Quote:
Doug Plumb wrote:
 NASA or any other company does not ever use waterfall plots to evaluate the response of their systems and the response of their control systems is similar to what we have here. I have never seen a waterfall plot in any serious controls theory, electric circuit theory paper or in any other form. Its never used for a reason - its useless !! They are only in audio, they look pretty but mean little. A well known Phd acoustician has agreed with me on this point and doesn't use them for the same reason.
They can obfusgate the situation when people mis interpret noise or the mathematical distortions in gating as an actual physical affect, as you have above.
Every single peak in the waterfall plot is due to a peak in the frequency response. If there is a section in the waterfall that displays a decaying portion without a peak in the frequency response then its noise or some other affect.
In some non mimimum phase systems you could possibly see a decaying part that does not show as a resonance in the first slice but the resonance must appear in later slices. This is very unlikely and absolutely unlikely in a modal region room response. |
That is overstated Doug. As an example, I'm sure you have seen a great many instances where what appeared to be a single peak in the frequency response is the result of two or more modal resonances, it is only in the waterfall or by gating later parts of the impulse response that this becomes readily apparent. Whilst a waterfall plot can be misinterpreted, so can just about any other data representation - not least the frequency response itself, whose appearance in this context is entirely dependent on the window positions and durations used to generate it. It is very easy to produce frequency responses of widely varying appearance from the same impulse response. Waterfalls and similar/related data visualisations which portray combined frequency and time domain behaviour are very widely used in some fields of analysis, e.g. seismic data in oil/gas/mineral exploration.