To plot the frequency curve, you need two pieces of data for each point on the curve. You need to know the frequency (which “Plot Spectrum” plots on the X axis) and the amplitude (which “Plot Spectrum” plots on the Y axis).
In the text file, the first column contains the frequency data, and the second column contains the amplitude data (in dB).
You need to import the file, using ‘space’ as a field delimiter, the data as ‘numeric’, and ‘new line’ as a ‘column delimiter’.
This should give you two columns of numeric data, the same as is in the text file.
The amplitude values are relative to a 0 dBFS sine wave.
If you want to convert from dB to linear amplitude, the equation is:
linear = 10.0 ^ (dB / 20.0)
I’m trying to do a noise analysis on a recording of patterned low frequency noise - 20Hz to 1000Hz
to find the repeating frequencies.
Did realize my error re the 2 columns after I posted.
I spliced some known frequency tones together, output and charted in Excel and got a better feel
for what I was seeing.
Per your posts I’m using the “plot spectrum” correctly with the default settings.
I’m trying enhanced autocorrelation.
Used to do dsp coding for NOAA but it was years and years ago and it’s coming
back too slowly.