New Techniques for Enhanced Quality of Computer Accompaniment

NewTechniquesforEnhancedQualityofComputerAccompanimentRogerB.Dannenb ergScho ol ofComputer ScienceCarnegie Mellon UniversityPittsburgh, PA 15213USAHirofumi MukainoTheYamaha Corp orationHamamatsu, JAPANAbstractAcomputeraccompanimentsystemhasb eenex-tended with several techniques to solve problems as-so ciatedwithreliablyrecognizingandfollowingareal-time p erformance.Onetechniqueistheuseofan additional matcher to consider alternativeswhenthep erformancecouldb einterpretedtwoays.Another is to delay corrective action when data fromthematcher is susp ect.Metho ds for handling gracenotes,trills,andglissandiarealsopresented.Theimplementation of these and other techniques to pro-ducean enhancedcomputer accompanimentsystemis discussed.1.Intro ductionThebasictechnologyforreal-timecomputeraccompaniment1of live musicians was rst presen tedin 1984 [1, 2], however the rstsystems left a lot ofro om for improvement.We hae b een developing newcomputer accompaniment systems for two years in ane ort to obtain higher reliability in the accompanistand also to deal with a more complete musical vo cab-ulary.Like the rst systems, the task is to acceptascoredescribingmusicto b e p erformed by a humanand machine.The machine listens to the human p er-formance and synchronizes to it in real time.A variety of techniques have b een develop ed to in-0Published as: Dannenb erg and Mukaino, \New Techniquesfor Enhanced Quality of Computer Accompaniment," inPro-cedingsoftheInternationalComputerMusicConferenc,Computer Music Asso ciation, (Septemb er 1988), pp 243-249.P.S. If you know how to prop erly attach a fo otnote to a title,please let me know. -rb d@cs.cmu.edu1Computer accompaniment is the sub ject of a U.S. patent.creaseaccompaniment reliability.An important im-provementhasb eentheuseofalimited amounnon-determinism orparallelism toallowthesystemto follow two competing hyp otheses until one is seento b esup erior.A secondtechniqueis todelayout-put from the matcher in order to create a short timewindow during which decisions can b e reversed.Eventraditional scores are not completely sp eci ed and wehave incorp orated several extensionsto our matchertodealwithgracenotes,trills,andglissandi.Weindicatetheornamentationin thescoresothatsystem can have an exp ectation b efore the ornamentisp erformed.Theinputpro cessedaccordingtoexp ectations.In this pap er, we will describ e the structure and im-plementation details of an advanced p olyphonic com-puter accompaniment system.To b egin with, in Sec-tion2,wewillshothereaderbasicstructureofthisaccompanimentsystemandintro ducesometerminology.InSection3,wedescrib ehoim-plementnon-deterministicmatching.TheninSec-tion4,weshohoornamentationssuchastrillsor glissandi are handled.In Section 5, we explain theidea of delayed decision making. Finally, in Section 6,we will describ e miscellaneous improvements we haedone.2.Basic StructureIn this section, we presen t the basic structureof ouraccompanimentsystem.Wewilldescrib eonlythefundamentalideasofaccompanimentsystemshere.For more details, see the previous pap ers [1, 3].Forconvenience,wewill rstde nesometerms.Beforestartingap erformance,scoreisreadintothe system.The scorehas two parts,thesoloscore1