Chapter 12The Principles of Computer Music

Contents•Digital Audio Processing•Noise Reduction•Audio Compression•Digital Rights Management (DRM)

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• A working approach to music development on computers encompasses the programming of musical parameters using a central processor, the storage and retrieval of said parameters, audio synthesis of the parameters, editing, and the playback or synthesis of completed works represented by such parameters.

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• In a digital music system, quantities representing the frequency, amplitude, timbre, duration, and envelope of a sound are expressed as numbers. Computers are designed to interpret and manipulate ordinary decimal numbers that are stored as binary numbers using only 1s and 0s.

• Computers are operated by providing a list of procedures (algorithms) that can be organized as a sequence of instructions using binary code.

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• Sound can be generated from a computer by either synthesizing original tones from scratch or by converting analog audio signals into a digital signal that can be further manipulated.

• Techniques for generating sounds using a computer include direct digital synthesis, complete sampling, note sampling, and wavetable synthesis.

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• Three major kinds of wavetable synthesis techniques are additive, subtractive, and modulation synthesis.

• The Nyquist sampling theorem states that a time-sampled waveform can only be adequately represented if the sampling frequency is at least twice that of the highest desired frequency being sampled.

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• Although noise reduction systems as once implemented with analog music production systems are not required for digital music production, the DSP function of dithering is used to avoid noise introduced during the sampling process.

• Data compression algorithms that retain the full spectral fidelity of the original audio file are termed lossless and contrast with so-called lossy data compression algorithms that cannot reconstruct the compressed signal to its original specifications.

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