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Midi workstation basics


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  • 1. The MIDI Workstation The MIDI (Musical Instrument Digital Interface) protocol was established in 1983. The brainchild of Dave Smith (Sequential Circuits), Ikutaro Kakehashi (Roland), and Tom Oberheim, MIDI was a pioneering cooperative effort, uniting internationally competitive companies in the quest to create a global platform to assist in the commercialization of their individual products. However, the unification of vastly differing technologies necessitated compromise, and resulted in several MIDI limitations, primarily a low data transfer rate (bandwidth protocol), unidirectional communication between devices, and lack of control over subtle nuances of sound.
  • 2. The MIDI Workstation The establishment of MIDI for keyboard interface prevented (or made extremely difficult) non-keyboard related gestures. Regardless, MIDI became an important platform for developments in interactive performance systems; proprietary hardware devices could now be interconnected, facilitating the design of robust, custommade portable interactive environments. Though the low data transfer rate limited the representation of complex musical structures, it nevertheless permitted real-time processing of musical information.
  • 3. MIDI (Musical Instrument Digital Interface) consists of both a simple hardware interface, and a more elaborate transmission protocol. Hardware features MIDI is an asynchronous serial interface (meaning messages are sent out one after the other). The baud rate (transmission speed) is 31.25 Kbaud (+/- 1%) or 31,250 bits per second. The MIDI circuit is current loop, 5 mA. (m = Milli (10-3) & mA = Milliampere). Logic 0 = current ON. One output drives one (and only one) input., The MIDI specs. recommend the use of an optoisolator to avoid grounding problems. An optoisolator is a sealed device which contain both an LED and a photosensor (see the diagram that follows) . These require less than 5 mA to turn on. Rise and fall time for the optoisolator should be less than 2 microseconds.
  • 4. Schematic of a MIDI Interface
  • 5. MIDI connectors and cables The standard connector is 5 pin DIN. Separate ports and cables are used for input and output. 15 metres is the recommended maximum cable length. Cables are shielded twisted pair,. Pins 4 and 5 form a shielded twisted pair, with the shield connecting pin 2 at both ends. Pins 1 and 3 are not used. A device may also be equipped with a MIDI THRU jack which is used to pass the MIDI IN signal to another device. Time delays caused by the response time of the opto-isolator may result in timing errors , therefore there is a limit to the number of devices that can be daisychained.
  • 6. Other numbering systems Decimal: expresses quantities in powers of 10 1999= 1(103) + 9(102) + 9(101) + 9(100) Binary: expresses quantities in powers of 2 144 = 10010000 144 = 1(27) + 0(26) + 0(25) + 1(24) + 0(23) + 0(22) + 0(21) + 0(20) 144 = 128 + 0 + 0 + 16 + 0 + 0 + 0 + 0
  • 7. Other numbering systems (cont.) Hexadecimal: expresses quantities in powers of 16 using the symbols 1,2,3,4,5,6,7,8,9,A,B,C,D,E,F. Examples: 60 = 3Ch or 60 = 3(161) + 12 10010000 = 144 = 90h 00111100 = 60 = 3Ch 01000000 = 64 = 40h
  • 8. Converting from decimal to binary Convert the value 44 from decimal to binary 32 16 8 4 2 1 1 0 1 1 0 0 Let D= the number we wish to convert from decimal to binary (44) Find P, such that 2^P is the largest power of two smaller than D (32) Repeat until P<0 So…….If 2^P<=D then put 1 into column P subtract 2^P from D Otherwise put 0 into column P Continue until complete! Try a few out and use this conversion tool to check your answers