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Lecture 8

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  1. Lecture 8 Perceived pitch of a pure tone Absolute pitch Midterm review Instructor: David Kirkby (dkirkby@uci.edu)

  2. Miscellaneous • Results of homework #2: average score was 84%. • Homework #3 will be handed out at Tuesday’s lecture (in time for midterm review).New office hours: 10-11am, 3-4pm Wednesdays. Physics of Music, Lecture 8, D. Kirkby

  3. Review of Lecture 7 • Whether a sound is audible or not depends mostly on its intensity and frequency.Critical bands measure the size of the region of your basilar membrane that vibrates in response to a pure tone.The primary purpose of binaural hearing is to localize the source of a sound. Variations in timing (low frequency) and intensity (high frequency) are the main cues.The perceived loudness of a pure tone depends mainly on the sound pressure level, but is also affected by the sound frequency and duration. Physics of Music, Lecture 8, D. Kirkby

  4. Perception of Pitch for Pure Tones • Perceived pitch is primarily determined by the repetition rate of the air disturbance produced by a sound. • For a pure tone, this corresponds to the sound’s frequency. • For a complex musical tone, where many overtones contribute at once, the perception of pitch is more complicated: we will cover this in the next lecture. Physics of Music, Lecture 8, D. Kirkby

  5. Degrees of Pitch Perception • You can easily distinguish between musical notes (eg, A and A#) but how finely can you distinguish between subdivisions of a musical semitone (a frequency ratio of about 1 : 1.06) ?Try this demonstration of tone groups at 1000 Hz.For each pair of tones, record whether the second tone was (A) higher or (B) lower than the first tone: Source: Auditory Demonstrations, #17, Houtsma, Rossing, Wagenaars (IPO-NIU/ASA) After each group of 4 pairs, the frequency differencebetween the tones decreases. Physics of Music, Lecture 8, D. Kirkby

  6. 60 Hz 1000Hz • The correct answers are: • Group 1 10 Hz A B A A • Group 2 9 Hz A B B B • Group 3 8 Hz B A A B • Group 4 7 Hz B A A B • Group 5 6 Hz A B A B • Group 6 5 Hz A B A A • Group 7 4 Hz B B A A • Group 8 3 Hz A B A B • Group 9 2 Hz B B B A • Group 10 1 Hz B A A B Physics of Music, Lecture 8, D. Kirkby

  7. The psychophysical term for the smallest difference in sensory stimuli than can be recognized is the just-noticeable-difference (JND) or difference limen.The JND varies with thefrequency of a pure tone inthe same way as the width ofthe critical band, suggestingthat vibrations of basilarmembrane play an importantrole. Source: “The Science of Sound”, Fig 5.10,Rossing, Moore & Wheeler, 3rd ed. Physics of Music, Lecture 8, D. Kirkby

  8. An average person’s JND at 1000 Hz (the frequency used in the last demonstration) is 4-5 Hz.If you have this average ability to distinguish pitches, you got about 2 out of 4 correct starting from group 7. • The JND is about 1/30th of a critical band, or about 1/12 of a semitone above 1000 Hz. The typical hearing range is covered by about 5000 JNDs.Compare with vision: the visible spectrum is covered by about 128 JNDs. (Does this mean you can only distinguish 128 different colors?) Physics of Music, Lecture 8, D. Kirkby

  9. Perceived Pitch and Pressure Level • How does your perception of the pitch of a pure tone depend on its pressure level? • First calibrate the volume using this 200 Hz reference signal: • Next compare the pitch of the sounds in each of these 6 (quiet,loud) tone pairs of different frequencies (200, 500, 1000, 2000, 3000, 4000 Hz):Record whether the loud tone sounds higher or lower in pitch than the quiet tone, in each case. Source: Auditory Demonstrations, #12, Houtsma, Rossing, Wagenaars (IPO-NIU/ASA) Source: Auditory Demonstrations, #12, Houtsma, Rossing, Wagenaars (IPO-NIU/ASA) Physics of Music, Lecture 8, D. Kirkby

  10. High frequency True pitch Perceived Pitch Low frequency Sound Intensity • Most people find that perceived pitch increases with pressure level at high frequencies, but decreases at low frequencies. Physics of Music, Lecture 8, D. Kirkby

  11. Perceived Pitch and Sound Duration • How long does a sound have to last in order for you to identify its pitch?A single cycle of a 1000 Hz sound lasts only 1 ms, but in principle has a well-defined pitch. Is that enough? • Listen to these examples of pure tones of 300, 1000, 3000 Hz of increasing duration: 1, 2, 4, 8, 16, 32, 64, 128 cycles.How many cycles are required to establish a sense of the sound’s pitch? Source: Auditory Demonstrations, #13, Houtsma, Rossing, Wagenaars (IPO-NIU/ASA) Physics of Music, Lecture 8, D. Kirkby

  12. Absolute Pitch • Absolute pitch (or perfect pitch) is the ability to recognize or produce a particular pitch without using a reference tone.Compare with vision: most people can recognize the spectral color red. The exception are the approximately 2% of the population (mostly male) that are color blind.How many people can recognize a middle C in the same way? This is a very rare capability that less than 1 person in10,000 has. If you think you might be one of them, trythis online test: http://perfectpitch.ucsf.edu/ Physics of Music, Lecture 8, D. Kirkby

  13. Nature vs Nuture • There is no consensus yet on the origin of perfect pitch ability: is it inherited or learned or both? • Perfect pitch ability is sometimes also accompanied by synesthesia: the innate association of sounds with colors. • For more information, see: • http://perfectpitch.ucsf.edu/pppress.html#Krieger Physics of Music, Lecture 8, D. Kirkby

  14. Relative Pitch • Although few people can identify the absolute frequency of a sound, most people can identify relative pitches (i.e., musical intervals) and this ability can be improved with training.This is, in itself, a remarkable ability that we do not have for vision. Can you recognize spectral colors whose frequencies are in a specific ratio, e.g., 4:3 (a perfect fourth)?You can probably do this easily for sounds, even without any musical training. For example, start singing Auld Lang Syne: the first two notes are separated by a perfect fourth. Physics of Music, Lecture 8, D. Kirkby

  15. Summary • The perceived pitch of a pure tone depends mainly on its frequency, but also depends on the sound’s intensity and duration. • The average frequency range of hearing is covered by about 30 critical bands and about 5000 just-noticeable-differences (JNDs). • Most people perceive relative pitch quite accurately but not absolute pitch. This is in contrast to vision where most people perceive absolute frequency (color) accurately but not relative frequency. Physics of Music, Lecture 8, D. Kirkby

  16. Midterm Review • Refer to this web page (included in the handout): • http://positron.ps.uci.edu/~dkirkby/music/html/MidtermReview.php • And the sample midterm exam linked to it (also included in the handout). Physics of Music, Lecture 8, D. Kirkby