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 Difference Threshold -- smallest detectable change in a stimulus These 2 Thresholds were the primary questions in CLASSICAL PSYCHOPHYSICS Thresholds

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

The Auditory Response Area Thresholds

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

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

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

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

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

Equal Loudness Contours: The Phon Lines Loudness/Pitch

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

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

Loudness/Pitch

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

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

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

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

Masking

Critical Bands: Fletcher Masking

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

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

Brief Sounds: Temporal Integration

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

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

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

Sound Localization Binaural

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

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

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