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Synthluver · Joined: Aug 18, 2009 Posts: 15 Location: Montreal

It's not a mystery from a programmer's standpoint, but it still can be very confusing.

The midi specification dates from computer stone ages where only 7 bits in an 8 bits byte were transmitted over modem lines (or send to specific instruments)

7 bits allow you a range of 0-127 (the standard values for midi CC's).

Most modern instruments use the full 8 bits per byte and midi protocols still packs them 7 bits in a byte, which means that all bytes must be repacked for transmitting over sysex. (but that's another story).

As far as using 8 bits per byte, there are two possibilities : unsigned bytes (these would range 0-255) and signed bytes (these would range -128 to 127, where the most significant bit is the sign, either 0 for positive or 1 for negative)

To make out a number from a unsigned byte to a signed byte (without using bitwise operators) it goes like this :

Suppose a number ranging from 0-255 (unsigned byte), the formula is

--- x = 200
--- if x > 127 then
--- x = x - 256
--- end if

Notes : it is up to the manufacturer to decide what kind of bytes they use, but for the most part signed bytes are used and the above is used programmatically in the firmware. CC's that may be using -128 to 127 as a range are shown as 0-255 to non programmer users.

Extended CC's (NRPN's) are coded with 14 bits per word (a word is two bytes) in a datatype called integer. Again, there are signed integers and unsigned integers

unsigned int : 0 to 65535

signed int : -32768 to 32767

x=40000
--- if x > 32767 then
--- x = x - 65536
--- end if

This is 16 bits mathematics, but because midi only uses 7 bits per byte, midi integers use 14 bits per byte, the most significant bit is the sign, the 15th bit is not used. Confusing? lollll that's not all... words are most often packed least significant byte first.

Ligumo · Posted: Fri Sep 30, 2011 11:30 pm Post subject:

I've been learning some Objective C/Cocoa/iOS programming - anyone tried to use that for this purpose?

Goof · Joined: Mar 02, 2011 Posts: 29 Location: Netherlands

Would be nice. Getting tired of manually copying and storing patches with the 3 digit led display and 2 up and down buttons...

rodhart · Joined: Jan 22, 2008 Posts: 18 Location: Brighton UK

Has anyone thought of an iPad app? I'm sure people would use it....