Hearing
The subjective human response to sound.
Background Noise
The ability to hold a conversation depends on the background noise level and the distance between the people.
- 1 dB deviation per critical band is noticeable in direct comparison. Even smaller deviations can be picked up by trained listeners.
- +/-3-5dB deviations are not easy to perceive when there is no immediate reference, except for trained listeners.
- Group delay differences of roughly 1ms are noticed in extreme cases.
- Group delay differences of about 2ms become noticeable in listening tests. This equates to approximately 70cm difference in propagation length.
- 5 to 10ms group delay differences may be disturbing, however, 50 to 100ms group delay errors are tolerable depending on signal type.
Phase and Time Difference
- The auditory system is relatively insensitive to phase (Helmholtz) in general: magnitude spectrum more important than phase spectrum, but sometimes phase is important
- Phase functions from Fourier analysis are circular and difficult to analyze and interpret
- Group delay (phase derivative) is a relatively good perceptual measure which describes the delay of modulation (not the carrier).
Phase in audio reproduction:
- Group delay differences of about 1 ms are noticed in extreme cases
- Group delay differences of about 2 ms become notibeable in critical listening (about 60 cm of propagation distance difference)
- 5-10 ms group delay differences may start to be disturbing
- Even 50-100 ms group delay errors may be tolerable sometimes
- In spatial sound perception: precedence effect
Temporal Fluctuations
It is known that the temporal resolution of the auditory system is frequency dependent (Shailer and Moore, 1983, 1987). Time constants (i.e., integration times) for the lower frequency bands are larger than those for the higher bands.
| Frequency (Hz) | Gap (ms) |
| 100 | 18 |
| 200 | 9.5 |
| 400 | 7 |
| 800 | 6.5 |
| 1000 | 6 |
| 2000 | 6 |
| 3000 | 4.5 |
| 4000 | 4 |
| 5000 | 4 |
| 7000 | 3.9 |
| 8000 | 3.7 |
The gap length in ms at a characteristic frequency taken from Moore (1997)
Reference
Moore, B. C. (1997). An Introduction to the Psychology of Hearing, fourth edition, Academic Press (London).
Shailer, M. J., and Moore, B. C. (1983). "Gap detection as a function of frequency, bandwidth, and level," J.Acoust.Soc.Am. 74, 467-473.
Shailer, M. J., and Moore, B. C. (1987). "Gap detection and the auditory filter: phase effects using sinusoidal stimuli," J.Acoust.Soc.Am. 81, 1110-1117.
See also: Acoustic Source Location, Audiogram, Audiometer, Duplex Theory of Localization, Ear, Fletcher-Munson Curves, Haas Effect, Hearing Damage, Hearing Protector, Hearing Range in Animals, Interaural Cross-Correlation Coefficient, Knudson′s Law, Noise Exposure Limits, Noise Reduction Rating, Otologist, Smell, Sonic, Sound, Temporary Threshold Shift, Threshold of Hearing, Weber-Fechner Law.
Subjects: Medical Noise & Vibration