1. PSYCHOACOUSTICS A branch of psychophysics
The study of the relation between:
the physical aspects of sound
and
the psychological experience of sound

2. Threshold or Limen
Absolute Threshold -- lowest value of stimulus which can be detected
Difference Threshold -- smallest detectable change in a stimulus
These 2 Thresholds were the primary questions in CLASSICAL PSYCHOPHYSICS
Thresholds

3. Minimum Audibility Curve--
Plot of threshold of detection (in dB SPL) as a function of frequency
Lowest thresholds in 1 to 4 kHz region
Thresholds

4. The Auditory Response Area
Thresholds

5. Auditory ResponseArea
Range of useable hearing-- from threshold of detection to threshold of feeling/pain
Also called the DYNAMIC RANGE OF HEARING
Thresholds

6. Differential Sensitivity
Detecting changes in a stimulus
(e.g., how small a change in frequency can you detect)
Measured as the jnd - just noticeable difference
Diff. Sensitivity//Weber’s Law

7. Weber’s Law--A Theory of human differential sensitivity
 S/S = k
Size of jnd = constant fraction of the stimulus you start with
It’s easier to detect small changes in a stimulus if it had a small value to begin with.
Diff. Sensitivity//Weber’s Law

8. Loudness/Pitch
Loudness--psychological experience most directly related to sound pressure/intensity
Pitch--psychological experience most directly related to frequency
Loudness/Pitch

9. Measuring Loudness:
Matching Procedure: listeners match loudness of tones at various frequencies to 1000 Hz tone -- yields unit of loudness called the PHON
Loudness/Pitch

10. Equal Loudness Contours: The Phon Lines
Loudness/Pitch

11. Measuring Loudness:
Estimation or Scaling Procedure: listeners rate tones for loudness -- yields unit called the SONE
1 sone = loudness of a sound with a loudness level of 40 phons.
2 sones are twice as loud as 1 sone.
Loudness in Sones Doubles Every 10 dB
Loudness/Pitch

12. PITCH: Place Code Periodicity Pitch Missing Fundamental Phenomenon
Loudness/Pitch

13. Loudness/Pitch

14. PITCH UNITS mel scale--The psychophysical unit of pitch
semitone - used in music; describes the ratio (16/15) in frequency between sounds. (Also used for the half step in the standard chromatic scale)
Loudness/Pitch

15. Complex Signals Sounds with energy at more than one frequency
Timbre: Sense of voice or identity: conveyed by harmonics and timing patterns.

17. MASKING
The interference with the perception of one sound produced by the presence of a second sound
Masking

18. Masking Varieties: EARS: Ipsilateral = Masker & Signal in same ear
vs. Contralateral = M in one, S in other
TIMING:
Simultaneous = M & S on at same time
vs. Forward = M precedes S
vs. Backward = M follows S
Masking

19. Masking

20. Critical Bands: Fletcher
Masking

21. Frequency Resolution
The Critical Band reflects “internal filtering”--the ability to attend to a narrow range of frequencies
Remember the tuning curves from Bekesy’s dead ear and the healthy cochlea?
You need the healthy cochlea to have good frequency resolving power

22. Good Frequency Resolution Allows you to:
Listen to harmonic structure of complex signals
Detect Shifts in Frequency (esp. formant transitions)
Hear and Understand signals in noise

23. Brief Sounds: Temporal Integration

24. Temporal Aspects: TEMPORAL INTEGRATION
A certain amount of energy must be present for detection of a brief signal.
The process of summing energy over time is called integration and it is completed by 300 ms.
If the signal is shorter than 300 ms, then power must be increased for the signal to be detected.
Temporal Integration

25. Binaural Hearing: Some Terms
AZIMUTH-angle from straight ahead in horizontal plane.
Minimum Audible Amgle- jnd for azimuth. (smallest at 0 degrees, largest near 90 and 270 deg.)
Binaural

26. LOCALIZATION & LATERALIZATION
ability to determine location of a sound source in the sound field.
LATERALIZATION:
perceived position of sound within your head for stimulation under headphones.
Binaural

27. Sound Localization
Binaural

28. LOCALIZATION CUES:
INTERAURAL TIME DIFFERENCE works best at low freqs: up to 0.65 ms at 90 deg.
INTERAURAL INTENSITY DIFFERENCE works best at high freqs: where head shadow exists.
PRECEDENCE EFFECT people can tell which ear was stimulated first.
Binaural

29. Masking Level Difference (MLD)
Masker and Signal in Each Ear
Test Threshold twice:
once with identical signals in each ear
once with 180 degrees out of phase R to L
Binaural

30. Masking Level Difference (MLD) (cont’d)
Signal is easier to detect with the interaural phase difference
Shift in threshold is about 12 to 15 dB at low frequencies.
Reflects processing in the auditory brainstem)
Binaural