Mathematics and Music http://dx.doi.org/10.1090/mawrld/028 MATHEMATICAL WORLD VOLUME 28 Mathematics and Music David Wright Providence, Rhode Island 2000 Mathematics Subject Classification. Primary 00–01, 00A06. For additional informationand updates on this book, visit www.ams.org/bookpages/mawrld-28 Library of Congress Cataloging-in-Publication Data Wright,David,1949– Mathematicsandmusic/DavidWright. p.cm. —(Mathematicalworld;v.28) Includesbibliographicalreferencesandindex. ISBN978-0-8218-4873-9(alk.paper) 1.Musicalintervalsandscales. 2.Musictheory—Mathematics. I.Title. ML3809.W85 2009 781.01′51—dc22 2009014813 Copying and reprinting. Individual readers of this publication, and nonprofit libraries actingforthem,arepermittedtomakefairuseofthematerial,suchastocopyachapterforuse in teaching or research. Permission is granted to quote brief passages from this publication in reviews,providedthecustomaryacknowledgmentofthesourceisgiven. Republication,systematiccopying,ormultiplereproductionofanymaterialinthispublication is permitted only under license from the American Mathematical Society. Requests for such permissionshouldbeaddressedtotheAcquisitionsDepartment,AmericanMathematicalSociety, 201 Charles Street, Providence, Rhode Island 02904-2294 USA. Requests can also be made by [email protected]. ⃝c 2009bytheauthor. PrintedintheUnitedStatesofAmerica. ⃝∞ Thepaperusedinthisbookisacid-freeandfallswithintheguidelines establishedtoensurepermanenceanddurability. VisittheAMShomepageathttp://www.ams.org/ 10987654321 141312111009 About the Author David Wright is professor of mathematics at Washington University in St. Louis, where he currently serves as Chair of the Mathematics Depart- ment. HereceivedhisPh.D.inMathematicsfromColumbiaUniversity,New YorkCity. Aleadingresearcherinthefieldsofaffinealgebraicgeometryand polynomialautomorphisms,hehasproducedlandmarkpublicationsinthese areas and has been an invitedspeakerat numerous internationalmathemat- icsconferences. He designedand teachesa universitycourseinMathematics and Music, the notes from which formed the beginnings of this book. As a musician, David is an arranger and composer of vocal music, where hisworkoftenintegratesthecloseharmonystylecalledbarbershopharmony with jazz, blues, gospel, country, doo-wop, and contemporary a cappella. He is Associate Director of the St. Charles Ambassadors of Harmony, an award winning male chorus of 160 singers. He also serves as a musical consultant and arranger for numerous other vocal ensembles. He is active in the Barbershop Harmony Society and was inducted into its Hall of Fame in 2008. As arranger and music historian David has been featured in national radio and TV broadcasts at home and abroad and has authored several articles on vocal harmony. Contents Introduction ix 1 Basic Mathematical and Musical Concepts 1 2 Horizontal Structure 17 3 Harmony and Related Numerology 31 4 Ratios and Musical Intervals 45 5 Logarithms and Musical Intervals 53 6 Chromatic Scales 61 7 Octave Identification and Modular Arithmetic 69 8 Algebraic Properties of the Integers 85 9 The Integers as Intervals 95 10 Timbre and Periodic Functions 103 11 The Rational Numbers as Musical Intervals 123 12 Tuning the Scale to Obtain Rational Intervals 137 Bibliography 147 Index 149 vii