Musical Instrument Digital Interface, - Hol.gr

MIDI in Multimedia Applications
MIDI takes up less space than digital audio files which makes it a valuable option in many Multimedia
programs. Some programs use a combination of MIDI and digital audio files. MIDI may be used in the
HyperCard and SuperCard programs. It may be imported into the audio tracks of a QuickTime Movie and
sophisticated Multimedia program like Director may use MIDI files as well as sound files. The new
internet browsers have plug-in capabilities that allow MIDI files to played over a web site (see Using
MIDI on a Web Site).
Sometimes, this subject is a little confusing because both formats are referred to as digital information.
This page will try to explain the content of both signals and clear up some misconceptions about the two
formats.
• Digital Signal
Files
• Computation of Digital
Signals
Digital Signals
• MIDI Files
First let us start by describing an analog signal. The word analog implies a resemblance or similar
comparison of one thing representing another. An analog signal is a transformation of an acoustic signal,
movement of molecules in a medium such as air, to a voltage signal that travels down an electrical wire.
The voltage in the wire is an analog or representation of the acoustic signal. A typical set-up may be a
musical instrument that creates a tone. This tone energy creates a disturbance in the air particles by
pushing air molecules that condense and cause a rarefaction of the air when it returns. This movement is
happening at a fast rate that equals the initial source of the soundwave. This tone is then received by a
microphone that has a sensitive diaphragm that responds to the movement of air. At this point we use a
term called transducer, because the energy is converted from an acoustic signal to an electrical signal than
represents the same waveform. This voltage signal is then carried down a wire to an amplifier, where the
signal is amplified and then sent down another wire to a loudspeaker, which transforms the signal back to
acoustic energy that is received by the auditory system.
Another example of analog signals are the use of the older modular type synthesizers that use voltage to
carry the musical signal down a wire. Alterations to the signal, such as filters, ring modulators, simple
frequency modulation, sample and hold are modifiers that are used to alter the analog signal.
In the digital world, numbers are used to represent a digital waveform. An audio signal is represented in
digital memory with a binary code that stores a massive amount of numbers that are used to represent a
signal. An ADC (Analog to Digital Converter) is a computer chip that is used to convert an analog signal