Re: sosfit in filter function

[Renato S. Yamane]

2018-05-09 19:31 GMT+02:00 Mike Miller <address@hidden>:
> Instead of this
>
>     [b, a] = butter (...
>     output = filter (b, a, input);
>
> you would use this
>
>     [z, p, k] = butter (...
>     sos = zp2sos (z, p, k);
>     output = sosfilt (sos, input);

Thank you so much for your support!
Now, as it´s not possible see the response frequency of the filter
using freqz, I opened the output file in Audacity.

When the audio is very compressed (6dB Crest Factor), the response
frequency don´t keep attenuating in LOW frequencies.
See here: https://ibb.co/iQD8Ty

++++++++++++++++++++++++++++
sampling_rate = 44100;
length = 120;
hpf = 40;
lpf = 400;
filter_order = 4;
crest_factor = 6;

typenoise = noise((length)*sampling_rate, 1, 'pink');

[z, p, k] = butter(filter_order, [hpf/(sampling_rate/2),
lpf/(sampling_rate/2)]);
sos = zp2sos (z, p, k);
filtered = sosfilt(sos, typenoise);
normalized = filtered / (rms(filtered) / 10^(-crest_factor/20));

while (normalized(normalized > 1) || normalized(normalized < -1))
  normalized(normalized > 1) = 1;
  normalized(normalized < -1) = -1;
  normalized = normalized / (rms(normalized) / 10^(-crest_factor/20));
endwhile

audiowrite ('output.wav', normalized, sampling_rate);
----------------------------------------------------

Best regards,
Renato