The MIDI Specification文档格式.docx
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wrongdirection"
asmoredevicesaredaisy-chainedtootherdevice'
sMIDITHRUjacks.Theresultisthatthereisalimittothenumberofdevicesthatcanbedaisy-chained.
Messages
TheMIDIprotocolismadeupofmessages.Amessageconsistsofastring（ie,series）of8-bitbytes.MIDIhasmanysuchdefinedmessages.Somemessagesconsistofonly1byte.Othermessageshave2bytes.Stillothershave3bytes.OnetypeofMIDImessagecanevenhaveanunlimitednumberofbytes.TheonethingthatallmessageshaveincommonisthatthefirstbyteofthemessageistheStatusbyte.Thisisaspecialbytebecauseit'
stheonlybytethathasbit#7set.Anyotherfollowingbytesinthatmessagewillnothavebit#7set.So,youcanalwaysdetectthestartaMIDImessagebecausethat'
swhenyoureceiveabytewithbit#7set.ThiswillbeaStatusbyteintherange0x80to0xFF.Theremainingbytesofthemessage（ie,thedatabytes,ifany）willbeintherange0x00to0x7F.
TheStatusbytesof0x80to0xEFareformessagesthatcanbebroadcastonanyoneofthe16MIDIchannels.Becauseofthis,thesearecalledVoicemessages.（MyownpreferenceistosaythatthesemessagesbelongintheVoiceCategory）.FortheseStatusbytes,youbreakupthe8-bitbyteinto24-bitnibbles.Forexample,aStatusbyteof0x92canbebrokenupinto2nibbleswithvaluesof9（highnibble）and2（lownibble）.ThehighnibbletellsyouwhattypeofMIDImessagethisis.Herearethepossiblevaluesforthehighnibble,andwhattypeofVoiceCategorymessageeachrepresents:
8=NoteOff
9=NoteOn
A=AfterTouch（ie,keypressure）
B=ControlChange
C=Program（patch）change
D=ChannelPressure
E=PitchWheel
So,forourexamplestatusof0x92,weseethatitsmessagetypeisNoteOn（ie,thehighnibbleis9）.What'
sthelownibbleof2mean?
ThismeansthatthemessageisonMIDIchannel2.Thereare16possible（logical）MIDIchannels,with0beingthefirst.So,thismessageisaNoteOnonchannel2.WhatstatusbytewouldspecifyaProgramChangeonchannel0?
ThehighnibblewouldneedtobeCforaProgramChangetypeofmessage,andthelownibblewouldneedtobe0forchannel0.Thus,thestatusbytewouldbe0xC0.HowaboutaProgramChangeonchannel15（ie,thelastMIDIchannel）.Again,thehighnibblewouldbeC,butthelownibblewouldbeF（ie,thehexademicaldigitfor15）.Thus,thestatuswouldbe0xCF.
NOTE:
AlthoughtheMIDIStatusbytecountsthe16MIDIchannelsasnumbers0toF（ie,15）,allMIDIgear（includingcomputersoftware）displaysachannelnumbertothemusicianas1to16.So,aStatusbytesentonMIDIchannel0isconsideredtobeon"
channel1"
asfarasthemusicianisconcerned.Thisdiscrepancybetweenthestatusbyte'
schannelnumber,andwhatchannelthemusician"
believes"
thataMIDImessageison,isacceptedbecausemosthumansstartcountingthingsfrom1,ratherthan0.
TheStatusbytesof0xF0to0xFFareformessagesthataren'
tonanyparticularchannel（andthereforealldaisy-chainedMIDIdevicesalwayscan"
hear"
andchoosetoactuponthesemessages.ContrastthiswiththeVoiceCategorymessages,whereaMIDIdevicecanbesettorespondtothoseMIDImessagesonlyonaspecifiedchannel）.ThesestatusbytesareusedformessagesthatcarryinformationofinteresttoallMIDIdevices,suchassyncronizingallplaybackdevicestoaparticulartime.（Bycontrast,VoiceCategorymessagesdealwiththeindividualmusicalpartsthateachinstrumentmightplay,sothechannelnibbleschemeallowsadevicetorespondtoitsownMIDIchannelwhileignoringtheVoiceCategorymessagesintendedforanotherdeviceonanotherchannel）.
Thesestatusbytesarefurtherdividedintotwocatagories.Statusbytesof0xF0to0xF7arecalledSystemCommonmessages.Statusbytesof0xF8to0xFFarecalledSystemRealtimemessages.Theimplicationsofsuchwillbediscussedlater.
Actually,certainStatusbyteswithinthisrangearenotdefinedbytheMIDIspectodate,andarereservedforfutureuse.Forexample,Statusbytesof0xF4,0xF5,0xF9,and0xFDarenotused.IfaMIDIdeviceeverreceivessuchaStatus,itshouldignorethatmessage.SeeIgnoringMIDIMessages.
Whatfollowsisadescriptionofeachmessagetype.Thedescriptiontellswhatthemessagedoes,whatitsstatusbyteis,andwhetherithasanysubsequentdatabytesandwhatinformationthosecarry.Generally,thesedescriptionstaketheviewofadevicereceivingsuchmessages（ie,whatthedevicewouldtypicallybeexpectedtodowhenreceivingparticularmessages）.Whenapplicable,remarksaboutadevicethattransmitssuchmessagesmaybemade.
NoteOff
Category:
Voice
Purpose
Indicatesthataparticularnoteshouldbereleased.Essentially,thismeansthatthenotestopssounding,butsomepatchesmighthavealongVCAreleasetimethatneedstoslowlyfadethesoundout.Additionally,thedevice'
sHoldPedalcontrollermaybeon,inwhichcasethenote'
sreleaseispostponeduntiltheHoldPedalisreleased.Inanyevent,thismessageeithercausestheVCAtomoveintothereleasestage,oriftheHoldPedalison,indicatesthatthenoteshouldbereleased（bythedeviceautomatically）whentheHoldPedalisturnedoff.IfthedeviceisaMultiTimbralunit,theneachoneofitsPartsmayrespondtoNoteOffsonitsownchannel.ThePartthatrespondstoaparticularNoteOffmessageistheoneassignedtothemessage'
sMIDIchannel.
Status
0x80to0x8FwherethelownibbleistheMIDIchannel.
Data
TwodatabytesfollowtheStatus.
Thefirstdataisthenotenumber.Thereare128possiblenotesonaMIDIdevice,numbered0to127（whereMiddleCisnotenumber60）.Thisindicateswhichnoteshouldbereleased.
Theseconddatabyteisthevelocity,avaluefrom0to127.Thisindicateshowquicklythenoteshouldbereleased（where127isthefastest）.It'
suptoaMIDIdevicehowitusesvelocityinformation.OftenvelocitywillbeusedtotailortheVCAreleasetime.MIDIdevicesthatcangenerateNoteOffmessages,butdon'
timplementvelocityfeatures,willtransmitNoteOffmessageswithapresetvelocityof64.
Errata
AnAllNotesOffcontrollermessagecanbeusedtoturnoffallnotesforwhichadevicereceivedNoteOnmessages（withouthavingreceivedrespectiveNoteOffmessages）.
NoteOn
Indicatesthataparticularnoteshouldbeplayed.Essentially,thismeansthatthenotestartssounding,butsomepatchesmighthavealongVCAattacktimethatneedstoslowlyfadethesoundin.Inanycase,thismessageindicatesthataparticularnoteshouldstartplaying（unlessthevelocityis0,inwhichcase,youreallyhaveaNoteOff）.IfthedeviceisaMultiTimbralunit,theneachoneofitsPartsmaysoundNoteOnsonitsownchannel.ThePartthatsoundsaparticularNoteOnmessageistheoneassignedtothemessage'
sMIDIchannel.
0x90to0x9FwherethelownibbleistheMIDIchannel.
Thefirstdataisthenotenumber.Thereare128possiblenotesonaMIDIdevice,numbered0to127（whereMiddleCisnotenumber60）.Thisindicateswhichnoteshouldbeplayed.
Theseconddatabyteisthevelocity,avaluefrom0to127.Thisindicateswithhowmuchforcethenoteshouldbeplayed（where127isthemostforce）.It'
suptoaMIDIdevicehowitusesvelocityinformation.OftenvelocityisbeusedtotailortheVCAattacktimeand/orattacklevel（andthereforetheoverallvolumeofthenote）.MIDIdevicesthatcangenerateNoteOnmessages,butdon'
timplementvelocityfeatures,willtransmitNoteOnmessageswithapresetvelocityof64.
ANoteOnmessagethathasavelocityof0isconsideredtoactuallybeaNoteOffmessage,andtherespectivenoteisthereforereleased.SeetheNoteOffentryforadescriptionofsuch.This"
trick"
wascreatedinordertotakeadvantageofrunningstatus.
AdevicethatrecognizesMIDINoteOnmessagesmustbeabletorecognizebotharealNoteOffaswellasaNoteOnwith0velocity（asaNoteOff）.TherearemanydevicesthatgeneraterealNoteOffs,andmanyotherdevicesthatuseNoteOnwith0velocityasasubstitute.
Intheory,everyNoteOnshouldeventuallybefollowedbyarespectiveNoteOffmessage（ie,whenit'
stimetostopthenote
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