What is missing fundamental?

The missing fundamental is a psychoacoustic phenomenon in which the human ear perceives a tone at the lowest frequency of a harmonic series, even if that frequency is not physically present in the sound wave. This perception is generated by the brain's ability to group the harmonics of a sound wave into a single perceptual entity.

For example, if you play a note that has a fundamental frequency of 100 Hz, the harmonics of that note will be at 200 Hz, 300 Hz, 400 Hz, etc. However, if you remove the fundamental frequency and just play the harmonics, the human ear will still perceive a tone at 100 Hz.

This phenomenon has been studied extensively in the field of psychoacoustics and is widely used in music production and sound engineering. It is also used in audio signal processing algorithms, such as harmonic distortion and synthesis.