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I am basically trying to pull frequency information and plot it according to decibels. Viewed 7k times 0 I am trying to use MATLAB to import a WAV file and create the type of diagram shown below. Ask Question Asked 10 years, 1 month ago. The only nuiance is that the article uses natural logarithms to describe the distribution and engineers like to use base 10 logarithms. Frequency : Decibel plot using FFT in MATLAB. If you compute the linear power vaiance, the you must convert to the dB domain using the method outined in the wikipedia article below. Syntax ydb mag2db (y) Description example ydb mag2db (y) expresses in decibels (dB) the magnitude measurements specified in y. Then simply converting the variance to dB (10*log10) would result in a negative variance which makes no sense. Think of it this way: Suppose you had a very tight linear distribution so that the variance (or standard deviation) was between 0 and 1. It boggles my mind as to why I can't do this. What about the std function though? If I convert the dB values to linear, compute the standard deviation, then bring it back to dB, the answer is outright wrong. See:įor an explanation of how to calculate the mean and variance. I believe what you are describing is a log-normal distribution. Standard deviation calculations were both done in dB,Įven though the distribution about the mean in dB wasn't I have encounted many radar cross-section results in theįorm of sigma ~ 30 +/- 5dB where the mean and It really depends on the application and what has been Googling for several hours has not yielded any concrete results. I'd appreciate if anyone who could shed some light on this issue. I doubt I can directly apply std() to the dB data either.ĭo I need to implement the standard deviation function manually, using x and x_bar in dB? Is there a matlab function for this?
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So, I would convert to linear, take the mean, then convert the linear mean to a dB value. It is my understanding that I cannot directly use the mean() function as the decibel values need to be converted to linear first. I'd like to get the average and standard deviation of this data between several patterns. I have a bunch of power measurements (from antennas) in dB. This is more of a fundamental mathematics question than anything.