Labels:text | screenshot | font OCR: AM/FM (1) 300000000000000 Written for AM/FM by Kevan R. Craft. 3 MUSICAL INFORMATION TRANSMITTED Via MIDI MIDI Channel and Mode 1. MIDI is able to transmit a variety of information from a master instrument. Either on part, or multiple parts can be transmitted, for example via a sequencer system. For this purpose, MIDI includes 16 "channels". All the different types of MIDI conversation can be sent via these 16 channels separately. So, with one MIDI cable, 16 parts can be played at the same time. The concept of MIDI channels is similar to that of T.V. broadcasting in a sense. many T.V. stations are transmitting their respective programs at the same time. This means that your T.V. antenna must be receiving all these channels at once. however, since all the stations are transmitting on different channels, you simply need to select the channel you wish to watch. MIDI channels behave the same way. A MIDI master instrument or computer sequencer is just like a T.V. broadcasting station. A MIDI slave instrument is like your T.V. receiver, although rather than transmitting through the air, MIDI is transmitted via cables (ie 5 pin DIN). The MIDI master instrument can decide which instrument to transmit, rather like choosing which T.V. station it wants to be. On the other hand, the slave instrument can behave like the T.V. set and choose which MIDI channel it wants to "hear". Even if information is received on all 16 channels, the slave will only "hear" the chosen channel, just like the T.V. set. For example, if the instruments are set up as synth 1 outputting to synth 2, ie MIDI OUT to MIDI IN and synth 2 outputting to synth 3, ie MIDI THRU to MIDI IN, synth 2 only receives the information on channel 1 through the MIDI cable. Synth 2 only receives information on channel 2 through the MID the MIDI cable. So that if the MASTER synth is sending data on channel 1, 1, only synth 1 1 will respond. Similarly, if the MASTER synth is transmitting data on channel 2, only synth 2 will respond. Even though synth 1 is obviously receiving the information, it cannot respond because it is switched to a different channel. In other words, for this system to work correctly, YOU MUST CAREFULLY SELECT MIDI CHANNELS. 2. Modes As we mentioned earlier, it is neccessary to use the same MIDI channel if a master and a slave are to play in unison, but there is another way to make the slave receive the information. This mode is called "OMNI ON", and it forces the slave to respond to all 16 channels at once. Modes Cont/ In a simple set-up of one MASTER and one SLAVE, this becomes very useful, because the slave doesn't care which channel the master is using, it will "hear" them all. However, when using a sequencer playing on a variety of different channels, it is impossible to separate the information. So then the SLAVE must be in the OMNI OFF mode, so that it will only receive information on the chosen channel. There are also "POLY" and "MONO" modes in MIDI, which decide whether the information is to be sent as "monophonic" information (one note), or "polyphonoc" information (more than one note). Keyboard instruments such as pianos and synths usually use the POLY mode. MONO mode is mainly used for MIDI guitar controllers like the Roland GR50 guitar synthesizer. In this mode, the information belonging to each guitar string is sent on separate channels, dividing the sound source into 6 monophonic synths. Then a basic MIDI channel is set, and the next 5 channels are used for the other strings. To choose whether to use POLY, MONO, OMNI, etc, MIDI includes a MODE selector, with 4 possibilities, MODE 1-4. MODE 1: OMNI ON, POLY Receives the information on all channels Polyphonic. MODE 2: OMNI ON, MONO Receives the information on all channels but will only play one note at a time MODE 3: OMNI OFF, POLY Receives only on the chosen MIDI channel Polyphonic, useful with sequencers. MODE 4: OMNI OFF, MONO Receives on specific MIDI Channel(s), will only play one note per channel. Useful with guitar controllers. (2) Main Contents of MIDI Information MIDI contains many kinds of information, that it can use to transmit performance details from the master to the slaves. Such things as when each note was played or released (note on and note off), damper pedal on and off, etc. Also, the information is divided into "channel messages" and "system messages". 1 Channel Messages These messages are sent via the individual MIDI channels to specific instruments in the system, and therefore only effect those instruments receiving that channel. Channel Messages include note on/off, damper pedal on/off, pitch bend on/off, etc.. These Channel messages are further divided into 2 categories, "Voice messages" and "Mode Messages". a. Voice Messages - Note Information - Note Information is the most basic, it simply says which key was pressed, when it was pressed, and when it was released. - Program Changes - A Program Change is used to cause the slave to change its sound. Synths, electronic pianos, and sampling machines have memories full of many sounds. With these Program Changes the musician can choose which sound to use. It is also possible to switch the memories of MIDI effects and devices. - Control Changes A Control Change can add subtle nuance to a performance, things like portamento. (ie, vibrato and tremolo, hold (damper) pedal, soft pedal, and These messages are not used in all MIDI instruments. An electric piano will send and receive pedal damper information, but it certainly does not require portamento. So even of the master instrument has portamento, the piano will not respond to that information. To find out which controllers a specific instrument will respond to, refer to the "MIDI Implementation Chart" at the back of the owners manual for that instrument. - After-Touch Synths and samplers can control vibrato, brilliance, volume, etc, by simply pressing the key harder after initially playing it. This is called "After-Touch", and can be used to transmit the same effects via MIDI. Of course, the slave instrument must then decide how to use the After-Touch information it receieves. - Pitch Bend - If the master has a pitch bender, the information may be sent via MIDI. Once again, the slave will decide if it wants pitch bend, and even how much it wants. b. Mode Messages As mentioned earlier, MIDI has 4 MODES, and MODE messages are used to switch the MODE of a slave. Some synths or electronic pianos are in MODE 1 (OMNI ON, POLY) whenever they are switched on, so you will need to switch them to MODE 3 (OMNI OFF, POLY) for use with a sequencer. Because of this, some sequencers will automatically send a mode message to turn the slaves to MODE 3. Turning the slaves power on first, followed by the power of the master, will often acheieve the same result. NOTE: Make it a habit to always turn the master on last. 2. System Messages System Messages can be sent no matter how the MIDI channels of the slave or the master are set, since they are used to control the whole MIDI system, that is, every instrument connected to the MIDI cables. For example, they can be used to synchronize a sequencer and drum machine, so that they play exactly in time together, or to start and stop the performance, or simply to avoid MIDI system problems. Also, there are messages called "System Exclusive Messages", which are messages that are exclusive to a particular manufacturer. So that each manufacturer has an "ID Number" which their instruments will recgnize. Any system exclusive data received with the wrong ID Number will be ignored by that manufacturers machines. With Exclusive Messages it is possible to transmit sound between synths, or to change the parameters of a synth via a synth software program. AM/FM
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