Negative decibels in SpreadGIS output

[Léa Jojo]

Hello everyone,

I am using SpreadGis to modelise sound dispersion around archaeological sites, with the last version of the toolbox (4_4_2) on ArcGis 10.5.

For every model output, I used the frequency table attached, and I am getting negative decibels in each output, as shown on graphs for 1000 Hz or 400 Hz.

Do you know how to read this result?

Thanks in advance and thanks for letting everyone use this tool !

Best,

Léa

[Zorana Đorđević]

Hi,
Did someone answer this question?
I want to understand why the negative dBs occur because I have the same situation.
Thank you!
Zorana

[Sasha Keyel]

Decibels are the log of a power ratio. If the power ratio is below 1, taking the log will result in a negative value. So these are legitimate outputs.

From a practical standpoint, if they are skewing the visualization, you can use the reclassify tool in ArcGIS to reclassify these values (e.g., to make all the negatives 0, or to make anything below the environmental baseline to be the environmental baseline).

Best,

Sasha

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