1. Audio Engineering
Audio engineering is a part of audio science dealing with the recording and reproduction of sound through mechanical and electronic means.
An audio engineer must be proficient with different types of recording media, such as analog tape, digital multi-track recorders and workstations, and computer knowledge.
In this digital age, an audio engineer requires to be well-versed with the overall understanding of software and hardware integration and analog-digital audio transfers.
Let us take on a topic that has been of immense help and utmost importance to audio engineers around the globe!

2. MIDI
MIDI (Musical Instrument Digital Interface); is an industry-standard protocol that enables electronic musical instruments and other equipment to communicate, control and synchronize with each other and to exchange system data
Devices such as computers, synthesizers, keyboard controllers, sound cards, samplers and drum machines
MIDI does not transmit an audio signal or media!
The sounds are generated by the synthesizer, which receives the MIDI data
MIDI (Musical Instrument Digital Interface) is an industry-standard protocol that enables electronic musical instruments and other equipment to communicate, control and synchronize with each other and to exchange system data.
It is an opto-isolated serial interface and communication protocol. MIDI data is in serial binary form (i.e. 1’s and 0’s, known as bits) and is transmitted between devices via a single data cable.
Devices such as computers, synthesizers, keyboard controllers, sound cards, samplers and drum machines.
It provides for the transmission from one device or instrument to another of real-time performance data.
MIDI does not transmit an audio signal or media! It is important to remember that MIDI does not send sounds; rather it sends instructions on how the sounds are to be performed. It only transmits event messages such as the pitch and intensity of musical notes to be played. Control signals for parameters such as volume, vibrato and panning, and clock signals to set the tempo.
The sounds are generated by the synthesizer, which receives the MIDI data.
The electronic protocol is widely used throughout the music industry.
(Click on audio button for nokia tune)

3. Interfacing
The original physical MIDI connection uses DIN 5/180° connectors.
Simply put, 5 pins occupying 180° or half of the circular connector.
Interestingly, the connector is an earlier version of the PS-2 or mini-DIN connectors, which we use nowadays for keyboards and mice!
Opto-isolating connections are used, to prevent ground loops occurring among connected MIDI devices.
The traditional MIDI cable used is a shielded twisted pair.

4. MIDI Ports
MIDI-In Port allows data to be received by a MIDI-compliant device
MIDI-Out Port is used for transmitting data
MIDI-Thru Port is used for linking a no. of MIDI devices with a single transmitter
The MIDI port is the logical and/or physical connection, through which MIDI devices communicate with one another.
MIDI-In Port allows data to be received by a MIDI-compliant device. The In-port is how a MIDI synthesizer is controlled by an external device or sequencer.
MIDI-Out Port is used for transmitting data.
MIDI-Thru Port is used for linking a no. of MIDI devices with a single transmitter. Data that comes out of a device's MIDI-Thru port is an exact duplicate of the data received at the MIDI-In port and has not been generated on the device’s MIDI-Out port.

5. The MIDI IN connector is supposed to have the opto-isolator and no ground connection to pin 2 or to the shield for the express purpose of avoiding a ground loop.
Ground loops will cause horrendous hum, buzzes, and other noises, especially when connected to computerized gear or lighting equipment.
The noises are caused by differences in voltage potential from one end of the cable to the other.
This is done by using a balanced current loop through an opto-isolator and only grounding the MIDI outputs.

6. MIDI Thru
MIDI-Thru Port repeats the data that is received by the MIDI-In port; i.e. the incoming data is retransmitted over the MIDI-Thru port, therefore a no. of other devices can be linked.
The musician controls the primary keyboard. The primary-keyboard's MIDI-Out port controls the secondary keyboard. The secondary keyboard is also configured to pass-through incoming commands to the MIDI-Thru port, which controls the tertiary keyboard. Hence, the musician is able to control two additional keyboards via a single MIDI-Out port.

7. New Interfacing methods
All MIDI compatible instruments have a built-in MIDI.
Some computers' sound cards have a built-in MIDI, whereas others require an external MIDI which is connected to the computer via the USB connector or by FireWire.
Due to the increasing use of computers for music-making and composition and increased use of USB connectors, companies began making USB-to-MIDI audio interfaces, while MIDI keyboard controllers were equipped with USB jacks.

8. Networks
A MIDI network is a combination of hardware and software that provides interconnectivity between a group of MIDI devices, such as synthesizers, controllers, and sequencers. The concept of the MIDI network is just a generalization of a device called the Patch Bay. Originally, a "patch bay" module consisted of a MIDI-In connector and multiple MIDI-Out connectors. A MIDI network may contain one or more logical MIDI ports that interconnect dozens of MIDI devices.
A MIDI network is a combination of hardware and software that provides interconnectivity between a group of MIDI devices, such as synthesizers, controllers, and sequencers

9. Protocol MIDI is a serial stream of data
Runs at bits per second baud rate
Describes event information
Asynchronous transmission
A 'standard' MIDI word consists of three bytes: The first is a Status byte, the second and third are Data bytes
All status bytes have their MSB set to 1, whereas all data bytes have it set to 0
MIDI is a serial stream of data and runs at bits per second baud rate. It is used to describe when a note is pressed, which note it is, how hard and for how long, but not the sound that is created by this action.
The transmission of MIDI messages is asynchronous, i.e. is not constant or only occurring when a message is sent from a device.
A 'standard' MIDI word consists of three bytes, though depending on use it may have more or less, generally though. The first is a Status byte, the second and third are Data bytes.
So, with a stream of data coming in, how do you know which byte is which? And which byte is for what? This will be answered later… Hang on.
All status bytes have their MSB set to 1, whereas all data bytes have it set to 0.

10. Messages
MIDI messages commonly have at least one COMMAND\STATUS byte and may have zero or more DATA bytes
Types of Messages:
Channel Messages
System Exclusive Messages
System Common Messages
System Real-Time Messages
MIDI messages commonly have at least one COMMAND byte and may have zero or more DATA bytes.
We can categorize MIDI messages into the following categories: 
1. Channel Messages
2. System Exclusive Messages
3. System Common Messages
4. System Real-Time Messages 

11. Channel Messages Message Name Byte 1 Byte 2 Byte 3 Example Note Off
1000 cccc
The MIDI key specifies the number of the key or note to release.
The velocity specifies how quickly the note- release is affected.
83 3D 79 turns note 3D (decimal 61) on channel 3 off with a velocity of 79 (decimal 121).
Note On
1001 cccc
The MIDI key specifies the number of the key or note to turn on.
The velocity specifies how quickly or forcefully the note is struck.
94 3D 79 turns note 3D (decimal 61) on channel 4 on with a velocity of 79 (decimal 121).
Polyphonic Aftertouch
1010 cccc
The MIDI key number.
The key pressure value.
A0 3D 5A changes the pressure for note 3D (decimal 61) on channel 0 to a value of 5A (decimal 90).
Control Change
1011 cccc
The controller number [ ]
The controller value [ ]
B3 10 7F sets the value of controller number 10 (decimal 16) to 7F (decimal 127).
Program Change
1100cccc
The new program (patch) number.
-- n/a --
C3 44 changes the program number for MIDI channel 3 to 44 (decimal 68).
Channel Pressure (Aftertouch)
1101 cccc
The single greatest pressure value of all depressed keys.
D3 44 changes the channel-pressure for MIDI channel 3 to 44 (decimal 68).
Pitch Wheel Change (Pitch Bend)
1110 cccc
Least significant 7- bits of pitch-bend value.
Most significant 7-bits of pitch-bend value.
E sets the pitch-bend for channel 1 to a value of 03F8 (decimal 1016).
Channel Messages
Channel messages are used for controlling one or more of the 16 MIDI channels or for controlling musical notes using a specific MIDI channel. There are only 16 MIDI channels per logical MIDI-Port or connection.
Channel messages are the primary messages used for controlling synthesizers and for receiving input from MIDI controllers. Channel messages require two or three bytes, depending on the specific message. The first byte is always divided into two nibbles (4-bits). The first nibble contains the message number, and the second nibble contains the channel number. Channels have a value between 0 and 15.

12. System Exclusive Messages
System Exclusive Messages are generally longer MIDI messages that are used for a variety of purposes
One of the primary purposes of the SysEx message is to send manufacturer-specific data to a MIDI synthesizer
Each SysEx message begins with two data bytes F0 ( ) and 0iiiiiii, where iiiiiii is a manufacturer's code and equipment only responds to messages with the correct manufacturer's code
The SysEx message is terminated when the byte value F7 ( ) is encountered
System Exclusive Messages: One of the primary purposes of the SysEx message is to send manufacturer-specific data to a MIDI synthesizer.
The system-exclusive (SysEx) message is just a message-shell for transporting data and commands that are not supported by the MIDI specification.
Each SysEx message begins with two data bytes F0 ( ) and 0iiiiiii, where iiiiiii is a manufacturer's code. Each equipment manufacturer has its own unique code and the equipment only responds to messages with the correct manufacturer's code.
The SysEx message is terminated when the byte value F7 ( ) is encountered.

13. System Common Messages
Message Name
Byte 1
Byte 2
Byte 3
System Exclusive
F0 ( )
The manufacture's unique identifier.
-- n/a --
Reserved
F1 ( )
Song Position Pointer
F2 ( )
Least significant 7-bits.
Most significant 7-bits.
Song Select
F3 ( )
The song or sequence to be played.
F4 ( )
F5 ( )
Tune Request
F6 ( )
System Exclusive END
F7 ( )
System Common Messages provide some standardized features that are used for controlling the playback of songs in MIDI format and some other miscellaneous features.
System-common messages are a bunch of messages that are used for purposes other than controlling MIDI voices and channels. All System-common messages have the first nibble of the first byte equal to F (i.e., 1111).

14. System Real-Time Messages
Message Name
Byte 1
Byte 2
Byte 3
Timing Clock
F8 ( )
-- n/a --
Reserved
F9 ( )
Start
FA ( )
Continue
FB ( )
Stop
FC ( )
FD ( )
Active Sensing
FE ( )
Reset
FF ( )
System Real-Time Messages provide some MIDI features for synchronizing the internal timing clocks of connected MIDI devices and for controlling the playback of sequences or songs in MIDI format.
System real-time messages are those messages that are system-wide in nature and are used controlling the sequencer in real-time. Like the System-common messages, the real-time messages are defined with the first nibble value of F (1111).
The musical instrument generates these messages autonomously; all the musician has to do is play the notes (or make some other gesture). This consistent, automated abstraction of the musical gesture could be considered the core of the MIDI standard.

15. MIDI Controllers
Amongst MIDI enthusiasts, keyboards and other devices used to trigger musical sounds are called "controllers", because with most MIDI set-ups, the keyboard or other device does not make any sounds by itself. MIDI controllers need to be connected to a voice bank or sound module in order to produce musical tones or sounds; the keyboard or other device is "controlling" the voice bank or sound module by acting as a trigger. It is the human interface component of a traditional instrument redesigned as a MIDI input device.
MIDI controllers are available in a range of forms.
All MIDI compatible controllers, musical instruments, and MIDI-compatible software follow the same MIDI specification, and thus interpret any given MIDI message the same way. For example, if a note is played on a MIDI controller, it will sound at the right pitch on any MIDI instrument whose MIDI In connector is connected to the controller's MIDI Out connector.

16. Example
1. Note-On message: 0x90, 0x3C, 0x7F 2. Aftertouch message(s): 0xD3, 0x46 3. Note-Off message: 0x80, 0x3C, 0x46
Example: When a musical performance is played on a MIDI instrument (or controller) it transmits MIDI channel messages from its MIDI-Out connector.
A typical MIDI channel message sequence corresponding to a key being struck and released on a keyboard is:
1. The user presses the middle C key with a specific velocity (which is usually translated into the volume of the note). The instrument sends one Note-On message.
2. The user changes the pressure applied on the key while holding it down - a technique called Aftertouch. The instrument sends one or more messages.
3. The user releases the middle C key, again with the possibility of velocity of release controlling some parameters. The instrument sends one Note-Off message.
Note-On, Aftertouch and Note-Off are all channel messages.
MIDI is also used for a whole host of other events, but the action of pressing a note is the simplest to describe and understand.
(Show this with the help of Channel messages table)
Let’s take the action of the Note On Event. Three bytes are sent; Status, Note On, Velocity.
Assuming, we're working on Midi Channel 1, the data would look something like this 0x90, 0x3C, 0x7F.
Let’s go through the bytes one at a time.
First the status byte, 0x90 if we translate this into binary we get The upper nibble (1001) shows we have a Note On event, the lower nibble (0000) is the MIDI channel 1. MIDI devices can have 16 channels.
The next byte is the note value, in this case 0x3C, which is the middle C note.
The final byte is 0x7F, which is the velocity i.e. how hard the key was pressed, in this case maximum.
And so on..

17. Composition & File formats
MIDI composition and arrangement typically takes place using either MIDI sequencing/editing software on computers or using specialized hardware music workstations
MIDI data files are much smaller than recorded audio waveforms
The SMF specification was developed and is being maintained by, the MIDI Manufacturers Association (MMA)
Karaoke files display lyrics synchronized with the music in "follow-the-bouncing-ball" fashion, turning any PC into a karaoke machine
MIDI composition and arrangement typically takes place using either MIDI sequencing/editing software on computers or using specialized hardware music workstations.
MIDI data files are much smaller than recorded audio waveforms. Many computer sequencing programs allow manipulation of the musical data such that composing for an entire orchestra of sounds is possible.
MIDI messages (along with timing information) can be collected and stored in a computer file system, in what is commonly called a MIDI file, or more formally, a Standard MIDI File (SMF).
The SMF specification was developed and is being maintained by, the MIDI Manufacturers Association (MMA).
These formats are very compact; a file as small as 10 KB can produce a full minute of music or more due to the fact that the file stores instructions on how to recreate the sound based on synthesis with a MIDI synthesizer rather than an exact waveform to be reproduced. Small MIDI file sizes have also been advantageous for applications such as mobile phone ringtones, and some video games.
Another format called MIDI-Karaoke, which uses the ".kar" file extension displays lyrics synchronized with the music in "follow-the-bouncing-ball" fashion, turning any PC into a karaoke machine.

18. Synthesizer
A synthesizer is an electronic musical instrument that uses one or more sound generators to create waveforms which are then processed and combined in order to generate musical sounds
MIDI synthesizers produce musical tones and percussion based on the input of MIDI software messages
A synthesizer is an electronic musical instrument that uses one or more sound generators to create waveforms which are then processed and combined in order to generate musical sounds.
Early synthesizers were analog hardware based but many modern synthesizers use a combination of DSP software and hardware or else are purely software-based. Endless no. of synthesis can be achieved by algorithms that work on digital signals.
MIDI synthesizers produce musical tones and percussion based on the input of MIDI software messages.
Synthesizers are often controlled with a piano-style keyboard, leading such instruments to be referred to simply as "keyboards". Several other forms of controllers have been devised to resemble violins, guitars and wind-instruments.
Synthesizers without controllers are often called "modules", and can be controlled using MIDI.
With the development of MIDI, it was easier to integrate and synchronize synthesizers and other electronic instruments for use in musical composition.

19. Sequencer
A music sequencer is an application or a device designed to record and play back musical notation
A MIDI sequencer is the electronic version of the musician in the MIDI world
A MIDI sequencer:
records MIDI software message sequences
replays MIDI software sequences with the appropriate timing
provides some sort of editing capabilities
The terms "Music Sequencer" and "Digital Audio Workstation" are often used interchangeably
A music sequencer is an application or a device designed to record and play back musical notation.
With the advent of MIDI, programmers were able to write software which could do the same.
A MIDI sequencer is the electronic version of the musician in the MIDI world.
A MIDI sequencer: (a) records MIDI software message sequences, (b) replays MIDI software sequences using the appropriate timing, and (c) provides some sort of editing capabilities.
We will look into these features on software:
During recording, the sequencer captures and plays back live MIDI performances. Performances can also be constructed slowly, note-by-note, using onscreen pencil tools that let you “draw” the notes you want.
A sequencer may let you view notes in a variety of ways, from a list of MIDI events, to a piano-roll-type view, to onscreen notation. The capturing of MIDI notes is just the beginning, since a sequencer allows you to do all sorts of things to perfect your music.
Some of the most commonly used sequencer tools are:
Quantization - that corrects the timing of notes.
Transposition - that moves notes to new musical keys.
Scaling - that changes the feel of recorded musical phrases by adjusting recorded velocity values, note lengths, and more.
Some sequencers can record audio in addition to MIDI, allowing you to work on all of the elements in a song at the same time.
Hence, the terms "Music Sequencer" and "Digital Audio Workstation" are often used interchangeably, as modern sequencers combine both sets of features.

20. Sampler
A sampler is an electronic musical instrument similar in some respects to a synthesizer but, instead of generating sounds, it uses recordings (or “samples") of sounds that are loaded or recorded into it by the user and then played back by means of a keyboard, sequencer or other triggering device to perform or compose music.
Because these samples are nowadays usually stored in digital memory the information can be quickly accessed.
In general, samplers can play back any kind of recorded audio and most samplers offer editing facilities that allow the user to modify and process the audio and to apply a wide range of effects, making the sampler a powerful and versatile musical tool.
A sampler is an electronic musical instrument which plays back recordings (or “samples") that are loaded or recorded onto it to perform or compose music

21. Software samplers
The increases in computing power and memory capacity have made it possible to develop software applications that provide the same capabilities as hardware-based units.
These are typically produced as plug in instruments - for example, using the VST or Virtual Studio Technology system.

22. MIDI Standards Patch Family Name 1 - 8 Piano 65 - 72 Reed 9 - 16
Chromatic Percussion
Pipe
Organ
Synth Lead
Guitar
89- 96
Synth Pad
Bass
Synth Effects
Strings
Ethnic
49- 56
Ensemble
Percussive
Brass
Sound Effects
General MIDI, or “GM,” is a very specific set of standards that allows MIDI composers and arrangers to create music that always plays correctly on any device that supports General MIDI. GM was developed by the MMA and the Japan MIDI Standards Committee (JMSC) and first published in 1991.
Why Do We Need GM? All General MIDI devices contain the same set of 128 standard sounds and drum kit sounds, stored in a specified order. Each product creates these sounds using its own unique capabilities, but the goal is to have them all sound similar enough when playing back GM data.
Instrument Patch Map in GM: The sounds are grouped into "families" of eight patch numbers each. Patch numbers are in decimal, and start at 1, MIDI patch numbers start at 0.
General Midi 2: In 1999, the official GM standard was updated to include more controllers, patches and SysEx messages. General MIDI 2 was introduced. It included everything in General MIDI 1, adding more sounds, standards for sound editing, and some other niceties. General MIDI 2 was last amended in February 2007.

23. Musical Applications
You can use a MIDI instrument with which you’re comfortable to play the sounds belonging to any other MIDI device.
Create rich musical textures by layering sounds from multiple MIDI devices, or assign different sounds to play in different pitch ranges.
When you play a MIDI instrument, it produces data that can be captured by a MIDI “sequencer.” Sequencers aren’t just MIDI recorders, they let you fix mistakes, change the pitches of your notes, fix their timing, the way they play, the sounds they use, and more.
Musically speaking:
You can use a MIDI instrument with which you’re comfortable to play the sounds belonging to any other MIDI device.
Create rich musical textures by layering sounds from multiple MIDI devices, or assign different sounds to play in different pitch ranges.
When you play a MIDI instrument, it produces data that can be captured by a MIDI “sequencer.” Sequencers aren’t just MIDI recorders, they let you fix mistakes, change the pitches of your notes, fix their timing, the way they play, the sounds they use, and more.
Let us see how this is done!

24. We are using the AVR ATMega128 micro-controller.
It has 4 switches connected to pins PD6, PD7, PE6 & PE7 respectively.
An LCD through PORT A, 8 LED’s connected to PORT C and is running on 16 MHz clock speed.
The program is such that..

25. ATMega128 μC LCD PC UART 1 TX RX LED1 LED2 LED3 LED4 LED5 LED6 LED7
SW1
SW2
SW3 PC TX
Let us have a basic understanding of how the MIDI drum controller works.
UART 1
SW4 RX

26. Sends 0x90, 0x24, 0x7F to PC LCD PC ^ B UART 1 TX RX LED1 LED2 LED3
SW1 ^ B
SW2
SW3 PC TX
UART 1
SW4 RX

27. Sends 0x91, 0x26, 0x7F to PC LCD PC ^ BS UART 1 TX RX LED1 LED2 LED3
SW1 ^ BS
SW2
SW3 PC TX
UART 1
SW4 RX

28. Sends 0x92, 0x31, 0x7F to PC LCD PC ^ BSC UART 1 TX RX LED1 LED2 LED3
SW1 ^
BSC
SW2
SW3 PC TX
UART 1
SW4 RX

29. Sends 0x93, 0x2E, 0x7F to PC LCD PC ^ BSCH UART 1 TX RX LED1 LED2 LED3
SW1 ^
BSCH
SW2
SW3 PC TX
UART 1
SW4 RX

30. Non-musical Applications
Show control
Machine control
Theatre lighting
Console automation
Special effects
Sound design
Recording system synchronization
Audio processor control
Computer animation
Computer networking
Video Jockeys
Non-musical applications: Non-musical applications of MIDI are possible because any device built with a standard MIDI Out connector should in theory be able to control any other device with a MIDI In port, just as long as the developers of both devices have the same understanding about the semantic meaning of all the MIDI messages.
Therefore, MIDI is also used every day as a control protocol in applications other than music, including:
Show control: The protocol simply transmits digital data providing information such as the type, timing and numbering of technical cues called during a multimedia or live theatre performance.
Machine control
Theatre lighting
Console automation: Audio mixers can be controlled with MIDI during console automation.
Special effects
Sound design
Recording system synchronization
Audio processor control
Computer animation
Computer networking
Video Jockeys: Some MIDI devices allow “VJs” or “Video Jockeys” - to manipulate video images onstage, creating exciting visuals. Special software on a laptop computer along with physical controls open up a world of video possibilities, letting VJs remotely select clips and control how they behave.

31. We have come a long way...
HD-MIDI\HD Protocol: Development of a version of MIDI for new products which is fully backward compatible is now under discussion in the MMA. First announced as "HD-MIDI" in 2005 and tentatively called "HD Protocol" since 2008, this new standard would support modern high-speed transports, provide greater range and/or resolution in data values, increase the number of Channels, and support the future introduction of entirely new kinds of messages. Representatives from all sizes and types of companies are involved, from the smallest specialty show control operations to the largest musical equipment manufacturers.

32. References Webistes: Wikipedia (http://en.wikipedia.org/)
How stuff works (
MIDI Manufacturers Association (
MIDI Reference from IO.com(
Tonalsoft (
Books and eBooks:
eBook – MIDI and the AVR – AVRFreaks.com (
Audio Engineering: Know It All - Douglas Self
Audio Electronics, Second edition - John Linsley Hood

33. Thank You
Bhaumik Bhatt