Presentation on theme: "Lecture 8 Perceived pitch of a pure tone Absolute pitch Midterm review Instructor: David Kirkby"— Presentation transcript:
Lecture 8 Perceived pitch of a pure tone Absolute pitch Midterm review Instructor: David Kirkby
Physics of Music, Lecture 8, D. Kirkby2 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. Kirkby3 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. Kirkby4 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. Kirkby5 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: After each group of 4 pairs, the frequency difference between the tones decreases. Source: Auditory Demonstrations, #17, Houtsma, Rossing, Wagenaars (IPO-NIU/ASA)
Physics of Music, Lecture 8, D. Kirkby6 The correct answers are: Group 110 HzA B A A Group 29 HzA B B B Group 38 HzB A A B Group 47 HzB A A B Group 56 HzA B A B Group 65 HzA B A A Group 74 HzB B A A Group 83 HzA B A B Group 92 HzB B B A Group 101 HzB A A B 60 Hz 1000Hz
Physics of Music, Lecture 8, D. Kirkby7 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 the frequency of a pure tone in the same way as the width of the critical band, suggesting that vibrations of basilar membrane play an important role. Source: “The Science of Sound”, Fig 5.10, Rossing, Moore & Wheeler, 3rd ed.
Physics of Music, Lecture 8, D. Kirkby8 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. Kirkby9 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. Kirkby10 Most people find that perceived pitch increases with pressure level at high frequencies, but decreases at low frequencies. Sound Intensity Perceived Pitch True pitch High frequency Low frequency
Physics of Music, Lecture 8, D. Kirkby11 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. Kirkby12 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 in 10,000 has. If you think you might be one of them, try this online test:
Physics of Music, Lecture 8, D. Kirkby13 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:
Physics of Music, Lecture 8, D. Kirkby14 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. Kirkby15 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. Kirkby16 Midterm Review Refer to this web page (included in the handout): And the sample midterm exam linked to it (also included in the handout).