The MIDI interface
The digital data transmitted
|Basic MIDI set-up |
MIDI for Performance
MIDI for Composition
MIDI is the acronym for Musical Instrument Digital Interface. It was defined by the Midi 1.0 specification which was agreed upon in august 1982. It was based upon the idea of a Local Area Network, since it was relatively inexpensive and simple to set up and run. It superseded the non-standard method called "gate/Control Voltage". The main problems with gate/CV is that it lacks sophistication. Analogue keyboards used with this system have complex sound generation techniques.(Attack, decay, sustain, release) It is not possible to send this kind of information when using the gate/CV technique, resulting in "lifeless" sounds.
The development of MIDI has had a considerable impact on the development of electronic music. Modern dance music,Techno, House, Drum and Bass etc, could not have developed in their current state without this technology. The complexity of older systems meant that only a few people had access. With MIDI it is possible to set-up a "home studio" quickly and relatively cheaply. This encourages the development of experimental music, which is how modern dance music started.
There are many reasons why MIDI is used by such a large number of people. The most significant being that it is the system that all keyboard manufacturers have used in the design of their digital synthesizers. MIDI has many uses and appeals to a wide range of people, from futuristic music Composers to solo artists. There are now even MIDI products on the market that allow the controlling of light rigs. Considering the capabilities of the system the cost of setting up a MIDI system is relatively low. The price of a budget system is about eighty to a hundred pounds (keyboard £50 pounds MIDI interface with software 30 pounds RE:John's MIDI Center, 160 Deansgate, Manchester)
The MIDI interface
The MIDI interface has three ports. MIDI: IN, OUT and THRU. The IN port allows data to be received by the machine. The OUT port is used for transmitting data. The THRU port creates a replica of the input signal. This is used to connect more than one MIDI device. At first glance it may seem unnecessary to have the THRU port, since you could simply chain devices together using the output from the OUT port. The digital information is sent serially at a rate of 3000 bytes per second, by switching a current of approximately 5mA on and off. If the OUT port was used this current may be too small to drive any of the devices.
The Digital Data Transmitted
Every MIDI message transmitted starts with a "Start Bit", this is when the signal current drops to 0mA, and is followed by a byte of data (Most Significant Bit (MSB) is transmitted first) and finishes with a "Stop Bit", which is when the current returns to 5mA.The RS232 system works in a similar way.
Basic MIDI set-up
Using MIDI for performance
MIDI as a backing track
The sequencer is pre-programmed with MIDI information for the song. There are several tracks, one for the bass drum, cymbal, bass line etc, each of which are assigned a channel. The sequencer then sends the data serially at a rate of 3000 bytes per second. The sampler is programmed so that it uses data from only the channels which it has been assigned to. If for example channel 1 has the information for the bass line and channel 2 is used for the bass drum the sampler should only respond when it receives channel 1 data and ignore channel 2 data. The complete input to the sampler is passed on almost instantaneously using the THRU port to the drum machine, which will pick out only the channels meant for drum sounds.
This set up is fine for small systems. With larger systems, the chaining of data using the THRU port causes small but significant delays.
An example of a large MIDI system
In this example system instead of chaining together MIDI devices I have used a MIDI THRU Box, which takes the input from the sequencer and sends the data in parallel to each of the devices, this removes delays associated with chaining.
The Wind controller is a device that allows a wind instrument muscian the use of MIDI. The wind controller and guitar send data in the same way as a MIDI keyboard. They are just played in a different manner.
This was a radio show about the band Kraftwerk, and the influence of the band on the modern day dance music. The Band were pioneers of experimental electronic music.