Time frequency tutorial
Time frequency decompostions
Time frequency decomposition are a central part of EEG data analysis. In this section, we will review the basic and also some more advanced features of time frequency decompositions. The function that computes time-frequency decomposition, has about a 100 different parameters.
There are standard range of frequencies in human that have been designated using specific names.
Note that these frequencies are never present as sinosoids in actual EEG data. Instead, we most often always observe a mixture of such frequencies.
Actual EEG signal can be seen as a mixture of different frequencies. As shown below, when mixing 2Hz, 10Hz, and 20Hz signals, a complex signal may be observed.
If we run a simple Fourier Transform on this data (we will see later in this document what is actually a Fourrier Transform), then we will be able to observe 3 peaks of the same amplitude at 2, 10 and 20 Hz.
Now, if we take a real EEG signal, it is possible to decompose such signal into a superposition of signal at different sinusoidal signal at different frequencies. Note that not only the amplitude of such sinoisoid but also their "phase" (the horizontal offset).