lecture 10 ï‚§ musical notes and scales ï‚§ scales and timbre...
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Lecture 10 Musical Notes and Scales Scales and Timbre Pythagorean Scale Equal Temperament Scale Unorthodox Scales Instructor: David Kirkby (firstname.lastname@example.org) Slide 2 Physics of Music, Lecture 10, D. Kirkby2 Midterm The average score on the midterm was 64%. The average on the multiple choice section (73%) was higher than on the written sections (59%). This average corresponds to C+/B-, which is most likely where the final course average will end up and is normal for an intro physics course. I will be checking that the grades for the two versions are consistent, and make adjustments if necessary when calculating your final grade. Remember that the midterm contributes 25% to your final grade for the course (homework is 40%, the final is 35%). Slide 3 Physics of Music, Lecture 10, D. Kirkby3 Students Hector Aleman and Claire Dreyer should see me after class today. Here are some distributions from the midterm grades: Slide 4 Physics of Music, Lecture 10, D. Kirkby4 Drop Deadline The deadline to drop this course is Friday. For Drop Card signatures, see the Physics Undergrad Affairs Coordinator: Kirsten Lodgard email@example.com 137 MSTB Homework and midterm scores are posted on the web for your reference: http://www.physics.uci.edu/undgrad/coursescores.html Slide 5 Physics of Music, Lecture 10, D. Kirkby5 Review of Lecture 9 In the last lecture, we covered: The perception of combination tones (difference tones) Different modes of hearing (analytic/synthetic, harmonic/inharmonic) The physical basis for dissonance Theories of pitch perception (the relative importance of wavelength and frequency cues) Slide 6 Physics of Music, Lecture 10, D. Kirkby6 Why does a piano have 7 white notes and 5 black notes per octave? Slide 7 Physics of Music, Lecture 10, D. Kirkby7 Musical Scales There is an infinite continuum of possible frequencies to use in music. But, in practice, most music uses only a small (finite) number of specific frequencies. We call each of these special frequencies a musical note, and call a set of notes a musical scale. Different cultures have adopted different scales. The choice of scale is primarily aesthetic, but some aesthetic judgments are heavily influenced by physical considerations (e.g., dissonance). What can physics tell us about musical scales? Slide 8 Physics of Music, Lecture 10, D. Kirkby8 Harmonic Timbres Most musical sounds have overtones that are approximately harmonic (ie, equally spaced on a linear frequency axis). This is most likely due to a combination of two related factors: The resonant frequencies of many naturally occurring resonant systems are approximately harmonic. Your brain is optimized for listening to timbres that are approximately harmonic. Note that there are examples of naturally occurring inharmonic sounds (eg, a hand clap) but we do not perceive these as being musical. Slide 9 Physics of Music, Lecture 10, D. Kirkby9 Octaves Rule Two notes played together on instruments with harmonic timbres sound most consonant (least dissonant) when their fundamental frequencies are an exact number of octaves apart: In this sense, an octave is a special interval that we can expect will play a special role in any natural scale (although it is certainly possible to invent un-natural scales). Try this demonstration to see if you can pick out octaves. frequency Slide 10 Physics of Music, Lecture 10, D. Kirkby10 The correct answer to the octave test was #4, although most people prefer a slightly bigger octave with a frequency ratio of about 2.02:1 that corresponds to #6. This preference for slightly stretched octaves may be due to our familiarity with listening to pianos which are usually deliberately tuned to have stretched octaves (more about this in Lecture 14). Slide 11 Physics of Music, Lecture 10, D. Kirkby11 Subdividing the Octave In practice, this means that if a particular frequency is included in a scale, then all other frequencies that are an exact number of octaves above or below are also included. Therefore, choosing the set of notes to use in a scale boils down to the problem of how to subdivide an octave. Is the choice of how to subdivide an octave purely aesthetic, or are there physical considerations that prefer certain musical intervals? Slide 12 Physics of Music, Lecture 10, D. Kirkby12 Scales and Timbre The choice of a scale (subdivisions of an octave) is intimately related to the timbre of the instrument that will be playing the scale. The scale and timbre are related by dissonance: the notes of a scale should not sound unpleasant when played together. For example, most people listening to an instrument with no overtones (ie, a pure SHM sine wave) will have no preference for how to subdivide an octave (and the octave is no longer a special interval). Try these demonstrations to learn more about the connection between scales and timbre.demonstrations Slide 13 Physics of Music, Lecture 10, D. Kirkby13 However, most people listening to an instrument with harmonic timbre (ie, most musical instruments) will have a definite preference for certain intervals where overtones coincide exactly. Different instruments with harmonic timbres have different strengths for the various harmonics. These differences affect how consonant the preferred intervals are but do not change their frequencies. Therefore, there is a universal set of preferred subdivisions of the octave for instruments with harmonic timbres (based on a physical model of dissonance). Slide 14 Physics of Music, Lecture 10, D. Kirkby14 How Finely to Chop the Octave? Minimizing the dissonance of notes played together on instruments with harmonic timbres gives us some guidance on how to create a scale with a given number of notes, but not on how many notes to use. Some of the conventional choices are: Pentatonic: octave is divided into 5 notes (eg, Ancient Greek, Chinese, Celtic, Native American music) Diatonic, Modal: octave is divided into 7 notes (eg, Indian, traditional Western music) Chromatic: octave is divided into 12 notes (modern Western music) Slide 15 Physics of Music, Lecture 10, D. Kirkby15 A Primer on Musical Notation The white notes on the piano are named A,B,C,D,E,F,G. After G, we start again at A. This reflects the special role of the octave: we give two frequencies an octave apart the same note name. CDEFGABCDEFGABC Slide 16 Physics of Music, Lecture 10, D. Kirkby16 Going up in frequency (towards the right on the keyboard) from a white note to its adjacent black note gives a sharp: C goes to C #, D goes to D #, etc. Similarly, going down in frequency gives a flat: D goes to D b, E goes to E b, etc. CDEFGABCDEFGABC F#F# G#G# A#A# C#C# D#D# F#F# G#G# A#A# C#C# D#D# GbGb AbAb BbBb DbDb EbEb GbGb AbAb BbBb DbDb EbEb C # and D b are necessarily the same note on the piano, but this is not generally true for all possible scales! Slide 17 Physics of Music, Lecture 10, D. Kirkby17 Pentatonic Scales The usual choice of 5 notes in a pentatonic scale corresponds to the black notes on the piano: This scale includes the dissonant whole tone (9:8) interval, but leaves out the less dissonant major (5:4) and minor (6:5) third intervals. Why? Presumably because music limited to just 5 notes would be boring without some dissonance to create tension. Slide 18 Physics of Music, Lecture 10, D. Kirkby18 Other choices of 5 notes are also possible. Examples: Indian music Chinese music Celtic music: Auld Lange Syne, My Bonnie Lies Over the Ocean Slide 19 Physics of Music, Lecture 10, D. Kirkby19 Diatonic Scales The major and minor scales of Western music are diatonic scales, in which the octave is divided into 7 steps. The notes of the major scale correspond to the white notes on a piano, starting on C. The (natural) minor scale corresponds to the white notes starting on A. Diatonic scales can also start on any other white note of the piano. The results are the modes with names like Dorian, Phrygian, Lydian, CA Slide 20 Physics of Music, Lecture 10, D. Kirkby20 Most Western music since the 17th century is based on major and minor scales. Earlier music was primarily modal. Example: Gregorian chants Slide 21 Physics of Music, Lecture 10, D. Kirkby21 Chromatic Scales Although most Western music is based on diatonic scales, it frequently uses scales starting on several different notes in the same piece of music (as a device for adding interest and overall shape). A major scale starting on C uses only white notes on the piano, but a major scale starting on B uses all five black notes. Slide 22 Physics of Music, Lecture 10, D. Kirkby22 The main reason for adopting a chromatic scale is to be able to play pieces based on different scales with the same instrument. An octave divided into twelve notes includes all possible seven-note diatonic scales. Not all instruments adopt this strategy. For example, harmonicas are each tuned to specific diatonic scales. To play in a different key, you need a different instrument (or else to master bending techniques). What exactly should be the frequencies of the 12 notes that make up a chromatic scale? Slide 23 Physics of Music, Lecture 10, D. Kirkby23 Is there an obvious way to subdivide an octave into twelve notes? Yes: the notes should be equally spaced and include all of the special consonant frequency ratios (3:2, 4:3, ). To what extent is this actually possible? After the octave, the fifth (3:2) is the most consonant interval for harmonic timbres. The fourth (4:3) is really just a combination of the octave and fifth: 4/3 = (3/2) x (1/2) Slide 24 Physics of Music, Lecture 10, D. Kirkby24 The Circle of Fifths We can reach all 12 notes of the chromatic scale by walking up or down the piano in steps of a fifth (3:2): Going up, we reach all white notes of the piano except F, and then go through the sharps. Going down, we hit F first and then go through the flats. Either way, we eventually get back to a C (7 octaves away) if we start on a C. Slide