A spectrogram unrolls sound in time: time runs to the right, frequency upwards, and colour shows how strong each frequency is. This one listens to your microphone, so you can watch your own voice while you hear it. Press Start microphone and allow access when the browser asks.
Privacy: the microphone signal is analysed locally in your browser, drawn to the screen, and immediately discarded. Nothing is recorded, stored, or sent anywhere.
What to notice: speak a slow vowel and a stack of evenly spaced harmonic lines appears; whistle and the stack collapses to a single line; hiss and you get a broadband wash with no lines at all. Then step through 64 → 128 → 256 → ... → 16384: larger windows sharpen harmonics (frequency detail) but smear rapid attacks in time, while smaller windows do the opposite.