MIDI
MIDI (short for Musical Instrument Digital Interface) is a technical standard that describes a protocol, digital interface and connectors and allows a wide variety of electronic musical instruments, computers and other related devices to connect and communicate with one another.{1} A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device. MIDI carries event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, audio panning, cues, and clock signals that set and synchronize tempo between multiple devices. These messages are sent to other devices where they control sound generation and other features. This data can also be recorded into a hardware or software device called a sequencer, which can be used to edit the data and to play it back at a later time.{2} |
MIDI events can be sequenced with computer software, or in specialized hardware music workstations. Sequencers allow composers to audition and edit their work much more quickly and efficiently than did older solutions, such as multitrack recording. They improve the efficiency of composers who lack strong pianistic abilities, and allow untrained individuals the opportunity to create polished arrangements. Because MIDI is a set of commands that create sound, MIDI sequences can be manipulated in ways that prerecorded audio cannot. It is possible to change the key, instrumentation or tempo of a MIDI arrangement, and to reorder its individual sections. The ability to compose ideas and quickly hear them played back enables composers to experiment. Algorithmic composition programs provide computer-generated performances that can be used as song ideas or accompaniment. Some composers may take advantage of MIDI 1.0 and General MIDI (GM) technology to allow musical data files to be shared among various electronic instruments by using a standard, portable set of commands and parameters. On the other hand, composers of complex, detailed works to be distributed as produced audio typically use MIDI to control the performance of high-quality digital audio samples and/or external hardware or software synthesizers.
Many digital audio workstations (DAWs) are specifically designed to work with MIDI as an integral component. MIDI piano rolls have been developed in many DAWs so that the recorded MIDI messages can be extensively modified. Virtual Instruments created by third party companies in one of a number of commonly used formats (for example, VST or RTAS) may be loaded as plug-ins thus providing a virtually limitless supply of sounds for a musician, and are designed to be commanded by MIDI controllers, especially in the DAW environment. The data composed via the sequenced MIDI recordings can then be saved as a Standard MIDI File (SMF), digitally distributed, and reproduced by any computer or electronic instrument that also adheres to the same MIDI, GM, and SMF standards.
MIDI data files are much smaller than recorded audio waveforms. Many computer-sequencing programs allow manipulation of the musical data such that composing for an entire orchestra of sounds is possible. This ability to manipulate musical data has also introduced the concept of surrogate orchestras, providing a combination of half sequenced MIDI recordings and half musicians to make up an entire orchestral arrangement; however, scholars believe surrogate orchestras have the possibility of affecting future live musical performances in which the use of live musicians in orchestral arrangements may cease entirely because the composition of music via MIDI recordings proves to be more efficient and less expensive.
General MIDI
MIDI allows selection of an instrument's sounds through program change messages, but there is no guarantee that any two instruments have the same sound at a given program location. Program #0 may be a piano on one instrument, or a flute on another. The General MIDI (GM) standard was established in 1991, and provides a standardized sound bank that allows a Standard MIDI File created on one device to sound similar when played back on another. GM specifies a bank of 128 sounds arranged into 16 families of eight related instruments, and assigns a specific program number to each instrument. Percussion instruments are placed on channel 10, and a specific MIDI note value is mapped to each percussion sound. GM-compliant devices must offer 24-note polyphony. Any given program change will select the same instrument sound on any GM-compatible instrument. The GM standard eliminates variation in note mapping. Some manufacturers had disagreed over what note number should represent middle C, but GM specifies that note number 69 plays A440, which in turn fixes middle C as note number 60. GM-compatible devices are required to respond to velocity, aftertouch, and pitch bend, to be set to specified default values at startup, and to support certain controller numbers such as for sustain pedal, and Registered Parameter Numbers. A simplified version of GM, called "GM Lite", is used in mobile phones and other devices with limited processing power. |
http://en.wikipedia.org/wiki/Midi
{1} Swift, Andrew. (May-Jun 1997.), "A brief Introduction to MIDI",SURPRISE (Imperial College of Science Technology and Medicine), retrieved 22 August 2012
{2} Huber, David Miles. "The MIDI Manual". Carmel, Indiana: SAMS, 1991.
{1} Swift, Andrew. (May-Jun 1997.), "A brief Introduction to MIDI",SURPRISE (Imperial College of Science Technology and Medicine), retrieved 22 August 2012
{2} Huber, David Miles. "The MIDI Manual". Carmel, Indiana: SAMS, 1991.