Wavetable synthesis

Wavetable synthesis' is a digital technique used to create periodic waveforms.

Development

In 1958 Max Mathews used a a wavetable oscillator for his IBM 7094 based Music II program. It's use for electronic music synthesis was written about by Hal Chamberlin in Byte magazine's September 1977 issue.[1] Wolfgang Palm of Palm Products GmbH (PPG) developed it in the late 1970s[2][3] and published in 1979.[4]

Wavetable synths

Wavetable synthesis has been the primary synthesis method in synthesizers built by PPG and Waldorf Music, has been used for the Blacet/Wiard Mini Wave, the Ensoniq ESQ1 and SQ-80, the Kawai K3, the Korg DW8000 and synths developed by Paula Maddox. It has also been used in synths by Sequential Circuits, Access Music, Dave Smith Instruments and Yamaha.

Principle

Wavetable synthesis is periodic reproduction of a single-cycle waveform.[5] The distinction from other synthesis methods employing single-cycle waveforms is that multiple single-cycle waveforms are used and some means of amplitude modulation and mixing the single-cycle waveforms is employed.

Both variable and (more commonly) fixed sample rate systems are used[6] and the wave modulation rate is usually significantly smaller (slower) than the sample rate. Depending on the details of the actual implementation, the sound produced by wavetable synthesis may also contain recognizable artifacts, especially aliasing, quantization errors, and phase truncation noise.

A wavetable is a store of single-cycle waveforms. Together with the wave modulation, the wavetable defines the basic sound, which is then often altered by additional post-processing like filtering. The structure of a wavetable, that is, the number and length of entries, depends on the actual implementation. The individual waveforms and their placement in the wavetable have to follow the musical intent as well as the modulation capabilities of the synthesis engine.

Since all waveforms used in wavetable synthesis are periodic, the time-domain and frequency-domain representation are exact equivalents of each other and both can be used simultaneously to define waveforms and wavetables.

Comparison with other digital synthesis techniques

Unlike additive synthesis which generates and adds multiple harmonics, in wavetable synthesis, the waveform is precomputed from the harmonics and stored as wavetables that are used during synthesis.

  • Sample-based synthesis uses multiple-cycle waveforms and intricate algorithms for pitch-shifting.
  • LA synthesis uses short PCM samples for the attack portion of the sound, with either a digital subtractive synth sound or looped samples (most of them single-cycle loops) for the sustain/release portion of the sound.
  • Granular synthesis uses many overlapping windowed samples. While these samples are very short, they are never periodic.

In practice

During playback, the sound produced can be harmonically changed by moving to another point in the wavetable, usually under the control of an envelope generator or low frequency oscillator but frequently by any number of modulators (matrix modulation). Doing this modifies the harmonic content of the output wave in real time, producing sounds that can imitate acoustic instruments or be totally abstract, which is where this method of sound creation excels. The technique is especially useful for evolving synth pads, where the sound changes slowly over time.

It is often necessary to 'audition' each position in a wavetable and to scan through it, forwards and backwards, in order to make good use of it, though selecting random wavetables, start positions, end positions and directions of scan can also produce satisfyingly musical results. Most wavetable synthesizers also employ other synthesis methods to further shape the output waveform, such as filters, phase modulation, frequency modulation and ring modulation.

DIY wavetable synths

References

This page uses Creative Commons Licensed content from Wikipedia:Wavetable_synthesis (view authors).

  1. ^ A sampling of techniques for computer performance of music by Hal Chamberlin, Byte, September 1977
  2. ^ PPG Wave 2.2 owners manual
  3. ^ Part 4 "Digital Age" on Wolfgang Palm's blog
  4. ^ A New Way in Sound Synthesis by Uwe Andresen, Audio Engineering Society (AES), 62nd AES Convention (Brussels, Belgium), 1979
  5. ^ Wavetable Synthesis 101, A Fundamental Perspective by Robert Bristow-Johnson, Audio Engineering Society (AES), 101st AES Convention (Los Angeles, California), 1996
  6. ^ Practical Considerations in the Design of Music Systems using VLSI by J. William Mauchly, Albert J. Charpentier, Audio Engineering Society (AES), AES 5th International Conference: Music and Digital Technology, 1987

Further reading

  • Theory and Techniques of Electronic Music by Miller Puckette, World Scientific Publishing Company, 2007, chapter 2
  • Wavetable Synthesis 101, A Fundamental Perspective by Robert Bristow-Johnson
  • Sound Synthesis and Sampling by Martin Russ, chapter 3.2, Focal Press, 2nd edition, 2004, ISBN 0-240-51692-3

External links

Other wikis