[R] Hidden line algorithms and a different kind of waterfall

stephen sefick ssefick at gmail.com
Sun Nov 2 20:27:09 CET 2008

this is a short time fourier transform?  Why not use wavelet
transforms that are compactly supported?  The wavelet transform
(morlet for instance) has a well know relationship between time and
scale, and doesn't rely on stationarity of the signal where as the
fourier transform does.  My signal processing skills are a little
rusty, so please correct me if I am wrong.

On Sun, Nov 2, 2008 at 10:54 AM, Carl Witthoft <carl at witthoft.com> wrote:
> Not sure what you're used to seeing, so at the risk of being redundant:
> The chart I referenced shows a series of FFTs taken over time.  The X-axis
> is frequency and the Y-axis is time (old at the top, typically).
> I used to use a similar chart to track the acoustic signatures of ships --
> you might see the peak frequency shifting over time as the ship accelerated,
> for example.
> stephen sefick wrote:
>> what is being represented here that is not on a regular spectrogram?
>> I am not being crass I can't figure out what I am looking at.  Maybe a
>> contour plot- wouldn't be in 3d but would represent the same
>> information.  I am envisioning something like a wavelet time scale
>> diagram...   Just a thought.
>> On Sat, Nov 1, 2008 at 7:11 PM, Carl Witthoft <carl at witthoft.com> wrote:
>>> This is not the same as the recent thread on a waterfall graph.
>>> I'm thinking about the rolling FFT display used in acoustics and other
>>> spectrum analysis tasks.
>>> Here's an example of a very fancy 3-D waterfall display:
>>> http://www.ultimaserial.com/UltimaWaterfall.html
>>> I was just wondering if there are any simple hidden-line tools in R that
>>> I
>>> could use to draw simple waterfall displays.  Basically, I'd like to plot
>>> a
>>> time-series of FFTs (or equivalent) and use hidden-line tools to produce
>>> a
>>> clean-looking graph.
>>> I know I could hack it using polygon() , where I'd plot c({the FFT},
>>> {line
>>> on bottom of graph}) starting at the top of the graph and working down,
>>> but
>>> wondered if there were any other tools.
>>> thanks
>>> Carl
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Stephen Sefick
Research Scientist
Southeastern Natural Sciences Academy

Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods.  We are mammals, and have not exhausted the
annoying little problems of being mammals.

								-K. Mullis

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