Experiments: Pitch perception

Natural or instrumental sounds usually consist of complex harmonic structure. In this post I’ll try to explore basics of human pitch perception.

According to wikipedia: “Pitch represents the perceived fundamental frequency of a sound”. Let’s try to validate it on a simple example – sample consisting of 4 harmonics – integer multiples of 440Hz: 440Hz, 880Hz, 1320Hz, 1760Hz. Below you can find a recording of the sample repeated four times, each time followed by a single successive harmonic:

Sound followed by each of 4 harmonics

Sound followed by each of 4 harmonics

4 harmonics (Timbre file – pitch 440 with 4 harmonics)

Indeed the first harmonic – fundamental sounds with the same pitch as the whole sound. Here are more examples combined from different harmonics of the same volume, but all with the same fundamental, and thus perceived in the same pitch:

Tone variations over pitch 440

Pitch 440 variations

Pitch 440 – harmonic variations (Timbre file – pitch 440 with 32 harmonics)

So far we have observed that when the sound consist of harmonics of same volume, the first one (lowest) states about perceived pitch. So what happens if the fundamental is weaker or even missing?

Below you can hear the sequence of:

  • initial 4 harmonic sound
  • same with 1st harmonic volume set to 50%
  • same with missing 1st harmonic
  • only 1st harmonic
Pitch 440 - fundamental variations

Pitch 440 - fundamental variations

Pitch 440 – fundamental variations

Some of the population – overtone hearers – perceive the above as same pitch. Others – fundamental hearers – claims the third sound is higher then the rest. You can find out which type are you by taking this test and read about this phenomenon on wiki. My result is: 75% overtone hearer.

Resuming: on general perceived pitch corresponds to fundamental frequency (not necessarily the strongest one). When the base frequency is hidden, human mind might either try to reconstruct it from overtones or assume the lowest harmonic to be the fundamental – thus pitch perception might be undetermined.

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