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What are MIDI Basics?
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What is MIDI anyway?  First, MIDI is an acronym for Musical Instrument Digital Interface.   It is a standard or an agreement among the various musical instrument manufacturers that we will all use the same kind of connections and electrical signals so that any two musical instruments can be connected together and work. CONNECTIONS: MIDI connections are all made with “5 pin DIN cables” that plug into “5 pin din jacks” on the musical instruments.  Only two wires are used in these cables to carry the information from one instrument to another.  A MIDI Out jack is used by an instrument to send information to another.  A MIDI In jack is used by an instrument to receive information from another.   
SIGNALS: The electrical signals of MIDI are digital, not analog.  This ensures that the communications will be exact.  The expression “close enough for rock-and-roll” doesn’t apply here.  If you want to hear a snare drum, but some of the time hear a bass drum instead, because they are close to each other in the note table, you’d get upset. Digital gives you exactly what you asked for. The signals are serial, not parallel.  This means you don’t need a complicated or expensive cable to make the connection.  One pair of wires in the cable will do. The signals are opto-coupled.  Current flowing through the MIDI cable turns on a tiny light inside a chip inside the receiving instrument which ends up producing the electrical signal that the receiving instrument uses.  Wow! Cool, huh!?  That means that there is no ground connection between the MIDI-connected instruments.  This eliminates 60 cycle hum from ground loops between these instruments.
CONCEPTS & COMMANDS: The main Concepts you need to understand are:  MIDI Channels, MIDI Notes and MIDI Velocity.   The main Commands you need to understand are:  MIDI Note On, MIDI Note Off, MIDI Program Change, and System Exclusive.
CONCEPTS: If we use a telephone line analogy, MIDI Channels are like phone numbers.  Sound Sources are like homes.  MIDI Notes are like the individual people in the individual homes that has that phone number.   MIDI Velocity is like the information you tell the person you are talking to. A separate MIDI Channel is usually assigned to each Sound Source you are using (like a phone number per home).   There are 16 different MIDI Channels available (there’s a lot more phone numbers - you probably have more friends than sounds sources!).  To make MIDI work for you, you need the Channel your sound source is set to receive on match the Channel your trapKAT is sending on.  It’s that simple! On the trapKAT you can have every Pad send on different Channels if you want - that is an advanced use - if you have more than 1 sound source.  Generally, you will set all Pads of your trapKAT to send on the same Channel as your sound source is set to receive on.  Most commonly used Channel for drum sounds is Channel 10.
• So, to get your sound source to respond at all, you first need to match up the Channel you are sending on to the Channel your sound is receiving on. Each Sound or Pitch within each Sound Source is accessed by the MIDI Note Number that is sent (just like asking for the person by name when you reach the correct home).   
•  So, to get the correct sound to play (in the sound source you are controlling) when you hit a Pad, you match the MIDI Note number on your trapKAT Pad to the Note number that plays that sound in your sound source. The Velocity that is sent tells the Sound Source something about the dynamics of the Sound - usually how loud to play the Sound.  A Note with a low velocity value will play softly.  A Note with a high velocity value will play loudly.
• After you train your trapKAT to respond to your playing dynamic range (what soft and hard hits are to you), the trapKAT will send out the appropriate velocity based on your playing dynamics.
COMMANDS: A MIDI Note On Command tells a specific Sound Source to play a specific Sound at a specific volume.  It turns a Sound on.   It contains which Channel (which sound source) to play, which Note (sound) to play, and which Velocity (loudness) to play. A MIDI Note Off Command tells a specific Sound Source to stop playing a specific Sound .  It turns a Sound off. It contains which Channel (which sound source) and which Note (sound) to shut off. (Most drum machines actually ignore Note Off commands.) A MIDI Program Change Command is used to tell another instrument to use a specific Kit or patch of sounds or settings.   A Program Change sent to a drum machine will generally call up a different Kit of drumsounds.  A Program Change to a synth would call up different sounds (flute, piano, xylophone, etc.).  A Program Change Command to a Lighting Effects unit would call up a different lighting setup. A MIDI System Exclusive Command is something specific to a particular instrument.  It is typically used to do Data Dumps.   A Data Dump is when an instrument sends its settings out MIDI in a big group so that they can be saved on some storage device (like a computer or a MIDI disk drive).  Then the Data Dump can be sent back into the instrument later on to retrieve those settings again. Data Dumps are used as a back-up against the accidental loss of your settings or Kits.
1.  Match the Channel your trapKAT is sending on with the Channel your sound source is set to receive on.
2.  Match the Note numbers on your trapKAT Pads to the sounds you want your sound source to play.
3.  Use Program Changes to select other groups of drum sounds or other pitched sounds.
See p.31-34 in the trapKAT manual.
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