The Musical Instrument Digital Interface MIDI standard defines a communication protocol for electronic music devices, such as electronic keyboard instruments and personal computers. MIDI data can be transmitted over special cables during a live performance, and can also be stored in a standard type of file for later playback or editing.
If you have a thorough understanding of MIDI, you can safely skip this section. MIDI is both a hardware specification and a software specification. To understand MIDI's design, it helps to understand its history. MIDI was originally designed for passing musical events, such as key depressions, between electronic keyboard instruments such as synthesizers.
As mentioned in Chapter 1, MIDI data consists primarily of control events that communicate a musician's gestures. MIDI data doesn't contain the audio that results from these events. Hardware devices known as sequencers stored sequences of notes that could control a synthesizer, allowing musical performances to be recorded and subsequently played back.
Later, hardware interfaces were developed that connected MIDI instruments to a computer's serial port, allowing sequencers to be implemented in software. CPUs have become fast enough that synthesizers, too, can be implemented in software. This portion need not concern us. Because devices that originally required hardware, such as sequencers and synthesizers, are now implementable in software, perhaps the only reason for most programmers to know anything about MIDI hardware devices is simply to understand the metaphors in MIDI.
The software portion of the MIDI specification is extensive. This portion concerns the structure of MIDI data and how devices such as synthesizers should respond to that data. It is important to understand that MIDI data can be streamed or sequenced.
The cable transmits digital data from one MIDI device to another. The different kinds of message are distinguished by the first byte in the message, known as the status byte. Status bytes are the only bytes that have the highest-order bit set to 1. The bytes that follow the status byte in a message are known as data bytes. Certain MIDI messages, known as channel messages, have a status byte that contains four bits to specify the kind of channel message and another four bits to specify the channel number.
Then we can send the notes as already explained. This is often used in practice. There are MIDI controllers defined, but only a few of them are used in practice.
The purpose of a MIDI controller is to set a value of a parameter in the synthesizer playing the notes, like the volume, the panoramic position in space from left to right in stereo , the level of reverberation, The volume change has an impact on all notes currently playing as well as the notes that will start playing later. The synthesizer keeps that volume level until another volume level is sent.
The velocity cannot be changed once the note has been started, so you can use the volume controller to change the level of the note after it has been started. To create a crescendo, you need to send a sequence of increasing volume values.
You must always balance out the velocity and volume values to use, so that both are in a correct range of value. If one of them is too low, the notes may not be heard correctly even if the other value is at its maximal value. The effect of both values are multiplicative to determine the real loudness of the note. As we have seen before, you can select a sound on a synthesizer with the values of the program change message. A synthesizer may contain one or more sound banks, each containing sounds.
If you want to use a specific sound bank of the synthesizer, you must first activate the new bank and then send the program change message. After receiving these messages, the synthesizer will play the following notes with that specific sound.
In practice, only a few are implemented. The information about the program change numbers and the sound banks available is to be found in the MIDI implementation chart and MIDI specifications of the synthesizer you are using.
The message is the following:. The 14 bit value of the pitch bend is defined so that a value of 0x is the center corresponding to the normal pitch of the note no pitch change. Using numbers above 0x up to 0x3FFF will increase the pitch and using numbers below down to 0x will decrease the pitch. The range of pitch change is symmetric up and down and can often be adjusted in the synthesizer itself.
This is usually used as a cheaper alternative to aftertouch, as it requires only one pressure sensor instead of one for each individual key. As I said in the intro, the great thing about recording in MIDI is that it is incredibly easy to edit your recordings after the fact. Select a MIDI note fig 1. Drag its associated velocity to change it figs 2 and 3 change the velocity of a MIDI note from to You can drag on the beginning and end of a MIDI note to lengthen or shorten its duration figs 5 and 6.
I do not even know how I ended up here, but I thought this post was good. Reply 5 years ago. I have just come by an old digital recorder and I'm having similar thoughts I'm having dreams of just being able to pick up a cord at a music shop and plug it straight into the PC so that I could record synth stuff. I can't be sure I wonder why Status byte must start with 1, and the other data bytes must start with 0.
I mean, I read that this is the way the midi reciever recognize each byte. However, that doesn't make sense to me. Why isn't it possible to use values for each data bytes?
What happens in the first values of the Status byte? Reply 6 years ago on Introduction. If something goes wrong, and some bytes are dropped, the device doesn't have to know how many bytes were dropped to know which byte is the start of a message.
Reply 7 years ago on Introduction. I would like to make a midi foot controller that can control an audio switcher for example like this. Amanda, you are an IDOL! Most of the System Real Time messages are normally ignored by keyboard instruments and synthesizers. To help ensure accurate timing, System Real Time messages are given priority over other messages, and these single-byte messages may occur anywhere in the data stream a Real Time message may appear between the status byte and data byte of some other MIDI message.
The Timing Clock message is the master clock which sets the tempo for playback of a sequence. The Timing Clock message is sent 24 times per quarter note. The Start, Continue, and Stop messages are used to control playback of the sequence.
Without Active Sensing, if a cable is disconnected during playback, then some notes may be left playing indefinitely because they have been activated by a Note On message, but the corresponding Note Off message will never be received.
The System Reset message, as the name implies, is used to reset and initialize any equipment which receives the message. This message is generally not sent automatically by transmitting devices, and must be initiated manually by a user. System Exclusive messages may be used to send data such as patch parameters or sample data between MIDI devices.
The manufacturers ID is followed by any number of data bytes, and the data transmission is terminated with the EOX message. Manufacturers are required to publish the details of their System Exclusive data formats, and other manufacturers may freely utilize these formats, provided that they do not alter or utilize the format in a way which conflicts with the original manufacturers specifications.
Certain System Exclusive ID numbers are reserved for special protocols. The www. Log in Login to your account. Log in. Remember Me Forgot your password? Password Reset. Please enter the email address for your account. A verification code will be sent to you. Once you have received the verification code, you will be able to choose a new password for your account. Subscribe to this blog post Unsubscribe. Aftertouch Some MIDI keyboard instruments have the ability to sense the amount of pressure which is being applied to the keys while they are depressed.
Pitch Bend The Pitch Bend Change message is normally sent from a keyboard instrument in response to changes in position of the pitch bend wheel.
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