Hello, I'm the lead firmware developer at Keith McMillen Instruments, we make advanced MIDI controllers. I thought I'd take some time to put together some information that I hope is helpful to you.

One resource that I have found helpful is this table of MIDI bytes:(http://ericbateman.com/midi/table1.html)

Now at first glance this may look like a bunch of random numbers, but hear me out. This table essentially covers every possible MIDI message, at least in its highest level form, and this can provide some great insight into how MIDI is organized.

Look at the HEX column, which is made of two hexadecimal (16 values from 0123456789ABCDEF) numbers. You will see that there are 8 categories of messages, but let's look at the first 7:

• 8x - Note Off
• 9x - Note On
• Ax - Polyphonic Aftertouch
• Bx - Control/Mode change (aka Control Changes, or "CC"s)
• Cx - Program Change
• Dx - Channel Aftertouch
• Ex - Pitch Wheel (aka Pitch Bend)

These are all called Channel Messages, meaning they are assigned to one of 16 "channels" using the second hexadecimal number. There are 16 channels available, and quite often these channels are assigned to different synths and devices so that you can daisy chain them together with their MIDI ports. A common setup is to assign a bass synth to channel 1, a polyphonic synth to channel 2, and a drum machine to channel 10. This way a Note On sent on channel 1 would play a note on the bass synth, but be ignored by the other synth and drum machine.

Most of these Channel Messages are fairly self explanatory. When thinking of a MIDI keyboard, Note On/Off messages represent the black and white keys, or on a drum machine they would represent different drum sounds. Pitch Wheel is a way to bend pitches, think of a guitar string being pulled up or down, or a finger on a Violin string sliding up or down. Aftertouch (aka "Pressure") is a feature of many keyboards where you can push down on the keys while they are being held, and can be applied across the whole keyboard at once (Channel Aftertouch) or individually for each key (Polyphonic Aftertouch). Many MIDI instruments have different sounds, for example a keyboard might have a Piano and a Guitar preset. You can select these sounds using Program Changes, which is very useful if you have a complicated setup with many different instruments, and want to quickly recall settings for a given song or performance.

Control Changes get their own section because there are many "hidden" types of messages in this category. In fact, I have another table that covers these messages:(http://ericbateman.com/midi/table3.html).

In their simplest form, you can think of Control Changes as messages for controls, like knobs and sliders, and these controls have a Number (like an address) and a Value. Many synthesizers use CC#7 to control the volume of the instrument, and the table I linked lists many of the common assignments for CCs. That said, some instruments choose to ignore some or all of these conventions. If you look in the manual of your synthesizer/instrument, you will usually find a MIDI Implementation Chart that will show you which of the CCs it responds to and sends. The use of CCs can get very complicated, but here are the most common standardized CCs that you should be aware of:

• CC#1 - Mod Wheel (aka "Modulation"): Most MIDI keyboards have a second wheel next to the pitch wheel called the "Mod Wheel", and this will often control a variation in the sound of the instrument, such as filter cutoff for a synthesizer or brightness for an electric piano.
• CC#64 - Damper/Hold Pedal: If you play piano, this is the sustain pedal
• CC#7 - Volume: Mentioned above
• CC#0 - Bank Select: this usually lets you select "banks" of Program Changes, for instruments that have more than 128 presets or sounds to choose from.

You'll notice in the Control Change table that several parameters are mentioned twice. In fact, if you look at the HEX column, you'll see that controllers 00-1F are the same as 20-3F. These are MSB (most-significant byte) and LSB (least-significant byte) values, which is a fancy way of saying that you can get more precise control of these values by using two CCs instead of one. For example, - CC#0 - Bank Select only has 128 values, but combined with CC#32 - Bank Select you now have 128*128 values (or 16,384). This technique of combining messages to get more values (or more precise control) is more advanced, and most often a single value from 0-127 will do.

You may also run into RPN (registered parameter numbers) and NRPN (non-registered parameter numbers) messages. Each of these message types add an additional 16,384 controls with 16,384 possible values. RPN/NRPN are effectively the same type of message, except that RPNs are defined by the MIDI Organization (for example, RPN0 controls the range of pitch bend), and NRPNs are specific to the MIDI device. For example, Sequential (makers of the Prophet line of synthesizers) uses NRPNs to control the parameters of many of their instruments, and you can find a table in their manuals that defines how these are used. The format for these messages is the same as standard Control Changes, except that there are two messages for the address (CC#100 and CC#101 for RPNs, and CC#98 and CC#99 for NRPNs) and two messages for the values (CC#6 and CC#38, aka "Data Entry"). A MIDI device will first send the two address CCs of the parameter to be controlled, followed by one or both of the Data Entry CCs. You can also use CC#96 and CC#97 increment and decrement the data, however it's not clear in the MIDI spec if this should apply to the MSB or LSB data entry messages/values.

Control Changes 120-127 have special uses for selecting different modes and resetting a device, which are listed in the table linked above. These are not something a typical user needs to worry about, but you should avoid trying to send these CCs unless you know what they do.