Filter related query

[Ramesh_68]

Hello, 

I am new to Labview.

I am trying to work with the sample.wav file in LV 2022. My intention is to read a .wav file and then try to apply filtering to the Sample.wav file. When I try this, while some filtering is definitely taking place, I am not sure if it working correctly (especially with the spectral measurements) With low frequency cut off set to say 350 Hhz, and high frequency cut off set to say 1200, I notice that in the frequency spectrum 370Hz and 740Hz happen to slip through.

I am attaching a screenshot of my issue along with the VI. Unfortunately I am not able to attach the sample.wav file

So what am I doing wrong? Why is the low pass filter not working?  

Any help / advice would be much appreciated and thank you in advance.

[GerdW]

Hi Ramesh,

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@Ramesh_68 wrote:

With low frequency cut off set to say 350 Hhz, and high frequency cut off set to say 1200, I notice that in the frequency spectrum 370Hz and 740Hz happen to slip through.

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You are using a 1st order filter and 370 Hz is very near to 350 Hz: what else do you expect?

[Ramesh_68]

Thank you for your response. 

What I require when i set to 350Hz is for it to function like a low pass filter permitting only those frequencies less than 350Hz.(especially with the selection set to Low pass filter)

That is not what is happenning. So how do I achieve it?

Thank you

[GerdW]

Hi Ramesh,

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@Ramesh_68 wrote:

What I require when i set to 350Hz is for it to function like a low pass filter permitting only those frequencies less than 350Hz.(especially with the selection set to Low pass filter)

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So any frequency below 350 Hz should pass, but any frequency above 350 Hz should be completely filtered?

This would be a very demanding requirement…

Have you heard any lectures on signal theory?

What do you know about applying signal filters?

Do you know each signal filter comes with (most often unwanted) side effects?

Your requirement asks for a very sharp filter: you typically want to use a high filter order.

[Ramesh_68]

Hi,

No i am not at all familiar with signal processing or filter designs. However i am willing to read up and learn.

In NI's own instructional videos on Youtube Vineeth made it so easy to use a filter (albeit with a simple sinusoidal wave). It appears I have bitten a bit more than I can chew for my maiden project.

However, that said, with my present configuration too, I find it difficult to understand why none of the frequencies about the low cut off is not attenuated. On the power spectrum, it does not even cause a dip in values 

Would be grateful if there are videos / most apt tutorials you could point me to. Notwithstanding, I will dig a bit deeper to see if i can find something.

Thank you

[Henrik_Volkers]

Another way of filtering: Do a FFT , set the unwanted frequency bins to zero,, do a invFFT ... 🙂

for big wav files maybe a challenge  ups, sometimes I forget it's 2023 and we have more than 143kB memory 😄   

[Ramesh_68]

Thank you. Let me try FFT