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PSYCHOACOUSTICS

PSYCHOACOUSTICS. A branch of psychophysics The study of the relation between: the physical aspects of sound and the psychological experience of sound. Threshold or Limen. Absolute Threshold -- lowest value of stimulus which can be detected

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PSYCHOACOUSTICS

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  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.

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

  17. 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

  18. Masking

  19. Critical Bands: Fletcher Masking

  20. 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

  21. 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

  22. Brief Sounds: Temporal Integration Temporal Integration

  23. 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

  24. 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

  25. LOCALIZATION & LATERALIZATION LOCALIZATION: • 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

  26. Sound Localization Binaural

  27. 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

  28. 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

  29. 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

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