what started off over at linguisteresis as a simple inquiry into the difference in definition vibrato and tremolo ended up a full scale investigation.
vibrato is the fluctuation of frequency while tremolo is the fluctuation of amplitude for audio signals. vibrato seems to be more well known because it is considered a good quality to have while singing, yet tremolo is much easier to implement mathematically to a time-varying signal.
i thought a picture would be great to illustrate this difference but wikipedia surprisingly did not have an example, so i made one (seen above) and added it to the page.
im not sure i can really hear the difference between the two so i dove further in by finding a sample audio clip of a (very soprano) operatic singer and viewed her spectrogram (not innuendo.) to me it really just sounds like the sound is getting louder and softer, but what i see is clearly vibrato:
