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Learning Center | Midi Simplified

This is addressed to those of you who are completely new getting into this MIDI stuff.
Before you decide to go through this, you may want to start by reading this article first.

The first misconception about MIDI is that MIDI does not carry audio signal like most cables do.

You are not going to be able to record audio into your computer via MIDI cables. Even though there are MIDI connectors in the back of certain audio devices you may have like Guitar Fx processors, digital recorders, drum machines etc., but they are there for a different purpose than sound.

Remember that MIDI has many functions but the one thing that MIDI does that you are interested to learn first is note information.

My best metaphor for MIDI note information is that a MIDI file is like the piece of music, not the music itself. It could be written for piano but played with an organ. MIDI is not the music itself, it is the information for the music.

 

A MIDI file can be played back in three different ways:

•It can be played back by the very keyboard you are using to write the MIDI file in the first place

It can be played back by the Wavetable sounds of your Windows computer's built-in sound card

•It can be played back by a multitude of available software that can emulate instruments in your computer including QuickTime musical instruments.

 

Know your hardware

There are many types of keyboards but most are equipped with MIDI connectors and more recently some have a built -in USB MIDI interface conveniently avoiding the need for an external MIDI interface to connect with the computer.

Some keyboards are mult-timbral and some aren't. A multi-timbral keyboard means that it's capable of playing up to 16 sounds simultaneously. This is the kind of keyboard you would want to have to play back a full arrangement. Consult your manual to find out about the MIDI capabilities of your keyboard if your not sure.


If you see this symbol on your keyboard
:

you can be pretty sure that you have a multi-timbral keyboard.

 

 

Some other keyboards are mono-timbral like many Home digital pianos or certain stage keyboards. You can always use the latter to record MIDI parts but no matter what, they can only play back one sound at a time.

Some keyboards are called controller keyboards because their only purpose is to send out MIDI information to your computer or other MIDI devices. These keyboards, however, do not produce any sounds. These are typically used to control soft-Synths in your computer.

 

What are MIDI channels?

 

There are 16 MIDI channels all traveling through the same MIDI cable. The purpose of these channels is to "channel" information streams for different instruments like piano, bass, drums etc...

 

What are MIDI tracks?

 

You will find horizontal MIDI tracks in your sequencing software. Each track has to be assigned to a specific MIDI channel but you can have many tracks with the same MIDI channel . Assigning a MIDI track to a channel is like giving it a specific address for its data. For example if you decide to record your piano part on track one, you can assign any channel to this track (1-16) as long as the piano sound on the device that plays it back is set to the same MIDI channel. A cool thing with MIDI is that you can sequence parts for an instrument and have it play by a different one.

 

Sequencing:

 

Unlike recording audio which is a solid block of data, MIDI sequencing is dealing with the individual note events of your music.
An audio file in your software would look like this:

 

 

You can cut, copy and sometimes stretch"chunks of audio", however, if you've made a bad note somewhere in your recording you might as well start over.

On a typical sequencer editing window, your MIDI information will be displayed in one of two choices.

 

The piano Roll view:

 

The notation view:

 

In both editing windows you can select individual notes, move them up and down to change pitch or simply delete them. You can also manually draw note events, change note durations, velocity etc.. . Using the notation window or the piano roll window is simply a matter of choice.

 

The in's and out's of MIDI

Now that we have outlined the general idea, lets go more into the details. Assuming you have a multi-timbral keyboard, let's use X-ray vision to look into one.

 

Most keyboards these days have MIDI connectors in the back labeled as: in, out and sometimes thru. The thru output is connected directly from the MIDI in when you daisy chain more than one device (keyboards) but don't worry about this one for now. As the illustration shows, multi-timbral keyboards can be viewed as a series of 16 modules that can each generate a different sound. Most keyboards have two modes. Roland calls it Patch and Performance, Korg calls it Program and Combi etc.. When you play in the program or patch mode you are only accessing one module playing one sound only. When in the Combi or Performance mode you are accessing up to 16 modules, This is the mode that allows you to create layers of sound, splits, etc. Internally, if you can play a performance sound that is a layer of a piano and strings for example, it means that you are using two of your keyboards modules, one has a piano sound assigned to it and the other a strings sound but both have the same MIDI channel. Your keyboard allows you to assign any sound to any of the modules as well as any MIDI channel from 1 to 16.

When you start involving MIDI connections in and out you have to realize that when you play a note on the keys, you are actually sending a MIDI event to two places at once. One is going to your MIDI output and one is playing your internal sound.
The note that is taking the path to your computer will be converted by a MIDI interface into data your computer can read, pass thru your software to be captured as MIDI recording and then come back to the MIDI input of your keyboard to play its' internal sounds. Because this is a longer journey, the MIDI note arrives to the internal sound module a tiny bit later than the ones that took the short cut. However they both play the same sound at a very short interval called "MIDI echoing"

This is no big deal because it is just a few milliseconds delay but it's enough to make you keyboard sound a little weird, hollow sounding and out of phase. This is not the same as another problem called latency which we'll cover later.
There is an easy fix to eliminate MIDI echoing. Somewhere in the MIDI editing menu of your keyboard you will find a feature that will give you the choice between local on and local off.

 

 

In the figure above we have selected local MIDI off so now the MIDI notes that trigger the internal sounds of the keyboard come only from one place, the computer, eliminating MIDI echoing. At this point you are only sending one MIDI channel to your software directly from the keys but your sequencing software will dispatch the desired MIDI channels to the internal modules.
Lets say you are recording a simple sequence of 3 tracks, a piano part, drum part and bass part. The first step is to assign 3 internal modules of your keyboard one for a piano sound, the other for drums and a third for the bass sound, each set to receive a different MIDI channel , let's say piano is channel 1, drums is channel 2 and bass is 3.
Then you pick 3 tracks in your sequencing software and assign them to MIDI channels 1, 2 and 3. Track one is going to be your piano part, track 2 your drum part and track 3 your bass part. As you play the keys, you can hear each sound by simply selecting any of the 3 tracks on your computer because now your tracks are routing each sound you have set. All you have to do is record your parts.
Remember that if you want, you can have many tracks assigned to channel 2, For example, you may want to create a different track for the snare, the bass drum and all other components of your drum set. Because they are all assigned to MIDI channel 2, they will all play the drum sounds in your keyboard.

 

Other Transmited Midi Data

 

Program numbers and program changes

 

MIDI doesn't process terms like "piano" or "Strings" it knows patches (sounds) by numbers. There are 127 program numbers in the language of midi. This is very convenient when you want your sequencer to remember which sound you use on specific tracks. If your keyboard is set to recieve program change, your software will recall all the right patches automatically when you re-open your song file.

 

Note numbers

 

There are 127 note numbers within a program that correspond to the keys on your keyboards or the pads of your drum machine. The most common use for note numbers relate to drum machines and drum triggers so you can match the correct drum element to the desired pad.

Velocity and after touch

 

Velocity is measured in 127 steps from the lighest touch of your keys to the hardest. This information is encoded in your sequencer and like the notes in your editing window, you can also change it or even draw it. Many modern keyboards have "after touch". On some patches , after playing a note, you can alter it's sound by pressing even further to produce a variety of effects like vibrato, bending etc..Like velocity, after touch comes in 127 increments and is encoded by your sequencer.

 

Controllers

 

There are 127 midi controller numbers performing many different remote functions. The most common functions are: volume, pan ,and modulation. These controllers alllow features like Midi mixing where you can mix the midi volume of each instruments in your sequencer, same goes for panning. Again these parameters work in 127 increments. Another nifty application of controllers is found on Midi control devices such as the APC 40 or the MPD 18 . these devices allow you to assign knobs of faders to various knobs and faders in your Midi or audio software. The Perfect example is software like Reason or Ableton Live which are loaded with real-time control features.

 

Sync

 

Finally the last function of Midi that you should care about is Midi- sync. This is why you find Midi connectors on devices like audio digital recorders. Because Midi carries also a time code information, you can sync various devices with Midi clock so for example you computer software could start , tempo lock and stop your digital recorder .

 

General Midi and Midi standard file format

We know that any patch (sound or instrument) can be given any program number or Midi channel. Some standard or protocol had to be created in order to maintain a constant format so people could exchange Midi files. When you download a Midi file from the internet in your PC, your wave-table sound bank inside your sound card plays it just like your multi-timbral keyboard would (see previous illustrations). No matter what the song is, you'll hear all the parts play the right instruments because the Midi data uses a specific group of sounds call the General Midi bank.

 

The general Midi or GM bank contains 128 sounds organized into 16 groups. Each of the sounds in this bank is assigned a specific program number you can see a chart of the GM bank here. You'll find that the drum patch is typically on channel 10. Because a drum patch is made up of my different elements like snare drum, hihats etc, there had to be a standard midi map so the bass drum part doesn't play a cymbal sound for example. Unlike program numbers, the drum map is mapped by note numbers. See GM drum mapping chart here.

 

"Standard midi file" is a non-device specific format for GM files. The extension of a SMF is (.mid) it can be played by any device supporting this file format. Many current keyboards support SMF and a typical application would be to download a SMF from the internet and load it into your keyboard with a floppy disk or other media.

 

NOTE: GM is usually not the bank of choice for professionals. Keyboard Manufacturers do not assign a lot of ROM memory for the GM bank as they do for the rest of the sounds. The piano sound in a GM bank will not sound as stellar as the featured ROM heavy Grand piano in your keyboard. The Wave table sound GM bank located in the sound card of your PC is also not used for professional applications.

 

Written by Eric Warlaumont

 

 

 

 

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