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Perception of Complex Sounds- Spectral Cues.docx

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Paul Faure

November 29 , 2013 Psych 3A03: Audition Perception of Complex Sounds: Spectral Cues Periodicity Pitch - Periodicity pitch of a complex stimuli can be perceived with or without stimulus energy at F 0 Complex or Virtual Pitch - Even when no periodicity present at the period of the missing F , th0 missing F0can still be perceived Pitch Shift of the Residue (Complex Pitch) - Pitch shift of the residue - Not due to spectral energy or envelope periodicity or harmonic spacing Mechanisms of Pitch Perception - Place theory says pitch relates to excitation pattern - Different frequencies excite different places (tonotopy) - Cannot explain pitch perception because a sound of a particular pitch can be perceived even when there is no energy at the frequency corresponding to the pitch - Volley (temporal) theory says that time pattern of neural impulses determines pitch - Interval between impulses related to period of stimulus - Cannot explain pitch perception – no phase locking to stimulus frequencies above 5kHz - Pitch perception probably involves both place and volley theory Nonlinear Tones - When auditory system is stimulated at high levels with a tonal complex, Ss report hear pitches at:  Aural harmonics (2f1, 3f1)  Difference tones (f1-f2)  Cubic difference tone (2f1-f2) - These sensations reflect the nonlinear properties of the peripheral auditory system  F1 – 840; f2 = 1000Hz  Cubic difference tone: 2f1 – f2 (2 x 840) – 1000Hz = 680Hz Estimating Nonlinear Tone Level and Phase - Use cancellation method to describe the level and phase of nonlinear distortion product tones  F1 = 840 Hz; f2 = 1000Hz  Cubic difference tone = 680Hz - Play f1 + f2, subject reports hearing a itch of 680Hz, which is the cubic difference tone - Play subjects: f1 + f2 + (2f1 – f2 [180 phase shifted]) - Ask subjects to adjust level and phase of cancellation tone - Adjust until the cubic difference tone pitch of 680Hz is cancelled The Cancellation Method a) Level of cancellation tone required to cancel 680Hz cubic difference tone. Cancellation tone 5-28dB SPL yellow primary tones b) Phase of cancellation tone required to caocel 680Hz cubic difference tone (cubic difference tone phase is + 180 C) Timbre is Multidimensional - Timbre depends on more than just bandwidth (frequency spectrum) of sound - Fluctuations over time are also important - Timbre is multidimensional; no single scale along which sounds of different timbres can be ordered or compared - Temporal information is important - E.g. timbre of a piano recording is completely different when the recording is played in reverse even though long-tem spectrum is unchanged Other Sound Attributes - In addition to richness (timbre), musicians offer refer to the consonance and dissonance of complex stimuli - Musicians can play notes separated by intervals. The intervals created two categories of sound:  Intervals or sounds which are consonant are pleasing  Intervals or sounds which are dissonant are unpleasant - Sounds which are beating have the attributes of flutter and roughness as f1- f2 increases - Density is proportional to frequency and intensity - Volume is inversely proportional to frequency and proportional to intensity – thus density and volume are approximately opposites Timbre, Consonance and Dissonance - Differences in the quality of a complex tone/sound that are not described by pitch, frequency, loudness are often referred to as differences in timbre - Timbre is used to describe differences in the quality of sounds of the same pitch on different musical instruments - Another distinction between complex tones is consonance and dissonance – complex tones that sound pleasant are said to be consonant whereas unpleasant ones are dissonant Sound Localization - Perhaps the most important function of the auditory system - Important for the survival and reproduction of all hearing organisms - Sound sources must be localizable in dimensions (3D) - Sound stimulus itself has no spatial dimensions - Therefore, sound localization is the result of the auditory system’s a
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