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MIDI - Multimedia - Lecture Slides, Slides of Multimedia Applications

English and Foreign Languages UniversityMultimedia Applications

The main points are:Midi, Adding, Applications, Memory Intensive, Large Soundfiles, Minute, Ringtones, Cellphone, Considered, AlternativeMidi, Adding, Applications, Memory Intensive, Large Soundfiles, Minute, Ringtones, Cellphone, Considered, Alternative

Typology: Slides

2012/2013

Uploaded on 04/29/2013

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MIDI
•One choice for adding sounds to multimedia
applications is the use of digital audio soundfiles
–This can become very memory intensive, however, for
large soundfiles
–For example, a stereo 16 bit/sample 22 kHz soundfile
requires > 5 mbytes per minute of audio
–May be too much (e.g. for ringtones on a cellphone)
•As an alternative to the use of soundfiles, MIDI
files have been considered
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Download MIDI - Multimedia - Lecture Slides and more Slides Multimedia Applications in PDF only on Docsity!

MIDI

  • One choice for adding sounds to multimedia applications is the use of digital audio soundfiles - This can become very memory intensive, however, for large soundfiles - For example, a stereo 16 bit/sample 22 kHz soundfile requires > 5 mbytes per minute of audio - May be too much (e.g. for ringtones on a cellphone)
  • As an alternative to the use of soundfiles, MIDI files have been considered

MIDI

  • MIDI (Musical Instrument Digital Interface) is a standardized control language and hardware specification - allows suitably equipped electronic musical instruments and devices to communicate real-time and nonreal-time performance and control data
  • MIDI data is communicated digitally through a production system as a string of MIDI messages
  • Each message describes an event which occurs during a musical performance

MIDI

  • MIDI messages are transmitted (in a serial

fashion) through a single MIDI line at 31.25 K

bits/second

  • MIDI communication is unidirectional
  • No error detection/correction (so max cable length of 50 meters)
  • Usually, MIDI instruments and devices are

linked together in a daisy-chain fashion

  • The following slide shows an example

MIDI Devices

  • MIDI controllers generate performance data in MIDI format
  • MIDI synthesizers generate audio output based on MIDI data - A single keyboard might act as both MIDI controller and MIDI synthesizer - A synthesizer can be some hardware (instrument) or a program (soft synth)
  • MIDI sequencers can be used to receive, store and edit MIDI data - Either hardware device or an application program

MIDI Sequencers

  • The sequencer software will typically run on a Digital Audio Workstation (DAW) - Originally, special purpose microprocessor-based hardware for capturing, editing, creating music - Today, a computer running special-purpose software with audio hardware interfaces - Example sequencing software – Cubase
  • Examples of hardware-based sequencers are MIDI keyboards and drum machines - These also may contain a synthesizer component

Musical Acoustics and Notation

  • Musical sounds are characterized by pitch (frequency), timbre , loudness
  • A note also carries start and duration info
    • Two notes which differ in pitch by 2^n, sound alike to the human ear (except for the higher pitch)
    • An octave is the interval between one musical pitch and another with half or double its frequency
    • The division into notes of an octave differs from culture to culture
    • In Western culture, 440 Hz is a reference point and is called note A
    • The octave between one note A and another (440-880 Hz, e.g.) is divided into 12 notes

Musical Acoustics and Notation

  • On a keyboard, 8 white notes and 4 black notes
  • Musical notation is written on a musical staff , with a key signature
  • The timbre of a musical sound is a function of its overtones
  • The perceived loudness of a musical sound is a function of the air pressure amplitude - The amplitude envelope covers the period of a single musical note

Musical Acoustics and Notation

  • MIDI messages are bytes that are interpreted

by the MIDI devices

  • The messages are used to convey a series of instructions to one or all of the MIDI devices within the system.
  • The messages can be divided into two types:
  • Channel messages are messages assigned to a specific MIDI channel
  • System messages address all devices in a system, without regard to channel assignment
  • Messages are transmitted in 10 - bit bytes

MIDI Messages

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MIDI Channels

MIDI Channel Messages

  • Whenever a MIDI device is instructed to respond to a specific channel number, it will ignore any message not directed to that channel - On the other hand, if a message is transmitted to that channel, the device will respond to the message (within the device’s capability limits).
  • The 7 bits (not including the MSB) of the first data byte code the note # that should be turned on - here, it is 64
  • The 7 bits of the second data byte indicate the attack velocity (volume level of the note) - here, it is 90

MIDI Channel Voice Messages

  • A Note On message indicates the beginnning of a MIDI note
  • The message consists of three bytes of information: MIDI channel number; MIDI note number; Attack velocity value - In general, MIDI note 60 is assigned to middle C key, and notes 21- correspond to the 88 keys of an extended keyboard controller
  • The final byte indicates the velocity at which the key was pressed - Higher velocities lead to louder notes - Not all instruments interpret all attack velocities, and some do not respond dynamically at all

MIDI Channel Voice Messages

  • A Note Off message indicates the end of a

MIDI note

  • If the instrument being played has a release (or decay) phase, it will begin that phase when the message is received
  • The release velocity byte indicates the speed at which the key was released - Few instruments generate or respond to release velocity