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Intro to Music Technology MIDI Basics

Part V

Intro MIDI is everywhere around us. It's in musical instruments, computers,

cell phones, and many other products from well known companies like Microsoft, Apple, Nokia, Sony, Yamaha, & hundreds more consumer products companies.

Most popular recorded music is written and performed using MIDI-equipped electronic keyboards (aka "synthesizers"). Much music is also written on computers using "Sequencers" and/or "Digital Audio workstations". Other MIDI-equipped musical instruments may also be used, including digital drums, digital guitars, wind instruments, and more.

Your computer probably has the ability to play MIDI files using either built-in hardware or a software synthesizer that responds to MIDI messages, and with an appropriate adapter your computer can be connected to other MIDI-equipped products so you can use MIDI to help you learn, play, create and enjoy music.

Even film and TV scores are usually created on MIDI instruments, and with advances in digital sampling and synthesis technologies making digital instruments sound ever more realistic, the orchestra playing behind that big-screen block buster is more likely to be the product of a few MIDI devices than dozens of acoustic instruments.

Besides music creation and playback described above, MIDI has some other interesting and popular uses. MIDI Show Control is a different set of MIDI messages used for controlling rides at theme parks as well as for operating themed events such as are found outside many Las Vegas casinos. And many people have developed unique products that use MIDI.

And if you own a cell phone that has "polyphonic ring-tones" (billions do) it's probably got a MIDI synthesizer built-in (or something very much like MIDI, depending on the manufacturer). Ring-tones are a very popular add-on business for cellular providers, and many people use MIDI to make their own ring-tones and put them on their phones.

The Basics

MIDI, pronounced “Mid-ee” is an acronym for Musical Instrument Digital Interface. At it’s most basic, it is a standardized communications protocol that allows musical instruments and computers to talk to each other using a common language.

MIDI is a standard, a protocol, a language, and a list of specifications. It identifies not only how information is transmitted but also what hardware transmits this information. It specifies how cables are connected and what type of

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cables should be used to transmit MIDI data. MIDI has as many software implementations as it has hardware ones.

At it’s most basic level, MIDI was conceived as a way to link 2 or more synthesizers together to “layer” sounds. It now is used to control studio equipment, light shows, and even control factory automation.

Brief History of MIDI

Throughout the history of electronic music, musicians have wanted to connect

multiple instruments together to create a whole greater than the sum of its parts. The greatest stumbling block was that instruments from one company were incompatible with instruments from another.

Moog is generally, and appropriately, credited for taking the synthesizer

out of the university laboratory and putting it in the hands of musicians.

Certainly from the time of Walter Carlos' ground-breaking Switched On Bach recording (1968) to the release of the MiniMoog (1970) both musicians and the music-buying public became enamored – if not frankly dazzled – by the sonic possibilities now seemingly on the musical horizon.

As it turned out it was a false dawn. The synthesizers of the 1970s might have been unrestricted sonically but in terms of playability, stability, polyphony, and compatibility they were still very limited indeed.

Early integrated circuits-based synthesizers from Moog, ARP, and EMS opened the door but it was the arrival of Japanese companies like Korg, Roland, and Yamaha in the mid 1970s that converted potential into popularity.

Digitally Controlled Synthesizers

The popularity of synthesizers got a major boost in 1978 when micoprocessor-based instruments began to appear, spearheaded by a new California company called Sequential Circuits.

The Prophet-5, though still hugely limited by today's standards, offered reasonable levels of playability, stability, and polyphony, albeit at a hefty price at

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the time (around $4000). Soon Korg, Roland, and Yamaha's microprocessor-based offerings would slash prices in half, and by the turn of the decade the polyphonic synthesizer was firmly on the map for every self-respecting keyboard player from hobbyists to touring professionals. “The days of the Hammond organ, the Fender Rhodes piano, and the Hohner Clavinet were coming to an end”… or so we thought…

Stability, playability, and polyphony continued to evolve in the early 1980s but compatibility remained a thorn in the side of manufacturers.

MIDI concept is born

Visionaries like Dave Smith from Sequential Circuits, and Ikutaru Kakehashi from Roland began to worry that this lack of compatibility between manufacturers would restrict people's use of synthesizers, which would ultimately inhibit sales growth. Talk of a ‘universal' digital communication system thus began circulating in 1981. Dave Smith and Chet Wood presented a paper that year at AES (Audio Engineering Society) proposing a concept for a Universal Synthesizer Interface.

At this time there were 7 major players in the synthesizer manufacturing

business; Arp, Moog, Oberheim, Sequential Circuits, (US) and Roland, Korg and Yamaha, (Japan). There were others as well but these were the big players capturing most of the market share. They were all talking about how great and profitable it would be to get instruments to be able to connect to each other.

At the following NAMM (National Association of Music Merchandisers)

show in January 1982 a meeting took place between the leading American and Japanese synthesizer manufacturers where certain improvements were made to the USI specification and the acronym MIDI was adopted.

The following year, the first public presentation of a working MIDI

connection took place in 1983 at the winter NAMM show. A Sequential Circuits Prophet-600 was connected to a Roland Jupiter 6 by each synth's MIDI interface. Connecting synthesizers together certainly was not a new idea, but this means of doing so was new and far more effective than earlier solutions.

• In the summer of the same year, Yamaha introduced the DX7 FM

synthesizer, with MIDI hardware as a standard component. MIDI rapidly found favor with manufacturers that recognized the advantages of

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standardizing a basic hardware/software interface for data exchange among different machines. It is no exaggeration to say that MIDI fueled an incredibly active period of hardware synthesis development during the late 1980s and early 1990s.

MIDI and the Personal Computer

Simultaneously, the personal computer (PC) was emerging as a potential tool for musicians because of its programmability. Roland seized that opportunity and began work on a musical interface device for the IBM PC. Roland saw the PC as being a digital alternative to its analog sequencers, and since this hardware device would allow musical instruments to communicate with IBM PC computers, it was the perfect interface tool to penetrate new markets.

Roland MPU-401 1984

(Musical Processing Unit) By 1985, the Commodore 64, Apple II, and IBM PC could all be adapted for MIDI. The Atari 512 even had a MIDI interface built in. In 1986, Apple came out with the very popular Macintosh Plus, which quickly became a favorite with musicians because of its GUI.

Music Software

Now that computers could speak MIDI, many new software companies started creating programs for sequencing. Some of the first….

• Steinberg Research GmbH – 1984 - now known as Steinberg (owned by Yamaha) created and developed the first MIDI Multitrack Sequencer.

First product: Pro-16 for the Commodore 64 Current products: DAW products include Cubase and Nuendo.

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• MOTU – 1985 (Mark of the Unicorn) First product: Performer (Apple Macintosh only) Current product: Digital Performer 6 (Mac only)

• Twelve Tone Systems – 1987- now known as Cakewalk.

First product: Cakewalk version 1 for DOS Current product: DAW products include Sonar

• C-Lab – 1988 - later Emagic – now owned by Apple First product: Creator Current product: DAW Logic Pro 8

• Software houses created and marketed music composition programs and other MIDI software. Equipped with the right hardware and software, a musician could use the computer to control synthesizers, drum machines, mixers, effects units--anything equipped with MIDI connectors. The extent of control varied, but the efficiency of the MIDI studio made a revolutionary impact on music production.

• One of the advantages of MIDI’s modular concept is that you could now

pick and choose system components that best suit your needs. Your favorite keyboard could be linked to any MIDI instrument you please. To add additional synthesizers, you don’t necessarily need more keyboards. The newly developed concept of the synthesizer module would save space and money.

What is MIDI?

The Musical Instrument Digital Interface (MIDI) allow musicians, sound and lighting engineers, computer enthusiasts, or anybody else for that matter to use multimedia computers and electronic musical instruments to create, listen to, and learn about music by offering a common language that is shared between compatible devices and software.

MIDI can be divided into 3 categories.

1. The Protocol – the language MIDI uses. 2. The Hardware Interface – the connections and cables MIDI uses

to transmit and receive its information.

3. The File Formats – how MIDI manages and manipulates the data. Standard MIDI Files (SMF) – Music Editing - Sequencing

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1. Protocol

The Protocol of MIDI is a music description language in binary form, in which binary words describe an event of a musical performance.

• MIDI was originally intended for keyboard instruments, so many of its

events are keyboard oriented, where the action of pressing a note is like activating an On switch, and the release of that note is like turning a switch Off.

Status and Data Bytes There are two types of bytes, Status or Data.

• All Status bytes begin with a 1 as the MSB and are the first byte

transmitted when sending any MIDI command. They serve to identify the kind of information being sent over MIDI. It tells the receiving device which MIDI channel the event belongs to and what the event is. For example, an event can be a Note On, Note Off, Pitch bend, program change, etc…

All Data bytes begin with a 0 as the MSB and usually 1 or 2 data bytes

follow a status byte. They represent some value associated with the status byte. For example, when you strike a middle C on the transmitting keyboard with fairly heavy force, the Status message would hold a “note on” and the Data message would be a note value number of 60d and a velocity level of maybe about 114d.

Note On command Transmits 3 message bytes 1st byte – Status byte - Note On command and MIDI Channel 2nd byte – Data byte – MIDI note number (0-127) 3rd byte – Data byte – Velocity (0-127) 90h or 10010000 = Note On command on MIDI channel 1 3Ch or 00111100 = MIDI note number 60d or middle C 72h or 01110010 = Velocity value of 114d, fairly high value

Status messages use numbers ranging from 128d (80h, 10000000b) to 255d (FFh, 11111111). The Data messages use numbers ranging from 0d (00h, 00000000b) to 127d (7F, 0111111b). Again, the first bit (MSB)

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determines if it is a Status or Data message.

MIDI actually uses a 10-bit word when it transmits. 8-bits are for information (Status or Data) and the 2 extra bits are used for error correction.

Since the MSB is only used to designate whether the message is Status or

Data, this only leaves 7-bits of values for the rest of the word. The values of 7-bits range from 0-127d. This is why you will notice that values in MIDI are often numbered from 0 to 127. When you adjust the controls on some MIDI instruments you will see values range from 0 to 127.

• MIDI messages are often represented in one of three formats: decimal,

binary, and hexadecimal.

• An entire MIDI message can contain up to 3 bytes of information depending on the MIDI function. The status byte always begins with a 1 and is like the engine pulling the cars (data). The next 3-bits of the status byte identify the MIDI function and the last 4-bits identify the MIDI channels 1-16. (Except System Common messages, which are sent out to all MIDI channels).

16 MIDI Channels 1-16 (0000 – 1111)

A MIDI channel is like a television or radio channel. It is a way for MIDI to isolate information so that a receiving instrument set to a certain channel will filter out all the other information in the transmission, and reproduce or process only the information to which it is tuned. Most synths built today are multi-timbral instruments. They can play more that one sound at a time. Using MIDI channels we can access up to 16 sounds per synth. If your instrument is multi-timbral, it will retain only the MIDI messages that apply to its active channels. Let’s say you have a multi-timbral instrument set to play channels 1 through 5; this instrument will ignore all messages sent out MIDI channels 6 through16.

MIDI Message Types (Status bytes)

All aspects of your musical performance can be represented in a MIDI message. The following section will identify these aspects and explain how they work and what values are attached to them. To better understand these aspects of MIDI messages, the Status bytes have been divided into five categories.

Channel Voice Messages are the basic MIDI events representing a

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musical performance. The most common Channel Voice Messages are Note On and Note Off, Pitch Bend, Program Change and After Touch.

Channel Mode Messages tell devices to send or receive

information in a certain way, which is defined by the mode being sent. An example would be making a device respond in omni/off mode instead of omni/on mode. In omni/off mode the device would only receive information on its basic channel. In omni/on mode it can receive data on all 16 channels.

System Common Messages are, as the name would suggest,

common to all instruments, devices, or software in your MIDI setup. Sequencers use System Common Messages for MIDI time references (using MIDI Time Code), song position, song selection and tuning.

System Real Time Messages are synchronization commands used

by MIDI to control sequences, such as Start and Stop commands imbedded as a MIDI command, along with the MIDI Timing Clock.

System Exclusive Messages are used to send or receive

instrument settings such as patch or performance memories. You can also use System Exclusive (SysEx) messages to transfer sample waveforms via MIDI along with other non-music related functions.

Channel Voice Messages

This is the backbone of MIDI. Most of what MIDI sends in a live performance are Channel Voice messages. The following section will describe each of those message types so you can understand what is transmitted through MIDI and where to look when editing a MIDI sequence recorded in a MIDI sequencer. Note Off (80-8F 1000cccc) This message is sent when you release a note after striking it. (Now days, most devices will use a Note On message with a velocity value of 0 to indicate that the note is off.) If your keyboard supports Release Velocity sensing, which detects how fast you release the key, this can be used to change some aspect of the sound. Ex., like a slow release could change the release envelope of a patch making the sound slowly decay instead of a quick decay. Note On (90-9F 1001cccc) Every time you play a note, a Note On message is sent. This Note On message contains two pieces of information (besides the

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MIDI channel): the key or note number and the velocity at which the note was played. Both of these are data bytes and their values can be between 0 and 127. Below are charts for MIDI note numbers and velocity range.

MIDI NOTE Numbers Octave C C#/Db D D#/Eb E F F#/Gb G G#/Ab A A#/Bb B

-1 0 1 2 3 4 5 6 7 8 9 10 11 0 12 13 14 15 16 17 18 19 20 21 22 23 1 24 25 26 27 28 29 30 31 32 33 34 35 2 36 37 38 39 40 41 42 43 44 45 46 47 3 48 49 50 51 52 53 54 55 56 57 58 59 4 60 61 62 63 64 65 66 67 68 69 70 71 5 72 73 74 75 76 77 78 79 80 81 82 83 6 84 85 86 87 88 89 90 91 92 93 94 95 7 96 97 98 99 100 101 102 103 104 104 106 107 8 108 109 110 111 112 113 114 115 116 117 118 119 9 120 121 122 123 124 125 126 127 - - - -

Velocity range reference. Musical Expression Musical Notation MIDI velocity range Extremely soft ppp 1 - 15 Pianissimo (very soft) pp 16 - 31 Piano (soft) p 32 - 47 Mezzo Piano (moderately soft) mp 48 - 63 Mezzo Forte (moderately hard) mf 64 - 79 Forte (loud or hard) f 80 - 95 Fortissimo (very loud or hard) ff 96 - 111 Extremely loud or aggressive fff 112 - 127

Polyphonic Aftertouch (A0-AF 1010cccc) Aftertouch is a modulation source and be made to do whatever in the receiving instrument. Vibrato and filter sweeping are common uses of aftertouch. This function determines the amount of aftertouch pressure you put on each key that is being held down (note on). It sends out continuous bytes of data for each note as you press harder or softer on the keys. This can add up to a lot of MIDI data being transmitted. Program Change (C0-CF 1100cccc) Sending this message out will cause the receiving unit to change its program. Some manufacturers might call them presets, patches, instruments or whatever.

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Channel Aftertouch (D0-DF 1101cccc) Like Polyphonic aftertouch except it takes the value of the key that is being pressed the hardest and sends that data out. All keys that are being played will respond to the data that is being sent out by the key with the most pressure. The result is less data being transmitted and all keys that are being played will have the same amount of aftertouch modulation applied to them. Pitch Wheel (E0-EF 1110cccc) Pitch bending can make the sound more expressive, somewhat like a wind instrument. Because the human ear is very sensitive to pitch changes, the pitch bend message contains two data bytes to determine the bend value (214). This gives a resolution of 16,384 steps, which is usually split in 2, with +8,192 steps above and -8,192 steps below with 0 being the original pitch. This smoothes out the stair-stepping effect that would result with only 128 steps. Pitch bend control is a Continuous Controller type since it continuously sends MIDI messages to update the receiving MIDI device on the position of its controller. Control Change and Channel Mode (B0-BF 1011cccc) The Keys are not the only way to control the sound. There are 128 control changes that are defined in the 2nd Data byte. Devices such as a modulation wheel, sustain pedal, volume control, expression pedal, breath controller and many more are used to give you more control over the expressive elements of a sound. Some are Continuous Controller type and some are Switch Controller type. Included under this status byte are the Channel Mode messages.

Channel Mode Messages

The Local control on/off is under this status byte. It enables/disables the keyboard from transmitting MIDI data to its own internal sounds. When a keyboard is connected to a DAW’s sequencer, the MIDI data is received and transmitted back out to the sending device. This can double the MIDI data in the keyboard since it is receiving from both the DAW and its own keyboard. By turning off local control, the device only receives from the DAW.

Channel Mode: This Status byte also directs us to the Channel Mode functions. This determines how a device will respond to MIDI messages in and out. There are 4 modes of operation that are combined in four ways.

Omni on mode – implies that a device can respond to all or any incoming MIDI channel data, regardless of its channel. Omni off mode – implies that a device can only respond to its base MIDI channel. For instance, if you set your keyboard to channel 1, it will only receive data that is on channel 1, and transmit data on channel 1. Poly mode – implies that a device is capable of polyphony and will enable polyphonic playing of any MIDI channel.

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Mono mode – implies that a device will not play more than one note at a time on any given channel. Mode 1 – Omni On/Poly rarely used since data on any MIDI channel will be played back on the devices base channel. Mode 2 – Omni On/Mono rarely used – same as Mode 1 except it will only play back monophonically (1 note at a time). Mode 3 – Omni Off/Poly Most used in today’s MIDI world. The device will respond to MIDI channel data and play back with polyphony. Mode 4 – Omni Off/Mono rarely used – same as above but will playback in mono.

System Common, System Real Time and System Exclusive Messages

System Common (F0-FF 1111nnnn) System Common messages are intended for all MIDI channels in a system so the last 4bits define message types, not MIDI channels. The System Real Time and System Exclusive messages are included in this Status byte. Most system common messages relate to synchronization features and are used with sequencers since they relate to time positioning, song selection, and features on your MIDI device. Here’s a look at these messages from the last 4 bits. F0 11110000 System Exclusive message status byte F1 11110001 MIDI Time Code Qtr. Frame status byte F2 11110010 Song Position Pointer status byte

F3 11110011 Song Select (song#) F4 11110100 Undefined F5 11110101 Undefined F6 11110110 Tune Request F7 11110111 End of SysEx (EOX) F8 11111000 Timing Clock F9 11111001 Undefined FA 11111010 Start FB 11111011 Continue FC 11111100 Stop FD 11111101 Undefined FE 11111110 Active Sensing FF 11111111 System Reset System Exclusive messages address devices by manufacturer. This allows you to send functions that are only related to that particular device and are not common MIDI messages. For example, custom patches for a particular synthesizer (brand and model) can be saved in SysEx at the beginning of a sequence and loaded back into that same brand and model

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of synth at another studio. Another example, you could send all your parameter settings of a MIDI device into patch editing software (editor/librarian) in order to use the computers GUI to make changes to these parameters, rather than using the devices front panel LCD. Each manufacturer has their own SysEx ID number that has been assigned to them by the MMA (MIDI Manufacturers Association).

This ends the Protocol section of MIDI and believe it or not, this is just an overview, barley scratching the surface of the MIDI protocol. Now we’ll talk about the hardware. 2. Hardware Interface

• The MIDI Hardware interface is an opto-isolated, UART (Universal Asynchronous Receive/Transmit) device that transmits data in a Serial fashion (1 bit at a time) at a rate of 31.25 kBaud per second. The UART converts serial-to-parallel when receiving data, or parallel-to-serial when transmitting data.

• The opto-isolator connected to the UART prevents any electrical

connection between units. Data is transferred using an LED (light emitting diode) and a photo-optic cell built into the opto-isolator.

The MIDI connectors are 5-pin DIN plug type. You can find the same type of male plug at both ends of the cable. All MIDI equipped devices use female 5-pin DIN.

• The cables are a twisted pair with a shield for noise rejection. The shield

is only grounded on one side so as not to create a noisy ground loop between instruments.

• Only pins 4 and 5 carry data. Pin 2 is the shield and is grounded only to

the MIDI out connection of a unit. Pins 1 and 3 are not used at this time for MIDI 1.0 spec but may be used at a later date if there is a major revision to the MIDI spec.

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• MIDI is transmitted in a serial fashion (1-bit at a time) at 31.25 kBaud

(31,250 bits per second). Since a MIDI byte is really 10-bits, it takes 320 microsecond to transmit a 10-bit word (31,250/10=3,125 1/3,125=.00032). So a typical 3byte message takes 960 microseconds, or about 1millisecond to transmit.

Typical MIDI Setup Configurations

At its most basic level, MIDI lets the user tie in one synthesizer

with another so that both can be played from the same keyboard. One is the transmitter, or master, generating information that is understood by the second synth, the receiver, or slave.

Synth A - Master Synth B – Slave

For instance, when you play Synth A’s keyboard, the sound of Synth B can be layered along with Synth A. But when you play Synth B’s keyboard, you will only hear Synth B.

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Daisy-Chain Network

The MIDI Thru connector receives a copy of any digital message coming

into the MIDI In connection and sends a duplicate of this information out of the MIDI Thru port into the MIDI In of a third MIDI device. This allows the user to have more than two MIDI devices connected at once. The MIDI Out port from the second or third device in the diagram below would not work because it is sending MIDI information from that particular synthesizer. The MIDI Thru port is receiving the MIDI In information and passing it on to the next device.

When MIDI devices are linked together by a series of MIDI In and MIDI Thru connections, it is referred to as a Daisy-Chain Network.

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In the next example we have added a computer and MIDI interface. The first order of business is to connect the master keyboard to the computer so they can communicate with each other.

Next connect the three tone generators (synthesizers without keyboards)

The MIDI Out on the MIDI interface may also act as a MIDI Thru that relays a copy of the MIDI In information. This will allow the keyboard to communicate with the computer and the three tone generators. Use the concept of the daisy-chain network set-up from the MIDI Thru port of the keyboard.

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One of MIDI’s limitations is that daisy-chaining becomes impractical with more than four instruments. MIDI transmission is pretty fast, 31.25kBaud (31,250 bits per second), but because it is transmitting in a serial fashion (1 bit at a time) instead of a parallel fashion (1 byte at a time), it can get bogged down. After 4 connections, a perceptible time delay can occur. To remedy this effect, a star network is used.

Multi-Port Star Network

A multi-port Star Interface receives MIDI data at the MIDI In ports and then copies the information and sends it out to two or more Thru ports. Each MIDI In port may be assigned to specific MIDI Thru ports. Now we connect the keyboard controller so that it sends information to the MIDI interface.

Then connect the MIDI interface to the Keyboard. Finally, connect the three remaining Tone Generators using a star set-up. Do not use a daisy-chain set-up for these connections.

MIDI Timing Accuracy and Running Status

Since MIDI was designed for musical performance data, it must provide sufficiently accurate timing to preserve the rhythmic integrity of the music. The ear is quite sensitive to small variations in timing that can destroy a musical phrase. This is particularly true for grace notes, strummed chords and clusters of notes, and for rhythmically complex and syncopated music.

Latency (the delay between when an event is triggered and when the resulting sound occurs) is also important: musical instruments feel more and more sluggish to play as latency increases. Since sound travels at about 1 ms per foot, latency of

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7 ms is roughly equal to the maximum separation between members of a string quartet. In practice, latency of 10 ms is generally imperceptible, as long as the variation (due to bottleneck of MIDI data) in the latency is kept small.

With a data transmission rate of 31.25 kBaud, and 10 bits transmitted per byte of MIDI data, a 3-byte Note On or Note Off message takes about 1 ms (960microsec) to be sent. Since MIDI data is transmitted serially, a pair of musical events which originally occurred at the same time but must be sent one at a time in the MIDI data stream and cannot be reproduced at exactly the same time. Luckily, human performers almost never play two notes at exactly the same time. Notes are generally spaced at least slightly apart. This allows MIDI to reproduce a solo musical part with quite reasonable rhythmic accuracy.

However, MIDI data being sent from a sequencer can include a number of different parts. On a given beat, there may be a large number of musical events that should occur virtually simultaneously - especially if the events have been quantized. In this situation, many events will have to “wait their turn” to be transmitted over MIDI. Worse, different events will be delayed by different amounts of time (depending on how many events are queued up ahead of a given event). This can produce a kind of progressive rhythmic “smearing” that may be quite noticeable. A technique called “running status” is provided to help reduce this rhythmic “smearing” effect by reducing the amount of data actually transmitted in the MIDI data stream.

Running status is based on the fact that it is very common for a string of consecutive messages to be of the same message type. For instance, when a chord is played on a keyboard, ten successive Note On messages may be generated, followed by ten Note Off messages. When running status is used, a status byte is sent for a message only when the message is not of the same type as the last message sent on the same Channel. The status byte for subsequent messages of the same type may be omitted (only the data bytes are sent for these subsequent messages).

The effectiveness of running status can be enhanced by sending Note On messages with a velocity of zero in place of Note Off messages. In this case, long strings of Note On messages will often occur. Changes in some of the MIDI controllers or movement of the pitch bend wheel on a musical instrument can produce a staggering number of MIDI Channel voice messages, and running status can also help a great deal in these instances.

So most modern MIDI hardware (e.g. synths) and software use 'running-status'. It's assumed that, once the expected number of data-bytes has been sent/received, IF the next byte is *not* a status-byte, THEN the last status-byte received should be used to decipher the following data bytes. Typically this results in about a 1/3 reduction in the number of bytes sent.

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3. MIDI File Formats

For pure live real-time performance using MIDI systems there is no need for file formats since nothing is being saved. However, if the MIDI data is to be stored as a data file, and/or edited using a sequencer, then some form of "time-stamping" for the MIDI messages is required.

When you record MIDI into a sequencer program, it saves the data as a proprietary format that can only be read by the same or similar program. In other words, if you do a MIDI project in Reason and try to open it on another computer using Reason it should open without any problems and all of your settings and sounds should be there as well. But if you try to open it in another application like cubase or Pro Tools, it won’t open since it wasn’t created on that application. There is a way to get around this obstacle making it possible to save MIDI performance data and have it compatible with practically every sequencing program out there.

The Standard MIDI Files specification provides a standardized method for handling time-stamped MIDI data. This standardized file format for time-stamped MIDI data allows different applications, such as sequencers, scoring packages, and multimedia presentation software, to share MIDI data files.

The specification for Standard MIDI Files defines three formats for MIDI files. MIDI sequencers can generally manage multiple MIDI data streams, or "tracks". Standard MIDI files using Format 0 store all of the MIDI sequence data in a single track. Format 1 files store MIDI data as a collection of tracks. Format 2 files can store several independent songs in a series of Format 0 files. Format 2 has never really caught on and is generally not used by anyone. Most sophisticated MIDI sequencers can read either Format 0 or Format 1 Standard MIDI Files. Format 0 files may be smaller, and thus conserve storage space. They may also be transferred using slightly less system bandwidth than Format 1 files. However, Format 1 files may be viewed and edited more directly, and are therefore generally preferred.

Before we go further with file formats, this would be a good time to talk about an addendum to the MIDI protocol that revolutionized the MIDI industry in the early 90’s. During this time, desktop musicians, multimedia producers, and game developers began clamoring for some level of playback predictability during the exchange of Standard MIDI Files (SMFs). Understandably, composers and arrangers wanted to ensure that piano parts would be played with piano patches and drums wouldn't sound like violins.

General MIDI 1

In the mid ‘80s, Roland produced a sound module called the MT-32. While its sound quality was less than stellar, the MT-32 filled a need for an inexpensive tone module that

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could be MIDI’ed up to a computer to play back sequences for trade show presentations and video games. Roland repackaged the MT on a PC card called the LAPC-1 and sold quite a few. This helped to spawn the idea of GM.

In the late 80’s, MIDI manufacturers saw that there was a huge, untapped market out there at the consumer level. Computer games were becoming very popular and there was a need to standardize music and sound effects. Business multi-media presentations and amateur musicians using MIDI software to compose music all needed a way to standardize MIDI music so that it would sound practically the same on any instrument that it was played back on. This led to the idea of General MIDI.

The first GM module was the Roland SC-55 Sound Canvas. It did very well so other manufacturers all started producing GM compatible equipment. It is now the standard for all computer sound cards and most high-end synths have at least a bank of GM sound in their factory presets. General MIDI or GM is a specification for synthesizers that imposes several requirements beyond the MIDI standard. While MIDI itself provides a protocol which ensures that different instruments can interoperate at a fundamental level (e.g. that pressing keys on a MIDI keyboard will cause an attached MIDI sound module to play musical notes), General MIDI (or GM) goes further in two ways: it requires that all GM-compatible instruments meet a certain minimal set of features, such as being able to play at least 24 notes simultaneously (polyphony), and it attaches certain interpretations to many parameters and control messages which were left unspecified in MIDI, such as defining instrument sounds for each of 128 program numbers.

General MIDI was first standardized in 1991 by the MIDI Manufacturers Association (MMA) and the Japan MIDI Standards Committee (JMSC), and has since been adopted as an addendum to the main MIDI standard.

To be GM1 compatible, a GM1 sound-generating device (keyboard, sound module, sound card, software program or other product) must meet the General MIDI System Level 1 performance requirements outlined below, instantaneously upon demand, and without additional modification or adjustment/configuration by the user.

Voices: A minimum of either 24 fully dynamically allocated voices are available simultaneously for both melodic and percussive sounds, or 16 dynamically allocated voices are available for melody plus 8 for percussion. All voices respond to velocity.

Channels: All 16 MIDI Channels are supported. Each Channel can play a variable number of voices (polyphony). Each Channel can play a different instrument (sound/patch/timbre). Key-based percussion is always on MIDI Channel 10.

Instruments: A minimum of 16 simultaneous and different timbres playing various instruments. A minimum of 128 preset instruments (MIDI program numbers) conforming to the GM1 Instrument Patch Map and 47 percussion

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sounds that conform to the GM1 Percussion Key Map.

Channel Messages: Support for continuous controllers 1, 7, 10, 11, 64, 121 and 123; RPN #s 0, 1, 2; Channel Pressure, Pitch Bend.

Other Messages: Respond to the data entry controller and the RPNs (Registered Parameter Number) for fine and course tuning and pitch bend range, as well as all General MIDI Level 1 System Messages.

General MIDI is limited to the quality of each sound source that it is played back on. Cheaper sound cards may conform to the GM standard but the quality might be drastically inferior to a higher end product.

The advent of GM spawned a whole new market of music programmers that would record MIDI sequences of popular music in GM format and sell them to the amateur, semi/pro and pro musicians for use in live performance.

General MIDI 2

General MIDI 2 was adopted in 1999 and added some significant improvements to the GM1 standard.

32 note polyphony

MIDI ch10 and 11 can simultaneously play percussion sounds.

256 program sounds. Basically, it’s just more variations of the original 128.

GM2's introduction of Key-Based Instrument Controllers is a major step forward in drum programming. Key-Based let’s you change the sound, pan and volume of individual drums instead of just the whole kit.

MIDI on the Web

When it comes to putting your music on the Web, there are two options: posting either audio files or MIDI files. With MIDI files you don’t control the final output of the MIDI file on the user’s system, and since each system is different, the sound quality (as well as the sounds themselves) might vary widely from system to system. There are options that might help limit this uncertainty. Among those are downloadable sounds (DLS) and extensible music format (XMF) files.

DLS DownLoadable Sounds

DLS provides a means for game developers and composers to add their own custom sounds to the GM sound set stored in a sound card's ROM. DLS-compatible devices will automatically download these custom sounds from the SMF disk or internet into

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system RAM, allowing MIDI music to be freely augmented with new instrument sounds, dialog or special effects - thus providing a universal interactive playback experience, along with an unlimited palette of sounds. At the same time, it enables the wavetable synthesizers in computer sound cards to deliver improved audio at no additional cost.

DLS enables the author to completely define an instrument by combining a recorded waveform with articulation information (Attack transients). An instrument defined this way can be downloaded into any hardware device that supports the standard and then played like any standard MIDI synthesizer. Together with MIDI, it delivers a common playback experience, unlike GM, an unlimited sound palette for both instruments and sound effects and true audio interactivity, unlike digital audio.

XMF – Extensible Music Format

XMF is a family of music-related file formats created and administered by the MIDI Manufacturer's Association in conjunction with Beatnik. XMF is based on the idea of containing one or more existing files – such as Standard MIDI Files, DLS instrument files, WAV or other digital audio files, etc. – to create a collection of all the resources needed to present a musical piece, an interactive web page soundtrack, or any other piece of media using pre-produced sound elements. This file format is actually a meta format – a container file that points to other types of files. It loads up the GM SMF and opens the XMF player (Quicktime, Window Media Player) while downloading any digital audio. As soon as it has enough information to start playback, it begins to play the content. In the case of XMF files, the content is usually a MIDI file with its associated files: DLS and other digital audio.