cherrie wrote:>>>> Use decibel measurements to provide relative fictitious power. For > such >> an application, using magnitude or RMS merely changes an additive >> constant. >> >> Yes... or in other words: the reference to "relative fictious power" >> becomes a scaling factor c, as in c*V^2, hence: Simply use V^2. >> >> It might be R or it might be an empirically found (constant) fudge > factor, >> as long as you don't require absolute powers. >> >> -mn >> > > Do you mean to just use V^2 to find the relative power and not dividing > this by R??There's nothing better than that when the overall system gain isn't known. There are many imponderables here. How much of the neural signal is captured by the electrodes? What is the gain of the amplifier-ADC chain? The appropriate value of R is only one of the missing pieces. It is easy to compute relative power, but it is also easy to be misled by subtleties. When comparing the power in two leads, the assumption that they have equal sensitivity really ought to be checked. When comparing powers at different frequencies in the same lead (by means of a Fourier transform or by any other frequency-separation technique) the actual frequency response of the channel must be accounted for. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Computing EEG power vs time
Started by ●October 2, 2007
Reply by ●October 3, 20072007-10-03
Reply by ●October 3, 20072007-10-03
Jerry Avins <jya@ieee.org> wrote in news:ObOdne7FpJwEP57anZ2dnUVZ_smnnZ2d@rcn.net:>> Do you mean to just use V^2 to find the relative power and not dividing >> this by R?? >Often, these things are expressed as a ratio of powers between the output and input, so the "R" cancels out. For EEG, one would assume you're interested in ratios anyway, as unless you're modeling the whole bioelectric phenomena of the head, the scalp measurements will always have unknown scale to some extent -- Scott Reverse name to reply
