Physics
Time-Frequency Analysis
Quick fact
A standard Fourier transform shows all the frequencies present in a signal, but it loses all information about when those frequencies occur. Time-frequency analysis fixes this by letting you watch the spectrum evolve moment by moment.
Why this is interesting
You can easily see when a sound is loud or quiet on a waveform, but how do you see which note is being played at each moment—like reading a musical score from a recording?