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| WaveWarp 2.0 Example DrawingBoard
FrequencyResponseAnalyser_2
Description
Frequency Response Analyser
Illustrates the use of the Frequency Response Analyser block for measuring the frequency response of a filter (in this
example, a 2-pole notch). The raw signal is fed into the first input of the analyser, and the filtered signal is fed into the
second input. The analyser estimates the filter's frequency response function by computing the spectra of the two signals
(using the FFT), and dividing them.
Play the Drawing Board with all Parameter Windows open (so you can see the plot windows). Note how effectively the
analyser determines the frequency response of the filter (i.e. by comparing the real-time estimate of the frequency response
in the analyser's scope window with the design response plots in the filter's window).
Try experimenting with all the settings of the analyser in order to investigate its behaviour. In particular, try switching the
FFT Window type to "None" and note the drastic reduction in the performance of the estimator compared with when the
Hanning window is used. This clearly illustrates the need for windowing. Also try varying the Averaging time of the spectrum
estimator and note that longer averaging times lead to smoother estimates.
It is also interesting to try different types of excitation signal (e.g. random noise, swept sine waves etc). Generally speaking,
it is best to use excitation signals which are rich in spectral content in order to excite all modes of the filter. In this example
of a 2-pole filter, however, almost any excitation is sufficient (for example, the drum track). Try analysing different (more
complicated) filters from the Digital Filters library -- or, for that matter, try analysing time-varying or non-linear filters (recall
that any "effect" can be considered as a "filter" so you can try and analyse its frequency response and see what
interesting results you obtain !)
Note that, at any time, you can save the estimated frequency response via the "Save spectrum to file" dialog box. You
can then analyse it off-line (e.g. in MATLAB. See the "wwxmpl11.m" script in the wwmatlab directory for an example of how
to read such files produced by WaveWarp).
Components used:
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