Real-time music synthesis in Java using the metronome garbage collector

Abstract

Automatic memory management via garbage collection is the key to the safety, portability, and high productivity of modern programming languages like Java. However, until now no truly real-time garbage collector has existed for Java. As a result, the extreme real-time requirements of interactive music synthesis and processing have made it impossible to build such systems in Java. We have developed a hard real-time garbage collector, called Metronome, around which IBM has built a production real-time Java virtual machine running on a realtime variant of Redhat Enterprise Linux. In this paper we demonstrate the real-time capabilities of our virtual machine with a MIDI music synthesizer that we built entirely in standard Java using the full object-oriented feaures of the language. We show that even with the addition of another thread allocating 8 MB/second of data, our garbage collector is able to sustain error-free 44 KHz music synthesis down to buffer sizes of 1ms, achieving keyboard-to-speaker latencies of 5.0±0.75ms, comparable to a Kurzweil K2000R synthesizer (3.9±1ms) and suitable for high-fidelity interactive performance.