Frequency CodingAnd

Auditory Space Perception

Three primary dimensions of sensations associated with sounds with periodic waveforms

Pitch, loudness and timbre.

Pitch - sensation of "altitude" or "height" of a tone.

Loudness - sensation of "intensity" of a tone.

Timbre - quality of a sound.

Psychological Dimension Associated Physical Dimension

Pitch FrequencyLoudness AmplitudeTimbre Spectrum

Historically, there have been two major approaches to frequency coding.

Frequency theory (or timing) and Place theory

- both focused on the basilar membrane

Frequency Mechanisms

20 Hz

Place Mechanisms

150 Hz 20,000 Hz

4, 000 Hz

400 800 1,200 1,600 2,000 2,400

400 Hz tone plus harmonics

400 800 1,200 1,600 2,000 2,400

Harmonics only

800 1,600 2,400

800 Hz tone plus harmonics

400 800 1,200 1,600 2,000 2,400

Harmonics only

0

120

100

80

60

40

20

SP

L (d

B)

20 100 500 1000 5000 10,000

Audibilty Curve (Threshold of hearing)

Frequency (Hz)

Auditory Localization

A

B

Interaural delays for three different sound directions

Sound waves coming from the right side reach the rightear first, and there will be a large interaural delay beforethe sound propagates to the left ear.

With high frequency sound the head will cast a sound shadow

Slight asymmetries in arrival times between the two ears can be used to locate the lateral position of a stimulus. Delay lines and coincidencedetectors may perform this computation.