Computers & Midi Sequencing

Computers & MIDI Sequencing – Section One

A computer is an electronic machine that performs complicated calculations very rapidly and is capable of storing and retrieving information. Below is a diagram to show a standard computer system:

Input Process Output

A computer system uses a binary counter to process information. Binary is the language used by computer and consists of 1’s and 0’s. Below a table shows part of the binary counter and the way it is basically used:

When a computer is switched on, many processes are initiated before you begin to give the computer any commands. First the bios is operated which is part of the motherboard and basically says ‘I’m alive’. The rest of the motherboard then comes to life starting with DOS which is a program that recognizes what is connected to the computer, the operating system which includes the GUI (Graphic User Interface) and of course the ROM and RAM memory.

What is MIDI?

MIDI stands for Musical Instrument Digital Interface. Mostly, MIDI is an extensive set of "musical commands" which electronic instruments use to control each other. The MIDI instruments pass these commands to each other over the cables connecting their MIDI jacks together. A MIDI command consists of a few (usually 2 or 3) "data bytes" (like the data bytes within files that you have on your computer's hard drive). These data bytes are merely a series of numbers. We refer to one of these groups of numbers as a "message" (rather than a command). There are many different MIDI messages, and each one correlates to a specific musical action. For example, there is a certain group of numbers that tells an instrument to make a sound. There is a different group of numbers that tells an instrument to stop making a sound. One of the numbers within that "Note On" or "Note Off" message tells the instrument which one of its "keys" (i.e., notes) to start or stop sounding.

There are separate jacks for incoming MIDI signals (received from another instrument that is sending MIDI signals), and outgoing MIDI signals (i.e., MIDI signals that the instrument creates and sends to another device). The jacks look like these:

You use MIDI cables to connect the MIDI jacks of various instruments together, so that those instruments can pass MIDI signals to each other. You connect the MIDI OUT of one instrument to the MIDI IN of another instrument, and vice versa. For example, the

following diagram shows the connection between a computer's MIDI interface and a MIDI keyboard that has built-in sounds.

Some instruments have a third MIDI jack labeled "Thru". This is used as if it was an OUT jack, and therefore you attach a THRU jack only to another instrument's IN jack. ...

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following diagram shows the connection between a computer's MIDI interface and a MIDI keyboard that has built-in sounds.

Some instruments have a third MIDI jack labeled "Thru". This is used as if it was an OUT jack, and therefore you attach a THRU jack only to another instrument's IN jack. In fact, the THRU jack is exactly like the OUT jack with one important difference. Any messages that the instrument itself creates (or modifies) are sent out its MIDI OUT jack but not the MIDI THRU jack.

But MIDI is more than just "Note On" and "Note Off" messages. There are lots more messages. There's a message that tells an instrument to move its pitch wheel and by how much. There's a message that tells the instrument to press or release its sustain pedal. There's a message that tells the instrument to change its volume and by how much. There's a message that tells the instrument to change its ‘patch’ (i.e., maybe from an organ sound to a guitar sound). And of course, these are only a few of the many available messages in the MIDI command set.

And just like with Note On and Note Off messages, these other messages are automatically generated when a musician plays the instrument. For example, if the musician moves the pitch wheel, a pitch wheel MIDI message is sent out of the instrument's MIDI OUT jack. What with all of the possible MIDI messages, everything that the musician did upon the first instrument would be echoed upon the second instrument. It would be like he had two left and two right hands that worked in perfect sync.

You can attach a MIDI cable from the second instrument's MIDI THRU to a third instrument's MIDI IN, and the second instrument will pass onto the third instrument those messages that the first instrument sent. Now, all 3 instruments can play in unison.

You could add a fourth, fifth, sixth, etc, instrument. We call this ‘daisy-chaining’ instruments. Daisy-chained instruments don't always have to play in unison either. Each can play its own, individual musical part even though all of the MIDI messages controlling those daisy-chained instruments pass through each instrument. How is this possible? There are 16 MIDI "channels". For example, that MIDI message for the middle C note can be sent on channel 1. Or, it can be sent on channel 2, etc.

Why use MIDI?

There are two main advantages of MIDI – it's an easily manipulated form of data, and also it produces relatively small data files.

Because MIDI is a digital signal, it's very easy to interface electronic instruments to computers, and then do things with that MIDI data on the computer with software. For example, software can store MIDI messages to the computer's disk drive. Also, the software can playback MIDI messages upon all 16 channels with the same rhythms as the human who originally caused the instruments to generate those messages. So, a musician can digitally record his musical performance and store it on the computer. He does this by "recording" the MIDI OUT of all of his instruments.

Remember that the MIDI messages for all of those instruments go over one run of cables, so if you put the computer at the end, it "hears" the messages from all instruments over just one incoming cable. The great advantage of MIDI is that the "notes" and other musical actions, such as moving the pitch wheel, pressing the sustain pedal, etc, are all still separated by messages on different channels. So the musician can store the messages generated by many instruments in one file, and yet the messages can be easily pulled apart on a per instrument basis because each instrument's MIDI messages are on a different MIDI channel. In other words, when using MIDI, a musician never loses control over every single individual action that he made upon each instrument, from playing a particular note at a particular point, to pushing the sustain pedal at a certain time, etc. The data is all there, but it's put together in such a way that every single musical action can be easily examined and edited.

What is a Sequencer?

A sequencer program "plays" musical performances. It tells equipment that can make musical sounds (i.e. play pitches, chords, or make any kind of noise) what musical notes to play and when to play them. It does this using MIDI messages.

Most sequencers allow a musician to record his performance into the sequencer just as if he were recording his performance upon a cassette tape. The sequencer records MIDI messages instead of the actual sounds. In other words, the sequencer electronically records all of your movements. It does this by storing all of the MIDI messages, which the electronic musical instrument generates when you physically play that instrument.

The sequencer also keeps track of a "musical beat" during the recording so that it can record the "rhythm" of your movements. Usually, the sequencer generates a metronome sound, which the musician follows during the recording phase in order to have the sequencer accurately capture his rhythms while it is storing the generated MIDI messages.

Then, upon playback, the sequencer plays the instrument (that you just did) by electronically recreating all of your gestures. The sequencer does this by sending back (to that instrument's MIDI IN jack) those MIDI messages that the musical instrument generated when you played it. The sequencer doesn't have fingers, so it may send a MIDI message that tells an electronic keyboard to pretend that a human has just pressed middle C for example. The keyboard then sounds middle C.

The advantages of using a sequencer are that the programs usually offer the ability to edit and manipulate the recorded music by changing the tempo, transposing the parts, but the most useful is the ability to edit your performance note by note.

Most computers have software programs, which turn the computer into a sequencer. With a sound card installed inside of the computer, the sequencer can playback musical performances without even needing external MIDI sound modules. Examples of sequencer software are CakeWalk, Cubase, Logic, etc. There are many such programs, as sequencers are perhaps the most often used tools in music production.

An example of a very simple sequencer is Windows Multimedia Player. This software does not have any facility to record MIDI messages, nor edit them. It can only playback a MIDI performance (stored in MIDI File Format). Such simple "playback only" sequencers are often called "MIDI Players".

The Significance of MIDI Sequencing

MIDI sequencing makes it possible for a composer to hear his arrangement played without needing other musicians. It thereby frees the composer from scheduling problems, and allows him more opportunity to audition his composition during the composition process, which provides invaluable feedback to aid in composition. It also makes it easier for composers to hear difficult–to–execute music. It is often easier to have a computer play a difficult performance than it is to find a musician capable of playing that performance. Likewise, it is often easier to have a computer play esoteric music (i.e. unusual instrumentation) than find musicians who have appropriate skills and the desire to play that music.

MIDI sequencing allows for more efficient recording sessions by improving the process of correcting mistakes in the recording, and streamlining the recording process itself. They eliminate the need to have an engineer with special skills, as the computer takes over some of those functions, such as "punching in" overdubs. And they also offer efficient ways to make useful changes, such as transposing key.

There would be no way for professional recordings to be made on a budget, in small, "home" environments that don't require things like special soundproofing without the use of MIDI. Furthermore, the technology in computer audio often eliminates expensive, time-consuming tasks, such as tuning drum kits and placing microphones and cables. The storage capacity of computers also makes recalling a given setup very efficient and inexpensive, which is important since often a setup needs to be recalled during multiple sessions.