About the filtered signal

[劉彥均]

Hello , I have two question about my filtered signal .

I try to input a signal and I try to filtered it(sample= 8000 , filtered = 500-1000 Hz , band pass filter ,type : bessel filter, order=2) . After it is filtered , it's amplitude is very low.

This is my first problem : Why the amplitude of my filtered signal is very low ?

And my friend find the second problem about my filtered signal .

He said : Why there is a pulse signal in your filtered signal in the zero of time axis ?

This is my second problem : Why there is a pulse signal in your filtered signal in the zero of time axis ?

I change the frequency , amplitude , order..... , but  the amplitude is still very low , and  a pulse signal exist in filtered signal.

I try to change the another filter ,and the result is still very same.

Who can give me some suggestions?

I put the vi program and sound file under the article.

[MHawk · Accepted solution]

The energy in your file is at lower frequencies than your band-pass window and is being attenuated by the filter.

[劉彥均]

Hello , thank you for your help.

I try to filtered the signal from 10Hz to 50Hz. It is a great .

But I am very curious about  which the VI you use .

Because I use the power spectrum vi to see my power spectrum .

The result is very same, but my graph is on the time axis.

Can you give your  VI program ?

I want to know the principle .

[MHawk]

I just changed the default name of each axis on the front panel, no magic vi work. I did use a different function, FFT Power Spectrum and PSD.vi, and plotted the PSD which has units if V^2 rms / Hz instead of the V^2 rms output by Auto Power Spectrum.vi.

Be sure to wire the dt terminal of Auto Power Spectrum or it will default to a time step of 1 second, which will skew your data into appearing at a much higher frequency.

About Customizing Graphs and Charts 

[劉彥均]

I try to use the  FFT Power Spectrum and PSD.vi , but it is very weird.

So , I try to make (samples=8000 , fh= 1000 , fl=500) the same condition, and I adjust the waveform

==>

right click==>properties==>scales label==>make the x-axis 2000 multiplier , 50 offset==>

make the y-axis 0.00525 multiplier , 0.002 offset

But , the PSD graph is still not the same as yours.

May you give the vi program to me?

[劉彥均]

Can you give me your complete vi program?

I want to know why my program is weird.