Introduction to MIDI

Introduction

Introduction
M.I.D.I. stands for, "*Musical Instrument Digital Interface*," the new technology which gives musicians the ability to play more than one instrument at a time, sequence multiple performances for precise editing, score music as it is played, and much more!	The concept of MIDI is most easily understood as being a musical instrument communications network which enables MIDI equipped intruments to "talk" with each other through a common electronic language, MIDI Code 1.0.
MIDI was first introduced in 1983 when, in a display of mutual cooperation seldom seen in modern industry, several major musical equipment manufacturers demonstrated how competing producs could "play" together using MIDI code (which they had developed jointly). To the enormous benefit of all musicians, man manufacturers further agreed to use the MIDI specifications for all their future products.

What MIDI Is (and isn't) MIDI Channels

The first barrier for the novice to overcome is the misconception that MIDI transmits sound. Unlike records or tapes, which are a reproduction of the sound itself, MIDI devices "talk" to each other using a code that describes every aspect of their specific "performance" (such as which keys were struck, how hard they were hit, how long they were held, and so forth)" This performance data is transmitted as it is played (in real time) using MIDI code, but it is the instrument receiving the code which produces the sound. A good way to think of MIDI is to compare it to a roll of music in a player piano. The "performance" is on the roll, but the "sound" is in the piano. The single most powerful aspect of MIDI is it's ability to receive or transmit on one, all, or any combination of 16 channels simultaneously. Each channel is capable of either transmission ore reception of all MIDI messages independently of and simultaneously with all other channels. All MIDI devices receive, and most transmit MIDI messages (note numbers, preset change, etc.) instantaneously. (See Real Time)

What MIDI Is (and isn't)	MIDI Channels
The first barrier for the novice to overcome is the misconception that MIDI transmits sound. Unlike records or tapes, which are a reproduction of the sound itself, MIDI devices "talk" to each other using a code that describes every aspect of their specific "performance" (such as which keys were struck, how hard they were hit, how long they were held, and so forth)" This performance data is transmitted as it is played (in real time) using MIDI code, but it is the instrument receiving the code which produces the sound. A good way to think of MIDI is to compare it to a roll of music in a player piano. The "performance" is on the roll, but the "sound" is in the piano.	The single most powerful aspect of MIDI is it's ability to receive or transmit on one, all, or any combination of 16 channels simultaneously. Each channel is capable of either transmission ore reception of all MIDI messages independently of and simultaneously with all other channels. All MIDI devices receive, and most transmit MIDI messages (note numbers, preset change, etc.) instantaneously. (See Real Time)

MIDI Connections MIDI Patchbays & Thru Boxes

MIDI In: Receives the MIDI signal from a remote MIDI device such as a synthesizer or drum machine.
MIDI Out: Transmits the MIDI signal to the MIDI IN connection of another MIDI instrument or device.
MIDI Thru: Corresponds to MIDI IN, forwarding the MIDI signal to other instruments. This connection is a virtual hardwire connection, an exact duplication of the MIDI IN signal. Using MIDI THRU to connect many instruments can cause the signal to become degraded. For fewer than four instruments this is usually negligible, but it can be remedied entirely by the use of MIDI patchbays, splitters, or thruboxes.
MIDI Out MIDI In
Shown here is the typical MIDI jac configuration which is found on most instruments. Some MIDI devices don't have MIDI Thru, or use a switchable MIDI Out/Thru port.
These devices distribute the MIDI data stream into multiple data paths and allow you to connect many MIDI instruments to a single routing device. Some of the more sophisticated devices have programmable switching and merging between inputs and outputs as well as internal patch memories which can be accessed by the MIDI program change command.
MIDI Thru Box (or MIDI Splitter): A simple type of MIDI distribution network (but more than just a passive network) that consists of one or more MIDI inputs split into two ore more MIDI outputs. Common input-output configurations are 1x4, 1x6, and 2x8.
MIDI Patch Bay: A multiple in-and-out MIDI distribution box similar to, but more complex than a MIDI Thru Box. Patchbays provide many input/output combinations (6x8, 8x8, 15x16, 16x20 are common) and are becoming more sophisticated in order to support the many huge MIDI networks now evolving in studios and for live performances. Some patchbays offer features like LED data displays, MIDI merging, data filtering, patch offset adjustment, and internal memories with multiple presets.

MIDI Cables & Connectors

MIDI 1.0 specifications call for the use of 5 pin male DIN connectors soldered, at pins 4 and 5, to a twisted-pair wire wrapped with a fine wire mesh shield which is grounded to pin 2 to minimize radio frequency interference (RFI). (Pins 1 and 3 are not used at this time.) The MIDI standard specifies that cables run no longer than 50 feet without a booster. MIDI Connector WARNING!
Non-MIDI DIN connectors are used extensively for audio and computer equipment. Never connect a non-MIDI cable to MIDI equipment because RFI or other problems may occur. If you are making your own cables, be sure to use the exact MIDI specifications.

MIDI Connections	MIDI Patchbays & Thru Boxes
MIDI In: Receives the MIDI signal from a remote MIDI device such as a synthesizer or drum machine. MIDI Out: Transmits the MIDI signal to the MIDI IN connection of another MIDI instrument or device. MIDI Thru: Corresponds to MIDI IN, forwarding the MIDI signal to other instruments. This connection is a virtual hardwire connection, an exact duplication of the MIDI IN signal. Using MIDI THRU to connect many instruments can cause the signal to become degraded. For fewer than four instruments this is usually negligible, but it can be remedied entirely by the use of MIDI patchbays, splitters, or thruboxes. Shown here is the typical MIDI jac configuration which is found on most instruments. Some MIDI devices don't have MIDI Thru, or use a switchable MIDI Out/Thru port.	These devices distribute the MIDI data stream into multiple data paths and allow you to connect many MIDI instruments to a single routing device. Some of the more sophisticated devices have programmable switching and merging between inputs and outputs as well as internal patch memories which can be accessed by the MIDI program change command. MIDI Thru Box (or MIDI Splitter): A simple type of MIDI distribution network (but more than just a passive network) that consists of one or more MIDI inputs split into two ore more MIDI outputs. Common input-output configurations are 1x4, 1x6, and 2x8. MIDI Patch Bay: A multiple in-and-out MIDI distribution box similar to, but more complex than a MIDI Thru Box. Patchbays provide many input/output combinations (6x8, 8x8, 15x16, 16x20 are common) and are becoming more sophisticated in order to support the many huge MIDI networks now evolving in studios and for live performances. Some patchbays offer features like LED data displays, MIDI merging, data filtering, patch offset adjustment, and internal memories with multiple presets.
MIDI Cables & Connectors
MIDI 1.0 specifications call for the use of 5 pin male DIN connectors soldered, at pins 4 and 5, to a twisted-pair wire wrapped with a fine wire mesh shield which is grounded to pin 2 to minimize radio frequency interference (RFI). (Pins 1 and 3 are not used at this time.) The MIDI standard specifies that cables run no longer than 50 feet without a booster.		WARNING! Non-MIDI DIN connectors are used extensively for audio and computer equipment. Never connect a non-MIDI cable to MIDI equipment because RFI or other problems may occur. If you are making your own cables, be sure to use the exact MIDI specifications.

TROUBLESHOOTING

PATCH/PROGRAM OFFSET:A condition that occurs when MIDI devices utilize different types of numerical systems to identify their internal presets. For example, some intruments store presets in "banks" of eight. Bank one, preset one, would be displayed as '11' although the appropiate MIDI program change command would be '01.' Most manufacturers start numbering patches or presets from '00,' others begin at '01.' This means only that the user must recognize this situation and send the appropriate patch command.
STUCK NOTES (MIDI Choke): Notes can get "stuck" and continue to play if the instrument has received inappropriate commands, or if there is too much data for the instrument to thruput, or when the MIDI signal is interrupted because it hasn't received the correct note -off command (a common problem with older MIDI devices). Stuck notes can be turned off by either retriggering the instrument's voices, or by sending the all-notes-off command (#123) in real-time or on the instrument's sequencer track. (See MIDI Choke)
MIDI DELAY: (1.) A situation where MIDI devices are preceived to "logjam" (slow down). It is ususally caused bye the transmission of too much data through a single device, or just by the actual MIDI response times of different brands of equipment (a good thing to know). (2.) A second type of delay was caused by some early models routing data through the synthesizer's processing chip before returning it to the MIDI Thru. Present MIDI Thru's are hard-wired to the MIDI In and cause negligible degradation.
DEFAULT TO OMNI: This is the default channel mode setting specified in MIDI. OMNI responds to all notes on a ll channels and can cause confusion when an instrument plays all sixteen channels at the same time (i.e., keyboards play drum parts and vice versa). To alleviate this condition, make sure the receiving devices are in POLY mode with each one assigned to a seperate channel.
SENDING / RECEIVING VELOCITIES: Another situation which depends on the age and MIDI implementation of the particular instrument. There are many instruments that will receive but cannot transmit velocity information. Also, some instruments interpret velocity on a different response curve.
SENDING / RECEIVING AFTERTOUCH: Aftertouch is a fairly recent addition to most synthesizers and many older models will not respond to this command. Aftertouch uses averaged continual pressure messages after the initial strike of the note or chord to generate assignable controller data (0-127). This data can then be assigned to a controller number and used for any continuous controller function such as generating filter sweeps, pitch-bends, modultaion, etc.
ASSIGNING CONTROLLERS: Check the owner's manual for which controller numbers your instrument will send and/or receive. Make sure that both your transmitting and receiving devices are assigned to the controller number you wish to use. (See MIDI Controllers)

TROUBLESHOOTING
PATCH/PROGRAM OFFSET:A condition that occurs when MIDI devices utilize different types of numerical systems to identify their internal presets. For example, some intruments store presets in "banks" of eight. Bank one, preset one, would be displayed as '11' although the appropiate MIDI program change command would be '01.' Most manufacturers start numbering patches or presets from '00,' others begin at '01.' This means only that the user must recognize this situation and send the appropriate patch command. STUCK NOTES (MIDI Choke): Notes can get "stuck" and continue to play if the instrument has received inappropriate commands, or if there is too much data for the instrument to thruput, or when the MIDI signal is interrupted because it hasn't received the correct note -off command (a common problem with older MIDI devices). Stuck notes can be turned off by either retriggering the instrument's voices, or by sending the all-notes-off command (#123) in real-time or on the instrument's sequencer track. (See MIDI Choke) MIDI DELAY: (1.) A situation where MIDI devices are preceived to "logjam" (slow down). It is ususally caused bye the transmission of too much data through a single device, or just by the actual MIDI response times of different brands of equipment (a good thing to know). (2.) A second type of delay was caused by some early models routing data through the synthesizer's processing chip before returning it to the MIDI Thru. Present MIDI Thru's are hard-wired to the MIDI In and cause negligible degradation.	DEFAULT TO OMNI: This is the default channel mode setting specified in MIDI. OMNI responds to all notes on a ll channels and can cause confusion when an instrument plays all sixteen channels at the same time (i.e., keyboards play drum parts and vice versa). To alleviate this condition, make sure the receiving devices are in POLY mode with each one assigned to a seperate channel. SENDING / RECEIVING VELOCITIES: Another situation which depends on the age and MIDI implementation of the particular instrument. There are many instruments that will receive but cannot transmit velocity information. Also, some instruments interpret velocity on a different response curve. SENDING / RECEIVING AFTERTOUCH: Aftertouch is a fairly recent addition to most synthesizers and many older models will not respond to this command. Aftertouch uses averaged continual pressure messages after the initial strike of the note or chord to generate assignable controller data (0-127). This data can then be assigned to a controller number and used for any continuous controller function such as generating filter sweeps, pitch-bends, modultaion, etc. ASSIGNING CONTROLLERS: Check the owner's manual for which controller numbers your instrument will send and/or receive. Make sure that both your transmitting and receiving devices are assigned to the controller number you wish to use. (See MIDI Controllers)

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