The videoclips below show spectrograms of a Mirnov coil (measuring fluctuations of the poloidal magnetic field at TJ-II). During the Neutral Beam heated phase, Alfvén modes appear, producing relatively sharply defined features in the spectrograms.
For the purpose of these clips, the fluctuations of the magnetic field have been slowed down to bring the frequencies down into the audible range.
Modulated Electron Cyclotron Resonance Heating not only modulates the electron temperature, it also modulates the rotation frequency of modes. Below is the spectrogram of a bolometry signal during ECRH modulation, showing this effect.