 Hello, welcome to the session of musical instrument digital interface learning outcome of this session. At the end of this session students will be able to delineate musical instrument digital interface, describe the MIDI computer interface and differentiate between MIDI and digital audio. MIDI, the musical instrument digital interface is nothing but a standard for the communication between the electronic musical instruments. The main function of this protocol is transmission of the performance of or the control data around the digitally controlled music systems and the other data such as timing information, setup parameters and sample. The MIDI standards was founded by the agreement between the manufacturers early in the 80s. Let me ask you one question. What are the examples of the MIDI instruments? You can pause this video, think about this question and write down your answer in the notebook. After writing the answer you can resume the video to see what is the answer. Let me answer the question. The answer is piano, acoustic guitar, violin are some examples of the MIDI instruments. So why to use the MIDI? The old instruments uses analog voltage control instead of the microprocessors. These analog instruments are frequently used for the note triggering pitch information ETC. With the use of the microprocessor based control in the instruments a number of digital control interfaces is appeared. Because of the incompatibility amongst these instruments there is a need of standardization and the agreement between the major manufacturers has been created which is resulted in the MIDI protocol earlier in 1982 to 83. The MIDI manufacturer associations is a governing body for regulating the modifications to the standards. So what is the difference between the MIDI and the digital audio? In case of the digital audio the waveform is converted into the digital domain. That means the analog waveform is sampled and converted into the digital domain. This digital audio is stored into the memory and again back it is converted into the analog and given to the speaker as shown in a diagram. The sounds are stored and replayed precisely but we have no access to control the data. And since we need the high resolution and precise amplitude in order to represent a proper audio the digital audio uses a lot of memory space. Whereas in case of the MIDI instrument we can see here is one piano that one key is pressed the one note is transmitted to the computer. So because of this single note digitization of this single note occupy the very less memory of the computer that is the advantage of the MIDI over the digital audio. So the MIDI hardware comprises of a central processing unit it is nothing but the microprocessor, RAM, ROM and the universal earth synchronous serial communication protocol. There is a control interface available in order to control the data bus address bus. So the MIDI communication takes place by the serially. So the data stream which is needed for the communication is represented as follows. There are 8 bit data with the initial start bit and the stop bit. So the total 10 bit data byte is used for the communication. So in MIDI the binary 0 or 1 is defined by the current flowing or not flowing over the loop. Thus in ideal state the binary 1 the start bit is always 0 and the stop bit always 1. So what is the speed of this transmission? The speed of the MIDI communication is 31.25 kilobits per second. As a reference for USB 1.1 low-speed transmission is at the rate of 1.5 megabots if the USB 2 protocol has a speed of 480 megabots. The MIDI port the MIDI port uses three ports in out and the through. In port is used in order to accept the input to the device the through port is used to amplify the copied input signal and the output is used to transmit the device output. It uses the pin as shown in the figure. This is a 5 pin connector in which the pin number 2, 4 and the 5s are used. The long cable causes the unwanted distortion so the maximum of 15 meter is used or recommended for the MIDI interconnection. So these are the example of the MIDI computer interface. So the figure A shows a MIDI joystick ports. These type of the MIDI joystick ports are used in earlier days. Later on the MIDI USB interface has been innovated. That will provide the maximum feasibility of 16 channels within one USB port or we can call it as a multi-port interface is possible because of this USB MIDI interface. They allow the synchronized handling of the several devices. This is a 32 bit MIDI event packet. The packet is of the size 32 bit. It consists of 4 bytes each byte is of the 8 bit length. The packet it start with the packet header and it is followed by the 3 MIDI event data. The packet header consists of 4 bit cable number and the 4 bit code index number. The cable number is the value which is ranging from 0 to F indicating the assigned number of the embedded MIDI jack associated with the endpoint that is the transferring a data. The code index number indicates the classification of the bytes in the MIDI fields. So the MIDI messages are classified in two types, channel messages and the system messages. The channel messages are further divided into voice messages and mode messages whereas the system messages are further divided into real time, common and a system exclusive messages. Let us see the details of these messages. The voice messages include note on, note off, polyphonic key press, control change, program change, channel press pressure after the touch and the pitch bend where the mode indicates how the device responds to the message on certain channel. A device might be respond to the all MIDI channel which is called as Omnimode or it might instructed to respond for the polyphonic messages or a monophonic messages. The polyphonic messages involve playing more than one note at the same time. The system messages, the system messages are sent to the whole system rather than a particular channel. They can be subdivided into real time, common, system exclusive messages. A system common messages includes tuned requests, song select, song position pointer. The system real messages include time messages such as timing clock, start, stop, continue, active sensing and the system reset. A system exclusive messages are defined by the manufacturer. Let us see the example of the MIDI message that is note on MIDI message. It consists of three fields. A status byte is followed by the two data bytes. In the free byte, the most significant bit is one that identify this as a status byte. This is a note on message. Since it is a channel message, it has a channel in its list significant 4 bits corresponding to the channel 1 to 16. So the note on message with the 0 0 0 0 indicate the channel number 1, with the 0 0 0 1 indicate a channel number 2 and so on. A note on message is always followed by the two data bytes. The data byte have most significant bit of 0. Here is an example of note which is played having the data byte address as 41x which is translated into 65 decibel. Similarly, the second data byte gives the velocity. Here is an example of the 5B that is 91 in decimal. The MIDI system interpret a note on message with the velocity 0 as a note off. Similarly, the alternative of the note off message uses the note velocity 0 for the note on message. Let me ask you one question. Let us say that a key is pressed and the second letter it is released. So how many bytes are required for playing a note for the second? You can pause this video, note out the answer in your notebook and you can resume the video to see the answer. Now let me answer this question. The answer is playing a note for one second requires a six byte. Here are some examples of the MIDI messages which have a note off message, note on message, polyphonic key press or after touch message, control message, program change, pitch bend change, channel mode message have channel which channel is selected in order to select in order to choose that we have the select channel mode, song select, timing clock and the system exclusive message. The M stands for 0 or 1 whereas N has a maximum value of f because of it is hex. Let us compare the MIDI data to the digital audio. Let us consider the example of 16-bit mono audio which is sampled at the rate of 44 kilohertz per second. See hence it will require total 88 kilobytes per second for the transmission whereas in case of the MIDI which is by playing the MIDI for a note one second it will require a six message. Digital audio recording of a sound tries to capture the sound exactly as it is occurred by the sampling of the sound pressure amplitude over the time. In case of the MIDI the records are symbolic messages. These messages make no sound unless and until it is interpreted by the synthesizer. In case of the MIDI recording means a MIDI data has been captured or stored not in the sense of the sound which is actually recorded. The word sample in case of the MIDI is different than that of the digital audio. In case of the MIDI sample is a small file which representing the single instance of the sound which is played by some instrument like a note played by the flute. So the MIDI data will require a very less space for the storage as compared to the digital data. So these are the references for the session. Thank you.