Auditory Perception

Physical Definition of Sound

Pressure changes in the air or other medium.

Perceptual Definition of Sound

The experience (i.e. sensation) we have when we hear.

Pure Tone

A tone that occurs when the change in air pressure occurs in a pattern described by a mathematical function called a sine wave.

Frequency

The number of oscillations per second, measured in Hertz (Hz).

• higher the frequency = higher the pitch for pure tones

Amplitude

The greater this is, the louder a sound seems, measured in decibels (dB). = greater air pressure greater amplitude

Complex Tones

Sounds created by combining pure tones of different frequencies.

Phons

Units of loudness for pure tones; the actual perceived loudness depending on both amplitude and frequency.

Pitch

For a pure tone, it is determined by the frequency; for a complex tone, it is usually determined by the fundamental frequency. 2 attributes tone height and chroma

• described in terms of musical notes

• notes with same letter = chroma

• as moves left to right on piano tone height increases

Chroma

Cyclic attribute of pitch, where neighboring letters of the same type (e.g., C1 and C2) sound similar.

Missing Fundamental

Complex tone will continue to repeat at the fundamental frequency, even when the fundamental frequency is absent because all other components of tone are multiples of fundamental frequency = humans perceive missing fundamental and determines pitch of complex tone

Timbre

The quality of a sound that distinguishes it from other sounds, determined by the complex overtones and harmonics present in a tone.

Periodic Sounds

Waveforms that repeat at a regular interval, such as musical sounds.

Aperiodic Sounds

Waveforms that do not repeat, such as a door slamming shut or a gunshot.

Auditory Localization

based on both binaural and monaural cues.

Binaural includes interaural time and interaural level difference

Interaural Time Difference

The time difference between when a sound reaches one ear compared to the other.

• sound from left heard by left ear first

Interaural Level Difference

The difference in sound level between the two ears, especially for high-frequency sounds due to the sound shadow.

Cone of Confusion

Any two points connected by a circumference line on the surface of a cone have the same difference in distance to the two ears = have same interaural time and level difference = binaural cues cannot be used to distinguish between the two points.

Monaural Cue for Elevation

Sound coming from different elevations bounces off different parts of the pinna before entering the ear canal = sound acquires characteristic frequency notches that depend on its elevation = used to determine elevation of sound source

Precedence Effect

If the same sound is heard twice with a temporal separation of 5-20ms, the second sound is not registered = no echo only hear direct sound. If separation between 2 sounds is more than 10th of second than will hear echo

Reverberation Time

The time it takes for sound to decrease by 60 dB

• 2 seconds for a concert hall

• 1.5 seconds for an opera hall.

Intimacy Time

The temporal difference between when the direct sound arrives and the first indirect sound arrives

• concert halls with good acoustics = intimacy time of 20 ms.

Base Ratio

Measured for the indirect sound - ratio of low frequencies to middle frequencies

• high base ratio is ideal

Spaciousness Factor

The ratio of indirect sound to total sound

• ideally want high spaciousness factor.

Cues for Separating Sound Sources

• Location - use interaural time and level differences

• Onset Time - use differences in the onset of sounds to distinguish between them (2 sounds start at different times = from different sources)

• Timbre and Pitch - use differences in timbre and pitch to differentiate sound sources.

• Auditory Continuity - ability to perceive continuous sounds in the presence of interruptions, allowing listeners to recognize a single source despite brief obstructions.

• Experience

fundamental frequency

The lowest frequency of a sound wave, determining its pitch. It serves as the primary tone from which harmonics are derived = frequency at which complex tone repeats

factors that determine quality of architectural acoustics

• reverberation time

• intimacy time

• bass ratio

• spaciousness factor