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Acoustics

  • H5-20: HEARING SCIENCE LABORATORY - FREQUENCY JND

    H5-20
    Demonstrate the frequency just noticeable difference and, in general, to demonstrate a large number of hearing tests as performed by clinical audiologists.
    This device can be used for over 66 different audio demonstrations and tests as described in an accompanying manual. The setup shown above is used to illustrate the just noticeable difference (JND) in frequency. Two built-in oscillators are set to very closely-spaced frequencies, and the device then produces a series of alternating tones of the two frequencies, each lasing about one-half second. As the two frequencies are separated the listener is asked to say when he or she actually can hear the difference - the frequency JND. The JND is typically about one-half percent in frequency, but becomes larger at low frequencies. See manual for a large number of other experiments. Note that due to aging of the equipment and the loss of the frequency counter, some experiments may not be functional.
    FS1

  • H5-21: THREE DECIBELS

    H5-21
    Demonstrate the logarithmic nature of dBs
    The decibel scale measures sound pressure level logarithmically against a base value. As such, a doubling of sound intensity (such as by doubling the number of approximately equivalent sound generators) creates a 3 decibel increase. This scale was developed as a result of Weber's Law: that a noticeable difference in a stimulus is an increase in a constant fraction.

    To demonstrate that doubling the sound intensity creates a change of 3 decibels in the sound intensity level: Divide the class in two, ask one half to make some noise (eg clapping), and note the sound intensity level. Then ask the whole class to make the same noise, raising the sound intensity level by 3 dB. For large groups, a camera may be provided to display the sound level meter.
    H5

  • H5-22: EFFECT OF ATTACK TRANSIENT ON TONE QUALITY OF CORNET

    H5-22
    Illustrate how attack transients strongly affect the tone quality of a musical instrument.
    Two mpeg videos, linked below, are played in succession. The first is a cornet playing the overtones of the instrument with no valves depressed. The second is the same series of notes, except that the normal attack transients have been removed by editing the source. Note the substantial difference between the apparent tone quality, or timber, of the cornet in the two audios. The wave shape of each note is shown on both oscilloscope screens, and the fundamental frequency is shown on the lower trace for the set without transients.
    H5, OS5, ME2, ME3

  • H5-31: DIPLACUSIS AND BINAURAL BEATS

    H5-31
    Demonstrate individually the phenomena of binaural beats and diplacusis.
    Two sine wave oscillators present their signals separately to the two ears using stereophones through the Diplacusis and Binaural Beat Demonstrator. Binaural beats occur in the brain when the frequencies of the two waves are very close, but the two waves do not physically mix to create first order or monaural beats. The amplitude of the two waves is kept small enough to avoid bone conduction. A subject is asked to match the pitch of the two oscillators under these circumstances, which is very difficult even for most trained musicians. Diplacusis refers to the inability to match pitches when the two tones are presented to separate ears. The two tones can be combined by flipping a switch on the Demonstrator, and the sum wave can be displayed on the oscilloscope. Several listeners can observe the proceedings through individual stereophone jacks.
    H5, ME2, ME3

  • H5-41: COMPACT DISC - AUDITORY DEMONSTRATIONS

    H5-41
    Provides a wide variety of auditory demonstrations and illusions, monaural and binaural.
    This CD has excellent content and is of the highest technical quality. Included are: (I) Frequency Analysis and Critical Bands, (II) Sound Pressure, Power, and Loudness, (III) Masking, (IV) Pitch, A. Pitch of Pure Tones, B. Pitch of Complex Tones, C. Repetition Pitch, D. Pitch Paradox, (V) Timbre, (VI) Beats, Combination Tones, Distortion, Echoes, (VII) Binaural Effects.
    H5, FS1

  • H5-42: AUDIOTAPE 24 MIN - GETTING THROUGH

    H5-42
    Demonstrate some hearing defects common to hearing impaired individuals, and to illustrate how these defects can be partially corrected using a hearing aid.
    Several types of hearing loss are illustrated on this tape and the effects of each problem are briefly discussed. Correction of the problem by a hearing aid is then illustrated, along with basic limits to electronic compensation. This tape gives the listener a good idea of the problems associated with several types of hearing loss.
    H5, FS1

  • H5-43: AUDIOTAPE 6 MIN - SHEPARD'S TONES

    H5-43
    Illustrate the audio analog to the "spiral staircase" effect.
    This tape contains stepwise upward and downward Shepard's tones.
    H5, FS1

  • H5-45: AUDIOTAPE 32 MIN - AUDITORY ILLUSIONS AND EXPTS

    H5-45
    Illustrate a variety of audio effects and illusions.
    Contents: AUDITORY BEATS IN THE BRAIN: Introduction; Changing Binaural Beats; Perception of Beat Intensities; Masking Effect of Noise; Perception of Clicks; Sound Pattern of Clicks. MUSICAL ILLUSIONS: Introduction; Two-Tone Sequence; A Simple Musical Sequence; Perception of Dissonance. MUSICAL STAIRCASE: Stepping Up; Gliding, Soaring; Explanation, Gliding.
    H5

  • H5-46: COMPACT DISC - MUSICAL ILLUSIONS AND PARADOXES

    H5-46
    Demonstrate sound illusions.
    This disc contains a variety of musical illusions, many of which must be heard using stereo headphones, but a few of which are useful in a class when played on a speaker system. Included are: (1) Introduction, (2) Octave Illusion, (3) "High-Low," (4) Scale Illusion, (5) Chromatic Illusion, (6) Glissando Illusion, (7) Tritone Paradox, and (8) Mysterious Melody. See also H5-47: COMAPCT DISC - PHANTOM WORDS & OTHER CURIOSITIES for more examples of Diana Deutsch's works.
    H5, FS1

  • H5-47: COMPACT DISC - PHANTOM WORDS AND OTHER CURIOSITIES

    H5-47
    Demonstrate audible illusions.
    This disc contains a variety of musical illusions which may be played on a speaker system. Included are: (1) Phantom Words, (2) Memory for Musical Tones, (3) Cabiata Illusion, & (4) 'But They Sometimes Behave So Strangely.' See also H5-46: MUSICAL ILLUSIONS AND PARADOXES for other examples of Diana Deutsch's work.
    H5, FS1

  • H5-48: COMPACT DISC - SHEPARD'S TONES

    H5-48
    Illustrate the audio analog to the "spiral staircase" effect.
    This CD contains a fine example of downward glissando Shepard's tones. Track 5, Fall, from "Computer Suite from Little Boy," uses downward glissando Shepard's tones to represent the dropping of the atomic bomb.
    H5, FS1

  • H5-49: McGURK EFFECT

    H5-49
    Illustrate the McGurk Effect.
    The McGurk Effect illustrates how we use visual clues as well as audible clues in interpreting speech. Click your mouse on the photograph above. Play the video a few times, watching the lips of the speaker while you listen to the audio. Then close your eyes and LISTEN only. You will notice that the speaker is saying a different syllable. This video was made with the subject saying the syllable "TAH" but the audio for the syllable "PAH" was substituted in the editing process. The "McGurk effect" was first described by Harry McGurk and John MacDonald in "Hearing lips and seeing voices", Nature 264, 746-748 (1976).

  • H6-01: FOURIER ANALYSIS OF VOICE

    H6-01
    Determine the Fourier spectrum of various steady-state spoken and sung vocal (vowel) sounds.
    An amplified microphone is fed into a digitizing oscilloscope with an FFT function. The wave shape and spectrum are displayed on screen.

    Consider inviting students with different voices up to try it out, and show how the vocal formants appear at different intonations. Compare the underlying structure to show how speech remains understandable even as formants shift.
    H6, ME2, ME3

  • H6-02: VOCAL FORMANTS

    H6-02
    Demonstrate the formant structure of different vocal sounds.
    The microphone signal is input into a TDS scope with a spectrum analyzer board, and the scope displays both the wave shape and spectrum of the input wave. Differences in the formant structure are easily observed for various vowel sounds such as (upper left to lower right) "oo," "aw," "ah," "eh," "i," and "ee."
    H2, ME2, ME3

    h6-02ah6-02gh6-02bh6-02dh6-02hh6-02e

  • H6-03: VOCAL FORMANTS - MODEL

    H6-03
    A model of vocal formants
    This short tube is closed on one end and has a sliding reed inside it, so when it is inverted the reed slides from one end to the other. (The open end is seen in the photograph at the center above, and the closed end is seen in the photograph at the right. As the air passes through the reed it vibrates, producing a fundamental frequency along with a large number of harmonics. When the reed slides toward the closed end "B" (away from the open end "A"), the vibrating air column becomes longer, so the harmonics resonated by the tube become lower in frequency while the fundamental frequency remains nearly the same. As the reed slides toward the open end "A" (away from the closed end "B"), the vibrating air column becomes shorter, so the harmonics resonated by the tube become higher in frequency while the fundamental frequency remains nearly the same.
    H6

    h6-03ah6-03b

  • H6-04: HELIUM VOICE

    H6-04
    Demonstrate the rise in frequency of vocal formants due to the increase in the speed of sound in a light gas.
    Inhale a small quantity of helium and talk and sing normally. Your voice takes on a squeaky "Donald Duck" character due to the increase in frequency of your vocal formants.

    This demonstration has the potential to be dangerous if misused, and must only be used after instruction by Lecture-Demonstration personnel. The purpose of this demonstration is to illustrate the effect of vocal formants, not as entertainment for groups where the physics content is not discussed. Take a couple of big breaths of air first to get plenty of oxygen, then breath out completely before inhaling the helium. Videos of this effect may be more useful in many classes.
    H6, FS1

  • H6-06: SYNTHESIZER - WOW

    H6-06
    Show how manipulation of formants allows a synthesizer to "talk."

    This demonstration serves to illustrate some of the concepts behind digital speech synthesis. By setting the synthesizer's oscillators and filters according to the included patch sheet, the synthesizer can be made to approximate the word "Wow."

    This is an example of formant synthesis, which creates synthetic speech by simulating individual vocal formants directly, rather than by using human-generated voice clips. This system was used by many early arcade games to generate "computer" voices, and is popularly used today in screen reader programs, as this type of synthesis is effective even at very high speeds.

  • H6-08: SOUND SPECTROGRAMS

    H6-08
    Produce audio spectrograms in the classroom
    This demonstration uses FFT software to produce sound spectrograms of the voice as well as any other sound source that can be input to the computer sound board using a 1/8 inch connector. Additional sound sources are available by request.
    FS1

  • H6-11: AUDIOTAPE 60 MIN - MUSIC OF TIBET

    H6-11
    Illustrate manipulation of vocal formants.
    Certain Tibetan monks are able to manipulate their vocal formants so that they sound like they are singing two notes at the same time. They sing a fundamental frequency of about 70 Hz, and manipulate their vocal system to produce formants at the fifth, tenth, etc. harmonics of 70 Hz. Because of this emphasis a note at 5x70Hz or 350 Hz sounds, two octaves and a major third above the fundamental.
    H6, FS1

    h6-11a

  • H6-12: AUDIOTAPE 60 MIN - THE HARMONIC CHOIR

    H6-12
    Illustrate manipulation of vocal formants and harmonics in the voice.
    Male voices sing various notes while manipulating their vocal tract to obtain emphasis on different harmonics of the fundamental note being sung. This weird phenomenon is known as harmonic singing. You have to hear it to believe it! The recording is by a group known as The Harmonic Choir, under the direction of David Hykes, based in New York City (where else if not LA?).
    H6, FS1