15 Chapter 2. Meeting 2, Foundations: The Science and Visualization of Sound 2.1. Announcements • Check course notes for reading and listening discussion leaders • We will cover the basics of using PD and Martingale during Meeting 5, next week 2.2. Reading: Sousa • Sousa, J. P. 1993. “Machine Songs IV: The Menace of Mechanical Music.” Computer Music Journal 17(1): 14-18. • What technologies is Sousa concerned about? • What does Sousa claim are the detriments? What is being lost? • What other causes, ignored by Sousa, might lead to the conditions he describes? • Sousa suggest that the goal of music is the “expression of soul states”; is this true? • What generalities does Sousa suggest about American music, and the history of music? • For Sousa, can mechanically reproduced music have expression? • Did copyright law, during this period, see recordings as a copy of a musical work? Why or why not? • Dose Sousa attribute agency to machines? Why is this relevant? 2.3. Listening: Young • La Monte Young: “Excerpt 31 | 69 c. 12:17:33-12:25:33 PM NYC” & “31 | 69 C. 12:17:33-12:24:33 PM NYC” • What are we hearing, and how is it made? • Is the timbre constant; when does it change?16 • What sort of performance context might this work within? • What affect does this music have on the audience? What is the role of the listener? 2.4. The Science of Sound • The attributes and measurements of sounds • How we visualize and display these attributes • How these measurements relate to human hearing and the brain: psychoacoustics 2.5. Relevance to the Study of Music and Technology • To describe and understand the abilities of various technologies • To measure technological progress or decline • To compare products and evaluate claims • To measure the efficacy of various technologies for humans 2.6. What Is Sound? • Variations in pressure through a medium• A disturbance in equilibrium • Vibration: special kind of disturbance • Vibration: an oscillating disturbance in an elastic medium 2.7. Oscillation: The Simplest Case • Oscillation is the natural motion of many physical objects disturbed from equilibrium 17 Image: "Sinusoidal pressure waves" from Sound for music technology: an introduction.http://openlearn.open.ac.uk/mod/resource/view.php?id=285732.(c) The Open University.SpringFour types of vibrating objects: simple pendulum, spring pendulum, vibrating strip,and tuning fork. 18 • Oscillation is a back and forth motion (up and down) over time • Pendulums (Swings) • Strings • A natural point of oscillation in an object is a resonance • Perfect oscillations are periodic • Perfect oscillations are impossible in nature • Noise breaks perfection: damping, friction, resistance 2.8. An Artificial Case: Perfect Oscillation • A sine wave is a perfect oscillation • An unraveled circle; back and forth over time Figure by MIT OpenCourseWare.Figure by MIT OpenCourseWare.+ a- aPositions of a vibrating mass at equal time intervals.AC0AC0m 19 • No damping or resistance • No noise • Machine-made • With machines, other shapes can be perfectly oscillated [demo/signalWaveforms.pd] Figure by MIT OpenCourseWare.20 • Sine wave: a circular oscillation • Square (rectangle) wave • Triangle wave • Sawtooth wave • When things oscillate, humans hear a tone • The shape of the oscillation makes a difference in the quality of the tone • The sine wave has advantages • It is easy to generate mechanically and mathematically • It resembles natural resonances in physical objects (simple harmonic motion) • It sounds as a simple, single isolated tone • An excellent point of oscillation (frequency) reference21 2.9. Measuring: Time • Sound requires time • Measured in seconds • 1 millisecond is equal to .001 second • 1 second is equal to 1000 milliseconds • The ear can hear discrete time intervals down to about 30 milliseconds [demo/earLimits.pd] 2.10. Measuring a Sine Wave: How Often? • How often it oscillates: its frequency • Measured in Cycles Per Second (CPS) or Hertz • Measure from crest to crest, or one period • Low frequencies correlate to what we call “low” sounds; high frequencies correlate to what we call “high” sounds • Frequency is similar to pitch, but not the same • An octave, or a frequency ratio of 2:1, is a fundamental unit of pitch • Ideal frequency range of the human ear: 20 to 20,000 Hertz • Piano keyboard: 8 octaves: A0 (27 Hz) to C8 (4186 Hz) • Audible range: 10 octaves: 20 to 20000 Hz [demo/earLimits.pd] 2.11. Frequency and Time • Frequency is a another way of specifying a duration • 1 Hz means is a cycle with duration of 1000 ms • 0.5 Hz is a duration of 2000 ms • 440 Hz is a duration of 2.27273 ms • Milliseconds and frequency can be converted each way22 2.12. Our Ear Hears Logarithmically: Pitch • Octave: an equal unit of perceived pitch, a 2:1 ratio of frequencies • Octaves are frequently divided into 12 half steps (or semitones) • MIDI pitch values provide a numerical reference to pitch (where middle C is 60 and half-steps are integers) • A change from 55 to 110 Hz (a difference of 55 Hz) sounds the same to our ear as a change from 1760 to 3520 Hz (a difference of 1760 Hz) [demo/earLogFrequency.pd]23 Courtesy of Tom Irvine. Used with permission.24 • 10 octaves of the audible frequency range: 20-40 Hz 40-80 Hz 80-160 Hz 160-320 Hz 320-640 Hz 640-1280 Hz 1280-2560 Hz 2560-5120 Hz 5120-10240 Hz 10240-20480 Hz • Frequency domain graphs often use a logarithmic graph of frequencyFigure © Routledge. All rights reserved.This content is excluded from our Creative Commons license.For more information, see http://ocw.mit.edu/fairuse.2.13. Measuring a Sine Wave: Where? • Phase refers to position or offset within oscillation or wave shape • Only meaningful in relation to a reference point or another wave • Often measured between -1 and 1, 0 to 360 degrees, or 0 to 2 π"radians"•" 180"degrees"is"one"half‐cycle"out"of"phase"•" Flipping"the"phase"is"multiplying"a"signal"times"‐1"•"shape"timbreThe"combination"of"signals"in"and"out"of"phase"is"frequently"used"as"a"creative""way"to"2•".1How"large"are"the"oscillations:"its"amplitude4.%Measuring%a%Sine%Wave :%H o w"%Much?% 2526 •" A"non‐linear"measure"in"relation"to"power"