MusicKit Introduction

The MusicKit defines a set of Objective C classes and informal protocols, C functions, and assorted constants and data types that are useful for creating music, sound, DSP and MIDI applications under NeXTSTEP, OpenStep, Windows9X, MacOS X and MacOS X-Server V1.2.

• The MusicKit provides a set of music representation classes―most notably MKNote, MKPart and MKScore, as well as MKEnvelope, MKWaveTable, MKTimbre, and MKPartials―that provide a flexible high-level structure for musical data. The MusicKit also provides a number of file formats for storing these structures. ScoreFile is a simple text-based scripting language that allows musical data to be represented in a convenient, human-readable form and supports simple programming structures. Alternatively, the MusicKit supports reading and writing musical data as Standard MIDI files, binary scorefiles (called “playscore files” for historical reasons) and NeXTSTEP archived objects. The MusicKit's representation system includes a number of enormously valuable features. The noteTag construct supports representation of phrase structure and makes it easy to create effects such as legato, which require continuity from one note to the next. The noteUpdate construct allows any aspect of a sounding note to be changed at any time.

• The MusicKit makes scheduling and sequencing extremely simple. A MusicKit "performance" consists of sending scheduled Objective-C messages and handling asynchronous events such as incoming MIDI and NeXTSTEP events. The MKConductor class is in charge of dispatching all messages and managing the notion of time. A MKConductor may have a tempo, a time map, or may be set to synchronize to MIDI time code. Since all time control is managed in the MKConductor itself, the difference between these time representations is completely transparent.

  Another aspect of the MusicKit performance is a dynamically patchable MKNote-handling network consisting of three classes, MKPerformers, MKNoteFilters and MKInstruments. MKPerformer subclasses are MKNote-generators, that sequence over NSArrays of MKNotes or create MKNotes on the fly. They contain outputs that may be connected to MKNoteFilters or MKInstruments. MKInstrument subclasses realize MKNotes in some manner, for example by playing them on the DSP or via MIDI, and contain inputs that may be connected to MKNoteFilters or MKPerformers. MKNoteFilters are intermediate processors that contain both inputs and outputs. This scheme makes it easy to create a performance scheme for nearly any application. The inputs and outputs are represented as MKNoteSenders and MKNoteReceivers, respectively.

  The MusicKit's performance apparatus is based on the notion that messages execute quickly. Thus, time stays constant during the execution of a scheduled or event-triggered message. This has the advantage of allowing a large number of DSP updates to happen at the exact same time. The DSP and MIDI driver support time-ordered queues of events, thus allowing the application some latitude in computing these updates, while still providing an instantaneous execution of the updates themselves.

• The MusicKit has extensive support for sound processing and synthesis on multiple DSP chips. Instances of the MKOrchestra class correspond to DSP chips and manage dynamic memory and processing time allocation. Full dynamic loading during a performance is supported. Synthesis insruments are represented as MKSynthPatch subclasses. The MusicKit SynthPatch library is an auxiliary library that consists solely of MKSynthPatch subclasses, each of which implements a generic synthesis technique. For developers or composers who want to create their own synthesis or processing configuration, the MKUnitGenerator class is provided. Each MKUnitGenerator subclass corresponds to a DSP module such as a filter, oscillator, or delay unit. By interconnecting these MKUnitGenerators using "patchpoints", a huge variety of synthesis and processing techniques may be implemented. The MusicKit UnitGenerator library is an auxilliary library that consists solely of MKUnitGenerator subclasses. Finally, adventurous developers may write their own DSP unit generators in MC56001 assembly language (using an extensive set of macros to simplify the process) and use the tool dspwrap to automatically generate Objective-C MKUnitGenerator subclasses.

  Currently, only the MC56001 is supported. The ArielQP and ArielQPSat classes support the Ariel QuintProcessor hardware, available for the NeXTcube.