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Sound and vibe toolkit - third octave with windowing and overlap

Hey fancy folk,

 

I'm new to the sound and vibe stuff and I'm running into a bit of an issue.  I've would like to get A-weighted third octave data for 2 microphones, but I'd also like to window AND overlap my signal by 50%.  From my understanding, the windowing will help to get rid of the spectral spreading and the overlap will help to deal with the transient values being more accurate. 

 

 

Currently, I have my data being logged from the microphone, then being sent to an A-weighted filter, then being sent to a windowing function, then being sent to the third octave analysis. I can not figure out how to get the overlap for my data to happen.  I am working with Signal Express right now but could convert it to a VI if that is better to look at.  I have uploaded a snippet of my Signal Express... palette...? (the thing on the left side of the screen), to hopefully show whats going on.  

 

As far as I can tell, the only way to get overlap is with the Zoom FFT analysis tool.  However, that won't allow me to get the third octave bands like I'd want - well at least not easily.  From my understanding, I could go through and figure out the combo of start/stop frequencies and number of spectral lines to give me the third octave bands via Zoom FFT.  Anyways, is there an easier way to get my data to have an overlap without having to use the Zoom FFT stuff?

 

Also, I feel like my order of operations for the data is wrong.  Should I overlap the data, window the data, apply the A-weighting function, then do third octave analysis?  I'm not sure what my order should be, but I have a strange feeling that A-weighting first is wrong, but I'm fairly confident that thrid octave analysis should be last 😄

 

Matt

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Hi! I'm not an expert on DSP but can you check this link, it talks about how to select the window size and overlap.

maybe it could be useful.  Let me read and check if I can found something useful. 

 

https://dsp.stackexchange.com/questions/22175/how-should-i-select-window-size-and-overlap,

 

Have a great day.

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Alright fancy folk,

 

First, I guess I cant remember my original E-mail to log into Matt710, but this is Matt710, just re-branded :D.  

 

Second, I think I found out a way to get my data overlapped.  I was searching through some examples and I found the "SV Write to Buffer" and "SV Read from Buffer".  These Vi's will let you write the raw data to a buffer then read it with an overlap.  I basically have a consumer/producer loop set up where I'm producing my data and sending it to the "SV Write to Buffer" Vi then in the consumer loop I'm using the "SV Read from Buffer" Vi to apply the 50% overlap, then windowing, then converting to third octave data, then A-weighting.  From my understanding, A-weighting the octave (frequency) data is a lot faster than A-weighting the time data.  Can't confirm, just what I read.

 

As a heads up, the attached VI was kind of hastily made and isnt the prettiest thing I've ever created, but it gets the point across and is meant to serve as an example of how I did what I did.

 

Any who, hoping this helps someone in the future.  Hopefully I did it correctly and if not, I'm always welcome to criticism.  

Attention new LV users, NI has transitioned from being able to purchase LV out right to a subscription based model. Just a warning because LV now has a yearly subscription associated with it.
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Fancy folk,

 

I realized something with the overlap buffer read/write.  The way that I currently have my data logging is not like a FIFO buffer (the way I assumed it was).  It reads the data once, then purges the data, then collects for another X sampled (in my case ~16k samples).  I'm going to be looking into making it more like a FIFO buffer so I can keep a running Octave analysis going vs "snap shots" of the ~16k samples.

 

Matt

Attention new LV users, NI has transitioned from being able to purchase LV out right to a subscription based model. Just a warning because LV now has a yearly subscription associated with it.
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