Transcript Lecture Slides

Field Trip #20
Creating Simple Music
By Keith Lynn
Midi
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Midi stands for Musical Instrument Digital
Interface
It is an interface that allows a variety of
instruments to connect and communicate with
each other
A single midi link can carry up to 16 channels of
information
We can connect a channel to a different device
Midi cont'd
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A Midi Event message carries information about
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Pitch
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Notation
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Velocity
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Volume
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etc
Instrument
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An instrument is represented by an integer
between 0 and 255
You can find a list of instruments at
http://www.ccarh.org/courses/253/handout/gmii
nstruments
Creating the Midi
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In order to create the midi, we will create a
Sequencer
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After we create the Sequencer, we open it
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We create a Sequence
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The Sequence is made of Tracks
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The Tracks are made up of MidiEvents
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The MidiEvent is composted of a MidiMessage
and a tick. The tick indicates the time in the
sequence where the event fires
MidiMessage
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In this app, we will create a simple message
A ShortMessage contains two bytes of
information
To create the ShortMessage, we specify four
things
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A Midi command
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A channel
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The first data byte
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The second data byte
Midi Commands
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The ShortMessage class contains constants
that represent Midi commands
Some of the most common are
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Note on – Start Playing
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Note off – Stop Playing
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Program change – Specify what instrument is on a
channel
Playing Notes
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The third parameter to create the
ShortMessage is a note
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Middle C is 60
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The fourth parameter is the velocity
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Typically we can use 100
Playing the sound
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In order to play the Midi sound, we create the
ShortMessages and create a MidiEvent
The MidiEvent specifies the ShortMessage and
the tick
The tick is the time when the event fires
Creating the Midi Player
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In our app, we allow the user to specify through
Java components, the values to create a
ShortMessage
These ShortMessages appear in a Jpanel
When we are ready to play, we click Play and
each of the MidiMessages are put into a track,
and the track put in a sequence, and the
sequence put in the sequencer
Storing MidiEvents
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In our app, we create a Jpanel called a
MidiMessagePanel
This class is declared to be Serialiazable
This means that instances of the class can be
written to a file
Later we can read them back in
In order to write the objects, we use an
ObjectOutputStream, and in order to read the
objects, we use an ObjectInputStream