Pitch, loudness and timbre

Pitch

A subjective sensation associated with periodic or (quasi-periodic) sounds travelling outward from a sound source. It is associated to the objective notion of frequency.

Harmonic series

Set of frequencies which are all integer multiples of the lowest, fundamental frequency (or first harmonic).

Spectrum of a periodic vibration

Harmonic series

Pattern recognition and pitch perception

When a sound is perceived, the brain searches for a pattern of harmonic frequency components. If a harmonic series is found, a single pitch is normally identified. The pitch is the same as the pitch of the fundamental.

Fusion

The fusion of frequency components gives a perception of a single pitch, even if the series is incomplete or slightly out of tune.

Frequency ratio

Two tones are separated by a pitch interval of an octave if their frequency ratio is exactly two.

Loudness

Subjective sensation related to the intensity of a perceived sound. It’s related to the objective notion of acoustic pressure. It also depends on the frequency content of the sound, because the ear is not equally sensitive to all frequencies.

Isotropic sound source

A theoretical point source of electromagnetic or sound waves which radiates the same intensity of radiation in all directions.

Loudness and sound pressure levels

Not all sounds with the same sound pressure level sound equally loud.

Equal loudness contours

A measure of sound pressure over a spectrum of frequencies that are perceived as being equally loud to the hearer when expressed as a pure, constant tone. The measurement for loudness is the ‘phon’.

Timbre

Perceived sound quality and is used to describe the specific character of a sound.

Factors of timbre

• Harmonic spectrum - same note played by different instruments can have a different form of the spectrum.

• Formants - Regions of frequency where the spectrum envelope is likely to have a peak.

• Onset transient - Built-up at the beginning of the sound, before periodic vibration sets in.