Because of its unique features MIDI is rarely suitable for direct connection into a computer. With most computers a MIDI Interface is necessary — with the Apple Macintosh it is essential.
The simplest type of interface is almost ‘passive’. It conveys information at MIDI rate, in both directions, between the MIDI connections and the serial ports of the Mac. It provides MIDI inputs and outputs — the latter often duplicated — for both printer and modem ports. The interface generates a reference signal (usually 500 kHz or 1 MHz) which the Mac then divides down to generate the MIDI bit rate.
To use software intended for editing sounds within a synthesiser or for sound manipulation it is essential to connect both the inputs and outputs of the appropriate device to the interface.
The Opcode Studio 5 is a pioneering example of an intelligent interface — it conveys data for 15 MIDI inputs and outputs in the time normally taken for a single MIDI byte. MIDI data is ‘wrapped’ within extra codes — identifying the particular input or output — which are then made ‘invisible’ using software inside the Studio 5 and the Macintosh.
„ Interfaces such as these cannot work without the appropriate Mac software.
 
 
 
MIDI Software on the Mac
wwwwwwwwwwwww
MIDI driver software is responsible for handling any data passing through the Mac ports. In Standard MIDI this is contained within each program — unfortunately the action of switching between different MIDI programs will give unpredictable results (since each program will operate on the serial ports independently of any other applications).
An alternative driver called the Apple Midi Manager overcomes this by keeping control of MIDI at all times, whatever program is active. An accompanying utility called PatchBay allows the user to create MIDI paths between Mac ports and applications — just by drawing lines.
But Midi Manager has a limitation — it only allows one MIDI input and output to operate through each port of the Macintosh. Since multi-timbral instruments — which can play up to 16 sounds simultaneously — can occupy the entire capacity of a MIDI circuit this is quite inadequate.
The Open Midi System (originally called the Opcode Midi System) neatly overcomes this problem and allows sequencer, editor and Studio 5 software to operate as a unified package. To do this it replaces the Midi Manager by its own ‘substitute’, allowing the use of PatchBay and other Midi Manager applications, whilst ‘OMS applications’ operate invisibly ‘behind’ PatchBay.
 
 
 
In the example shown above the system has been set up to receive timecode at 25 frames per second. Filter Timecode has been set on in order to segregate the timecode from other data.
An additional utility called SquidCakes, used in conjunction with PatchBay, enables the user to monitor the actual MIDI data which may be flowing into or out of any application which employs MIDI Manager.
