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Sound Level Meter Weighting Curve
This button shows the name of the weighting curve in use for the currently-selected channel. Clicking on the button opens the Spectrum Curves dialog to allow a different curve to be selected from among those currently loaded, or to load a new curve.
When no curve is selected for the current channel, this button shows 'Flat'.
A weighting curve is a frequency-dependent adjustment of the measured amplitude. This makes the reported SPL less sensitive to sounds in certain frequency ranges (and possibly more sensitive to others) than a simple unweighted "flat" measurement.
Typically the purpose of a particular weighting is an attempt to compensate for specific properties of human hearing. For example, humans find noise in a broad range centered around 6 kHz to be more audible and annoying than noise at lower or higher frequencies.
Suppose two sound systems have the same measured unweighted noise level when no signal is present, but one system has most of its energy in this sensitive range, while the other has it concentrated at low or high frequencies.
Human listeners would rank the first system as noisier than the second, even though both have the same overall amount of noise. Use of a weighting curve allows measured values to better correspond to actual listening experience.
Over the years, numerous weighting curves have been designated by various standards organizations for different purposes. Some curves that are intended for the same nominal purpose, such as reflecting human noise sensitivity, are actually quite different. A newer standard may make use of better understanding of human hearing, as well as better technology.
On the other hand, it may be necessary to make measurements using an older or otherwise "inferior" standard, for comparison with existing data. A manufacturer may need to provide specifications that use a particular standard, so that potential customers can make "fair" comparisons across manufacturers.
Note that in addition to a particular frequency weighting curve, a measurement standard may also specify a particular time response.
SPLcurve=1 opens the Spectrum Curves dialog, SPLcurve=0 closes it, and SPLcurve=x toggles between open and closed.
Unlike the SpectCurve command, this does not require that the Spectrum dialog already be open.
Note that you do not need to open the Curves dialog to change its controls directly via macro commands.
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