Spectral Graphs

Scale

The vertical scale used to display spectral graphs may be linear or logarithmic (default). In the latter case you can set the dynamic range of display by means of adjusting the “spectral floor”, i.e. the lowest amplitude level (in decibels) displayed in graphs - use the Min list situated in the Scale group for this purpose.

The logarithmic scale is usually preferred to the linear one as it is better matched to the sensitivity characteristics of our auditory system.

NOTICE

Remember that a difference of ten decibels in the logarithmic scale is equivalent to a difference of one order of magnitude (ten times) in the linear scale.

Readings

DART XP Pro allows for precise reading of the displayed spectral plots. The value(s) of the spectral density function(s) for a particular frequency (marked with a gray vertical line), are listed in the Info window situated in the upper right corner of the graphic display. The frequency readings are provided just below the display area, inside the Spectral graph group.

In order to change the position of the frequency marker locate the pointer anywhere inside the plot area and press the left mouse button. Clicking and dragging the mouse will allow you to sweep the available frequency range (from zero to half of the sampling frequency). For fine tuning, use the right mouse button - pressing this button when the pointer is on the left/right hand side of the frequency marking line will move the line by one pixel to the left/right (which corresponds to decreasing/increasing the frequency coordinate by the (1/1024)-th part of the sampling frequency)

If you wish, you can change position of the Info window by means of dragging it and dropping to a new location. Finally, if all that you need is qualitative evaluation of spectral graphs you can remove the Info window and the frequency marker by unchecking the Info box in the Spectral graph group.

Automatic updating

When the Auto box is checked all spectral plots are automatically updated each time you change position of the cursor within a soundfile, switch between different soundfiles or modify spectrum settings. This also means that spectral graphs will be continuously updated when an active soundfile is played back.

If your computer is not fast enough, automatic updating may create some problems, e.g., skipping may occur during playback or the system may react too slowly when browsing through the soundfiles. Should anything like this happen, simply uncheck the Auto box and the plots will be redrawn only when you press the Update button.

Finally, remember to uncheck the Auto box each time you want to perform spectral analysis on a segment (block) of data.

Automatic normalization

When the Normalize box is checked the highest point of all displayed graphs is assigned the value 100% (for a linear scale) or 0 dB (for a logarithmic scale) ; the values corresponding to the remaining points are adjusted proportionally.

If you wish to compare two (or more) spectral graphs automatic normalization is not the best idea. In all such instances uncheck the Normalize box. From this point on all spectral plots will be displayed in an absolute scale - until you check the Normalize button again.

Left/right channel selection

If both channels of an active stereo soundfile are displayed, the corresponding spectral graphs are superimposed. In order to view plots for the left or right channel only, move to the toolbar and switch the LEFT/RIGHT buttons.