Signal Processing for Sound Synthesis: Computer-Generated Sounds and Music for All

D igital sound synthesis is celebrating its 50th birthday in 2007: It was first tested at the Bell Labs by Max Mathews and his colleagues in 1957, but it took quite some time before the technology was ready for the market. Digital music synthesizers were commercialized about 20 years later starting at the end of 1970s. In the mid 1980s, digital synthesizers became popular, when the musical instrument digital interface (MIDI) specification was released and incorporated in products. This enabled the playing of several synthesizers connected to each other or playing music synthesizers with computer control using so-called sequencing software. During the past five years, the MIDI music synthesizer has found its way to mobile phones. At the time of this writing there are about 2.5 billion mobile phones in the world. Many of them can play melodic (polyphonic) ring tones, which are usually generated from some sort of MIDI file (e.g., SP-MIDI) using wavetable synthesis. For this reason, almost everybody uses sound synthesis in their daily lives, although many may not know it. Sound synthesis is a field of technology in which signal processing plays a key role. The research focus has spread from music synthesis to various multimedia and entertainment applications, such as sound effects and background music for gaming, ring tones, and alarms, and interactive sound generation for virtual reality or other multimodal systems. In addition to musical tones, it is now practicable to devise algorithms for everyday sounds, for instance footsteps, hand clapping, or rolling wheels. Still, music synthesizers and related equipment, such as digital pianos, are popular, and they are continuously cultivated. Old sound synthesis technology does not disappear but is brought back to life with the help of new signal processing: take, for example, virtual analog synthesis, a methodology that emulates the oscillators and filters of analog synthesizers using digital signal processing. A