[Eeglablist] Measurement unit of EEGlab power spectrum analysis.

[Kay Sung]

Thanks for clarification,

So, "10*log_10 (uV^2/Hz)",  is basically the log-transformed power spectral density where '/Hz' means the width of frequency bin or the minimal unit frequency being analyzed.

Now, going back to my first question, I wonder these statements are ok.

Assuming that the frequency bin size is constant within a dataset, since the power spectral density, uV^2/Hz, is another form of power measure (it is perfectly correlated with the absolute power (uV^2)), we can represent the term "10*log_10 (uV^2/Hz)" as decibel because it measure the power with respect to the unit spectral density.

Hope I'm not too wrong about this.

Thanks.

Kay Sung

>>>>>>>>>>>>>>>>>>>>>
For your second question below, the scaling is necessary to keep the power values consistent across different frequency bin widths.  If you FFT longer lengths of data, the power in any given band is split across more frequency bins.  Thus, you scale by the bin width (that's the per Hertz in the denominator) so that you can compare power values across data sets with different length FFT windows.

Hope that helps.

Cort Horton, PhD
Director of Research & Development
Qneuro Inc.  www.qneuro.com<http://www.qneuro.com>
Email: chorton at qneuro.com<mailto:chorton at qneuro.com>
[Qneuro]

Kyongje (Kay) Sung, Ph.D
Research Associate
Johns Hopkins University School of Medicine
Cognitive Neurology & Neuropsychology - Department of Neurology

1629 Thames Street, Suite 350
Baltimore, MD 21231
P 443-287-8019 | F 410-955-0188
ksung3 at jhmi.edu<mailto:ksung3 at jhmi.edu>
web.jhu.edu/cognitiveneurology/index.html<http://web.jhu.edu/cognitiveneurology/index.html>
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