highlighting specific frequencies in waves

Share icon

Thu, 05/09/2013 - 08:49 am

If I have a wave that contains multiple frequencies , how can I highlight where in the data a specific range of frequencies occur? For example, if the data has frequencies between 1 and 500Hz but I am interested in finding where frequencies from 3-5 Hz are present, how would one go about doing this? The duration of the wave is about a minute long.
Do you know how to use the FFT operation?

--
J. J. Weimer
Chemistry / Chemical & Materials Engineering, UAHuntsville

May 9, 2013 at 09:53 am - Permalink

Thanks for your suggestion.
I was able to get a magnitude vs frequency graph using this command but this is not quite what I want.I am new to signal processing so I am not quite sure if this is something trivial that can be achieved easily. Is it possible to highlight in the original wave when certain frequencies are most dominant?

May 9, 2013 at 02:20 pm - Permalink

If your data is a narrowband signal, you can calculate the instantaneous frequency (frequency vs time) (see also the example in displayhelptopic "HilbertTransform")
duplicate/o data, instantphase
hilberttransform/dest=dataH data
instantphase=atan2(data,dataH)
unwrap 2*pi, instantphase
differentiate/meth=1 instantphase /d=instantfreq
instantfreq/=2*pi


For broadband signals, one can calculate a sonogram / spectrogram (see
\WaveMetrics Procedures\Analysis\DSP (Fourier etc)\sonogram.ipf; some documentation in the procedure file itself)<br />
<br />
- Fabrizio</span>

May 9, 2013 at 03:41 pm - Permalink