# Spectral slope

## Homework Statement

I have some registration of sound gathered by hydrophone. Next I have created a power spectral density (dB re 1 Pa^2/Hz) vs frequency plot (semilog in matlab). And now I want to find spectral slope in dB/octave (one octave is log2(f2/f1).
I suppose that I should calculate the difference between two PSD points (max and min) and then divide this value by amount of octaves estimated based on the mentioned formula?
Could you if I'm right? Or mby there should use some different formula?

## The Attempt at a Solution

NascentOxygen
Staff Emeritus
Semilog....and your horizontal axis is f or log(f/fo)?

One actave is a doubling in frequency. So if linear f can you draw a straight line approximation to any region of interest, then extend that line over an exact octave and read the change in dB.

Drawing by hand has inherent noise-averaging, in comparison with a two points reliance which does not.

Here is an example
https://i.imgsafe.org/b3c770eb73.png [Broken]

Last edited by a moderator:
NascentOxygen
Staff Emeritus
Are you looking for a fixed dB/oct figure? If so, you will be looking for a straight line best fit to this.

Ok, so for that I must count the difference value of dB i.e. from 1 Hz - 1.5 Hz and then calculate the amount of decades from taken frequencies?

NascentOxygen
Staff Emeritus