Missing fundamental
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A missing fundamental is a missing fundamental frequency which higher frequencies refer to. For example, when a piano note has a pitch of 100 Hz, it will consist of frequency components that are all integer multiples of that value (e.g. 100, 200, 300, 400, 500.... Hz). However, low quality stereo speakers will not produce low frequencies, and so in our example, the 100 Hz component may be missing. Nevertheless, a pitch corresponding to the fundamental will still be heard. It was once thought that this was because the missing fundamental was replaced by distortions, introduced by the physics of the ear. However, experiments subsequently showed that when a noise was added, which would have masked these distortions had they been present, listeners still heard a pitch corresponding to the missing fundamental. It is now widely accepted that the brain processes the information present in the overtones to calculate what the "missing" fundamental is. The precise way in which it does so is still a matter of hot debate, but the processing seems to be based on the timing of neural impulses in the auditory nerve.
This very concept of 'missing fundamental' being reproduced based on the overtones in the tone is nowadays used to create the illusion of bass. By processing certain overtones selectively, a rich bass effect can be created using the small speakers which cannot produce lower frequency components below 100 Hz. While speakers produce tones above 100 Hz, the processed bass overtones compel the brain to replace the missing fundamental bass signals, creating the illusion of bass effect.
External links
- Pitch Paradoxical (http://www.ihear.com/Pitch/paradoxical.html)