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FFT Waterfall

FuzzMeasure's FFT Waterfall provides many controls that allow you customize the visualization to suit your needs. The FFT Waterfall provides windowing controls that are independent from those specified in the Measurement record.

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Start at Impulse Peak

Checking this box will automatically align the start of the waterfall calculation with the peak of the impulse response. The graph will display the start time as 0ms, so that reading the relative locations of decay events is much easier.

Start and Duration

The start and duration are effectively the same as those set in a Measurement Record's Analysis Window. They dictate the point where the waterfall calculates its first slice, and the duration of the decay that is shown.

FFT Length

Modifying the FFT Length in the waterfall graph will affect two aspects of the calculation of each slice:

  1. The amount of temporal (i.e. time-domain) impulse data that is used to calculate the slice
  2. The resolution—i.e., the number of points of frequency data—for each slice

While increasing the length of the FFT would be a good idea to boost the amount of data points in measurements where low-frequency data is of concern, you are also ensuring that the "decay time" that is displayed is also being increased.

Consider the following illustration:

In this example, you can see that the choice of an 8k FFT length on the right will show far more "temporal detail", which is to say that you will be able to visualize and detect very fast changes in the decay of the impulse.

However, choosing the 32k FFT buys you a sharper picture of the frequency domain - allowing you to better distinguish the individual frequencies that are contributing energy to the room in exchange for a lower-resolution picture of how quickly those energies decay.

Slice Count

This value controls the number of waterfall slices that are calculated over the duration of the waterfall. For instance, if we set a duration of 1s, a slice count of 100 will start each slice's calculation at 10ms intervals.

Tip: Higher values will produce a smoother result that better illustrates minor variations in the decay, but be aware that they consume much more CPU and RAM to calculate.
Note: The slice count is not factored into the determination of the FFT length, nor does it truncate data fed into the FFT.

Window Shape

Your choice of window shape plays a big role in the calculation of the FFT Waterfall. Unfortunately the topic of window shapes and their consequences on FFT results is far too vast for discussion in this help documentation, so their study is left as an exercise for the reader.

With that said, there is one important note to be aware of when choosing a window in FuzzMeasure. Choosing a half-sized shape will begin the calculation of each slice on the "left side" of the window, while choosing a full-sized shape (the recommended approach for most cases) will "center" the slice's start time within the window.

See the following illustration for more details: