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A By MICHAEL HAWKINS LTHOUGH MIDI HAS BEEN around for nearly 10 years, few people really understand it and certainly most don't know its full capabilities or its inadequacies. I'm going talk about the grass roots of MIDI, particularly with a view to eventually building your own MIDI gear. But first let's get a misunderstanding out of the way concerning the use of the term "midi". Unfortunately, Japanese manufacturers have used the term midi to describe the smaller rack mounting hifi systems which have proliferated over the last few years. They are called midi because they are mid-sized. Midi hifi gear has nothing to do with the MIDI equipment used by musicians. Now having got that out of the way, let's have a quick look at where we were 10 years ago. Before MIDI Up until about 1980, music synthesisers were based around analog technology; ie, the way they made noises was by using a voltage controlled oscillator (VCO). The oscillator would feed into a voltage controlled amplifier (VCA) and then into a voltage controlled filter (VCF). There would be a few envelope generators that provided the control voltages for the VCA and VCF and the keyboard would provide the control voltage for the oscillator. These instruments were generally mono; ie, you could only hit one note at a time. They had a few sockets on the back called CV and CV gate (or something similar). CV stands for control voltage and it allowed you to control the keyboard from another keyboard or sequencer. The control voltage was The Musical Instrument Digital Interface The purpose of this article is to introduce and explain the technical aspects of MIDI which stands for Musical Instrument Digital Interface. This is used by virtually everyr recording outfit, from million dollar operations right down to the humble busker. 16 SILICON CHIP D KEYBOAI\D SYNTHESIZER 00 - ~_J-"J~:: 1111~1rn11~1m~1i1~1~~1I1i L__I PERSON~.M~MPUTER ~THWWJGH-l~i~ OUT MIDI INTERFACE KEYBOARDLESS SYNTHESIZER MODULE ORUM 1'"1~"" Ml1911 c::::::J HHB O I rnmm c::::::J 'AUDIO I AUOIO I MIDI OUT I THROUGH ,--- -- - -- - - -- - - - - _ _ _ . OUT .---- - - ---- - ---------- ---- -EFFECTS OUT __._ t MIXING OESK 0 0 0 0 0 0 0 0 0 'o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lo 0 0 0 0 0 0 0 0 0 0 0 L __._ _ __ _ __ t I 0 0 0 0 MIDI r--- -~TH=R= OU~G--;HI O tA~~IO C::=J O O _, AUOIO OUT a c:, MIOI ..,1;,;.N_ _ _ _....1 EFFECTS UNIT ~B 0 0 0 0 0 0 0 0 0 0 fri+tlll t t 0 0 0 90 o, MULTITRACK TAPE RECORDER 0 0 0 0 0 0 0 O 0 I I I I I I I 0 Fig.1: this diagram shows just some of the equipment which can be hooked together and synchronised via the MIDI bus. Not shown here are MID] samplers and tone generators. 1-volt per octave. The range was 10 volts so you could play notes across 10octaves. For the technology at the time, this was quite good and many people used this sort of gear with fantastic results. However, to build up a large number of notes with a few different instrument sounds required an awesome array of equipment and you needed to understand all the technology fairly well. Just prior to 1980 though, synthesisers started appearing with polyphonic capability; ie , you could play more than one note at a time (usually eight). With miniaturisation, all the VCOs, VCAs and VCFs could be packed into smaller spaces, allowing one instrument to contain many such circuits. The only problem here was that the CV gate system only allowed you to control one note externally. It became apparent that some sort of interface was going to be required to allow lots of notes to be controlled at once. A few attempts were made by individual manufacturers to introduce different interfaces but none of them took off, mainly because they did not address all the problems of reproducing music. Some of those problems were: (1) you should be able to change a synthesiser's sound remotely; and (2) you should be able to synchronise drum machines and sequencers and tape machines to each other. Up until 1983, the industry generally remained confused. In 1983, the International MIDI Association (originally made up of a conglomerate of representatives from cooperating instrument manufacturers) released the MIDI specification 1.0. i This non-profit organisation had defined a standard for the interfacing of electronic music devices based on digital communication techniques. Due to the fact that most devices had microprocessors in them already, it was reasonably easy to integrate MIDI into machines and so , within a year, all major manufacturers had begun supporting MIDI. Within another • i:· ,,!inl!'l'SIOII llll ( A small MIDI interface card for the expansion socket of any PC/XT/AT system and the right software allow musicians to do things that were unheard of just a few years ago. The Miracle keyboard which we reviewed in the December 1991 can be part of a comprehensive MIDI system linked to your computer. AUGUST 1992 17 One of the most rewarding pieces of MIDI equipment a musician can use is the sampler. The Akai SHOO is a popular instrument which gives CD quality sound with 44.lkHz 16-bit sampling. Sound waveforms can be sampled, viewed on the screen and modified at will. The unit can have up to 32 megabytes of memory and extensive sound libraries are available. It even has a SCSI port for an external hard disc drive. year, virtually all other interfaces had been dropped. One significant feature of MIDI was that it wasn't restricted to just turning notes on and off. It has various modes and levels of control, thus allowing virtually any type of music gear to be attached. Let's digress and have a quick look at what can be attached and done with the technology around today. A typical home studio These days, you can have your own home studio, with every piece of gear connected via MIDI - including your personal computer. You might have a keyboard, a sound module, a PC, a few effects units, a drum machine, a mixer and a multi-track tape recorder. Loaded onto your PC will be a sequencer package that will allow you to control every piece of gear to varying levels. For example, you would have corn- 18 SILICON CHIP plete control of the keyboard, the sound module, the effects units, the drum machine, and partial control of the mixer depending on how much MIDI is implemented into it. And you could probably synchronise the tape recorder to the drum machine and the PC. Therefore, you could compose and play your music, recording one instrument at a time on the PC. While the PC replays your first instrument, you record a second one, and this process is repeated until you have all the instruments recorded. You then set up the effects units with just the right reverb , echo and chorus that you want and record those settings on the PC. Finally, you can set up the mixer with just the right EQ (equalisation) and volume levels before recording the whole thing on the tape recorder, which in future will be able to synchronise the PC to itself so that you can change, add or delete whatever material you wish. Furthermore, all the settings, mixing levels, echo, chorus, music , etc will be recorded on the PC as a file that can be saved to disc. This can be sent to someone else via modem or the music score printed on a standard printer. Let's briefly define the purpose of each device I have just mentioned in the last paragraph, along with a synopsis of the kind of controls that each unit is likely to have. Keyboard: has a piano type keyboard, generates sounds, has many controls over the sounds produced, pitch bend, transpose. Sound Module: same functions as a keyboard but does not have a piano keyboard. It uses MIDI to allow other keyboards to make it produce sounds. Has the same control over the sounds produced, either through a panel of switches etc, or via MIDI. Effects Unit: a device which takes the audio outputs from other sound generating equipment and alters the sound using delay or filtering. Usually, the effects produced will be reverb (makes the sound sound like a concert hall) or echo. Other effects are phasing, flangeing, chorus (sounds like more than one instrument), or even harmonising. Has control over Today's MIDI keyboards offer a wealth of facilities for the innovative musician. This 61-note model DX711 D/FD from Yamaha has 64 voice memories, 32 performance memories, liquid crystal and LED alphanumeric displays and a 720Kb floppy disc drive for data storage. A. : ll1lf!!f,If,,11 ' I l\,,\\,\\,,\\\ ttU>.lfi,11' - - - - ------ ---- --~- 1 .· =;.,.,...,,.,,·_,· __ 1_-···~...-..i-·•----,..,....._·_1_, . - ¥• . • "--• This Kawai MIDI keyboard is shown together with a MIDI interface card and a number of software packages including the Musicator, which runs on 286 machines or higher. It turns the PC into a 16-track sequencer but also will record in real time from a MIDI keyboard and transcribe it into sheet form. delay times, sweep times and many others. Drum Machine: a unit that produces percussive sounds. Usually can be programmed to repeat drum patterns. Has controls over virtually every aspect of percussive sound generation. Can be started and stopped manually or via MIDI. Can also be synchronised to other equipment via MIDI. Mixer: takes the audio outputs from any device (ie, instruments, microphones, effects units, etc) and combines them into a few outputs suitable for recording on tape. Has control of EQ (tone), volume and level of effects. Some recent mixers are able to be controlled via MIDI. Sequencer: either a dedicated device or part of a personal computer that allows a music score to be recorded as digital codes (not as actual audio sounds) and be altered, replayed and stored digitally. Has control over virtually all aspects of music composition, depending on the type of sequencer. Information going into or out of a sequencer will usually be MIDI. Can be synchronised to other equipment via MIDI. not unlike the modem port found on PCs (although it's a current loop). Each MIDI device will normally have a MIDI In port and a MIDI Out port and maybe a MIDI Thru port. These are 5-pin DIN sockets which only use two pins. Whatever is received at a MIDI In port is always immediately repeated at a MIDI Thru port. So Thru ports are useful for cascading devices with only one control device. • ,._...,,,___r---1- - ·.- f The MIDI Out port simply transmits MIDI information that originates from that particular piece of gear. However, most devices have a facility called "Soft Thru" which allows you to repeat at the MIDI Out port whatever is received at the MIDI In port and transmit all the information originating from the device as well. There are three basic types of information transmitted down MIDI. Let's have a look at each group. Channel voice messages One main area of confusion with MIDI is exactly how each instrument is "spoken to" via MIDI. Just how does MIDI at the lowest level So what actually is MIDI from the hardware side of things and from the lowest level of software? MIDI is an asynchronous (serial) 5mA current loop interface, running at 31,250 bits per second. It transmits eight bits with one start bit and one stop bit. Basically it's a fast serial link One of the most common MIDI instruments you are likely to see in any musical combo is a drum machine such as this Akai MPC60 II which is an integrated sequencer and drum sampler. · AUGUST 1992 19 Want more instruments in your combo? The Roland RA90 Realime Arranger offers one way to get them. It is a MIDI peripheral unit which adds backup instruments as well as providing the facilities of a digital drum machine. one instrument know to play a note while all other devices remain quiet? Quite simply, each device attached to MIDI is assigned a channel from 1 to 16. Every channel voice message carries along with it a channel number, 1-16 (but actually sent as 0-F hex). Channel voice messages can be divided into two sets of commands. Voice messages turn notes on or off and the mode messages alter parameters on the designated instrument. For example, mode messages change an instrument's sound (violin to distorted guitar) and pitch bend (for those sliding guitar notes), and alter the touch sensitivity of an instrument (the difference between when your cat runs up your piano or your pet elephant). Channel voice messages could be argued as being the most important commands sent through MIDI simply because they are the commands that actually make instruments play music. System messages System messages are acted upon by all attached equipment; that is, system messages don't have a channel number sent with them. And you guessed it, they can be divided into a few categories: Common, Exclusive and Real-Time. There are only four Common messages. One sets the position of a song before it starts to play. Song select tells all attached devices what song to use. Tune request is rarely ever used (I have never seen it) and instructs Analog Synthesisers to tune themselves. The last command is the EOX ("End of System Exclusive") which leads us to System Exclusive Messages. Exclusive messages are manufacturer dependent commands. Each exclusive message starts with an organisation identification number. Then follows a limitless string of data which must be terminated by the EOX command. System exclusive data ·can be used for anything the manufacturer wishes. Often, it's used to transmit entire blocks of data used by an instrument to create new sounds to replace or alter the original ones programmed in. It can also be used to control manufacturer specific capabilities. Real-time messages are used to synchronise drum machines, sequencers and personal computers together so that they all play their pre-recorded YAMAHXS MIDI WIND INSTRUMENT MIDI keyboards and stringed instruments are fairly commonplace but have you heard of a MIDI wind instrument? The Yamaha WX7 Wind MIDI controller allows wind instrument players to directly play the most advanced synthesisers and tone generators available. There are sensors for breath pressure and lip pressure to provide the control facilities. · 20 SILICON CHIP tunes, beats, etc, in time. There are start, stop and continue commands. These three commands allow all instruments to be started or stopped at exactly the same moment and continue lets you continue from where you last stopped. Finally, there is the time clock command which is sent down MIDI at the rate of 24 clocks per quarter note. This is the command that actually keeps instruments in time with each other. Only one instrument at a time should send time codes, otherwise there will be time codes going everywhere and resulting instrument confusion en masse. The start, stop and continue commands, however, can be sent by any machine. There is one more real-time message called System Reset. It is rarely used (my peepers haven't ever seen it used) and should preferably not be used unless something has gone haywire. Its purpose is to reset every attached machine back to the state of first being turned on. Channel Mode Messages MIDI has four modes of operation available that are dependent on two variables, OMNI on/off and POLY on/ off. Generally, channel mode messages are sent when MIDI is first fired up and sent by the master sequencer or PC. There are two other uses for channel mode messages. One is an All Notes Off command, which is used to make sure all notes are turned off in an instrument. The other is to allow local control of an instrument to be turned on and off. Local control can be turned off so that the instrument only responds to MIDI note events and does not play notes if keys are hit at the particular instrument. But, when a key is hit, its MIDI note on and Note Off command will still be sent down MIDI, allowing other devices to respond or record the event. Well, that's probably enough technical jargon in one article but it should be enough to give the concept of MIDI - the musical instrument digital interface. To sum up, it is an 8-bit serial data system running at 31,250 bits per second. It is similar in some aspects to the serial data transfer system used in remote control of model cars and aeroplanes. The difference is that while a remote control system will have different channels devoted to SILICON CHIP AUSTRALIA'S BRIGHTEST ELECTRONICS MAGAZINE Three good reasons why you should subscribe to SILICON CHIP 1. You get a 12.5% discount on the newsstand cover price. Last year, we had to increase the cover price of the magazine because of rising costs but we have held the subscription to the old price so you get the benefit. Understanding The World Of CB Radl<> , ' • _. f T - 1 S!RVICINO-VMAOE AAl)JO •·• (.::(')jVffl'IJTEJt$ -AMAtWII RA,DtQ ., .• PllO,ja;T,s TO 1UJ1W 2. You'll never miss an issue. Sometimes it can be very hard to find SILICON CHIP in the newsagents because it sells out early or gets buried under other magazines. By taking out a subscription you don't have to search for it - it arrives in your letter box in mint condition. We wrap it in tough plastic to make sure of that. 3• Get a discount on the binder too. You '11 want to store and protect your issues of SILICON CHIP so when you take out a subscription you get a further discount on the binder. By taking out a 2-year subscription and buying two binders at the same time, you get even bigger savings. And we despatch the binder(s) with your first issue so you have it right from the start. Interested in these savings and benefits? Just fill in the coupon on page 92 and send it with your remittance. Or telephone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. You'll be glad you did. Why not do it today? I hope to see you as a supporter soon. Leo Simpson, Publisher control of throttle, flaps and so on, the MIDI system has different channels devoted to different instruments. In a few month's time, I 'hope to present a simple way for you to get involved with MIDI music. That's the best way to understand the system. See you then. SC AUGUST 1992 21