Re: [Signal PKG] limited slope

[Robert T. Short]

On 12/17/2017 09:48 AM, Robert T. Short wrote:
> On 12/16/2017 06:25 AM, Renato S. Yamane wrote:
> > 2017-12-15 16:34 GMT+01:00 Robert T. Short 
> > <address@hidden>:
> > > On 12/15/2017 12:27 AM, Renato S. Yamane wrote:
> > > > 2017-12-14 20:25 GMT+01:00 Robert T. Short
> > > > > On 12/13/2017 11:39 PM, Renato S. Yamane wrote:
> > > > > > Please, see the frequency response on image available in:
> > > > > > https://ibb.co/cgwOqG
> > > > > >
> > > > > > Detail: when I use a crest factor of 12dB instead 6dB, I don´t have
> > > > > > this problem.
> > > > > >
> > > > > > ==============
> > > > > > pkg load signal;
> > > > > > pkg load ltfat;
> > > > > >
> > > > > > sampling_rate = 44100;
> > > > > > lenght = 30;
> > > > > > hpf = 400;
> > > > > > lpf = 4000;
> > > > > > crest_factor = 6;
> > > > > >
> > > > > > typenoise = noise((lenght)*sampling_rate, 1, 'pink');
> > > > > > [b,a] = butter(2, [hpf/(sampling_rate/2), lpf/(sampling_rate/2)]);
> > > > > > filtered = filter(b, a, typenoise);
> > > > > > filtered = filtered / (rms(filtered) / 10^(-crest_factor/20));
> > > > > > audiowrite ('signal.wav', filtered, 44100);
> > > > > > ==============
> > > > >
> > > > > I don't get the same spectral plots you show here.  My results are 
> > > > > much
> > > > > more
> > > > > like your "expected" slope.
> > > >
> > > > Wowww!
> > > > Can you tell me how you plot it? Just to be possible I make the same
> > > > check here in my side...
> > >
> > > Well, I used a Welch's method estimator to get the spectral 
> > > density.  I used
> > > a Hamming window, but just about any window should do.  I didn't use 
> > > any
> > > overlap.  There is such an estimator as part of octave.  Then I just 
> > > plotted
> > > it.  I did a semilogx just like you did and only for frequencies > 1Hz.
> > Sorry, but can you help me with this "coding" that you did?
> >
> > Have a good day,
> > Renato
> [Tn,f] = pwelch(typenoise, hamming(2^12));
> [Fn,f] = pwelch(filtered, hamming(2^12));
>
> idx = f>0;
> figure(1);
> semilogx(f(idx),10*log10(Tn(idx)));
> figure(2);
> semilogx(f(idx),10*log10(Fn(idx)));
>
>
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If I am interpreting audiowrite correctly, it expects a max absolute 
value of unity and your signal is much greater than that.  I think you 
are clipping the snot out of the signal in the audio file.