR II filter's performance and bit widths (especially coefficient width).

To be more precise I would like to short out (reduce) the output width that as far as I understand is determined by:input width+coefficient width+ log2(coefficient number).

I would like that as short as possible,is there any way to relate the attenuation achieved with the coefficient bit width?

Bear in mind that I simply import floating point coefficients, fixed point would increase the outoput size dramatically.

Thanks in advance,

G

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for coeffs:

convert coeffs to fixed point e.g.

coeffs = round(coeffs*2^15)/2^15;

then plot freqz(coeffs);

you should be able to see response and measure it.

for coeffs and signal:

use above scaled coeffs on fixec point input (x):

y = filter(coeffs,1,x);

f = fft(y);

plot(20*log10(abs(f)));