Faber Acoustical Forum

Faber Acoustical iOS Apps => SignalScope => Topic started by: lutz2041 on July 16, 2008, 11:52:05 PM

Title: Data window ?
Post by: lutz2041 on July 16, 2008, 11:52:05 PM
Just wanted to let you know that I have been playing with this app for a few days now. It is a little limited by the iPhones hardware, but otherwise works great. It looks great and functions very well.
I am curious however, about better explanations for the 'data window' settings under the spectrum analyzer.
What does each stand for and how does it show the signal? Maybe this is too large a task to be covered in a help file and I should go back to school..... 
Thanx for another reason to have an iPhone!!! :-D
Title: Re: Data window ?
Post by: FaberAST on July 17, 2008, 10:46:20 AM
Performing spectral analysis on a signal with the FFT (Fast Fourier Transform) requires the signal to be cut up into "chunks." The process of extracting one of those chunks is often called "windowing." It's as if you're looking at a portion of the signal through a window, and ignoring the rest of the signal. Sometimes, it's important to shape the portion of the data that lies inside the window, because it can favorably affect the result of the FFT.

The "Flat Top" window type, for example, works really well for accurately measuring the amplitude of a signal. The "Rectangular" or "Uniform" window type does not shape the data within the window at all. It offers the finest frequency resolution in the spectrum, but it may not accurately preserve the signal's amplitude at certain frequencies. There are other trade-offs associated with the various window types.

A chart of frequency-domain effects of several different window types can be found here (http://en.wikipedia.org/wiki/Image:Window_function_%28comparsion%29.png). Notice that the Rectangular and Flat Top windows lie at the extremes, in terms of frequency resolution, with everything else lying somewhere in between them.
Title: Re: Data window ?
Post by: lutz2041 on July 18, 2008, 12:21:59 AM
Thank you for the prompt reply.  That makes sense and the link was also very informative.

Thank you and keep up the great work.

P.S. Will future versions of this program have adjustments/calibrations for the microphone?