Wavetable synthesis
Encyclopedia
Wavetable synthesis is used in certain digital music synthesizer
s to implement a restricted form of real-time additive synthesis
. The technique was first developed by Wolfgang Palm
of PPG
in the late 1970s
and published in 1979, and has since been used as the primary synthesis method in synthesizer
s built by PPG
and Waldorf Music
and as an auxiliary synthesis method by Sequential Circuits
, Ensoniq
, Korg
, Access and Dave Smith Instruments among others.
. The distinction to other synthesis methods employing single-cycle waveforms is twofold: 1) multiple single-cycle
waveforms are used while 2) one or several wave modulators control the change between those multiple waveforms or mixtures thereof. The wave modulation rate is usually significantly smaller (slower) than the sampling rate.
Depending on the details of the actual implementation the sound produced by wavetable synthesis may also contain recognizable artifacts, especially aliasing
, quantization
, and phase truncation noise.
, however unlike additive synthesis the user does not have to work with single harmonics, since each waveform in a wavetable represents a combination of multiple harmonics.
oscillator, appeared in MUSIC IV-B
. Over time this type of short-memory based oscillator has also become known as wavetable oscillator, which is a degenerate case of wavetable synthesis described above. In wavetable synthesis multiple such single-cycle wavetable oscillators are in use, originally as a table of 64 waveforms with 128 samples each, while the term "wavetable" for this arrangement appeared later in the PPG literature for the PPG Wave
. Both variable and (more commonly) fixed sample rate systems can be used.
and Gravis
' Ultrasound
cards, the term "wavetable" started to be applied as a marketing term to any sound card
that used PCM samples as the basis of sound creation. However, these sound cards did not employ any form of wavetable synthesis, but rather a high-end sampler
and subtractive synthesis system based on technology from the E-mu Emulator
family.
Waveterm or are only present in expensive models like the Waldorf
WAVE. More commonly pre-computed wavetables can be added via memory cards or sent to the synthesizer via MIDI. Today wavetables can be created more easily by software and auditioned directly on the computer. 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.
All types of wavetables can be usefully combined, although the size of the wavetable and the difficulty to set up the required modulations ultimately limits this process.
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. It is worth noting that most wavetable synthesizers also employ other synthesis methods to further shape the output waveform, for example, Subtractive Synthesis (Filters), Phase Modulation, Frequency Modulation and AM (Ring) Modulation.
Synthesizer
A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...
s to implement a restricted form of real-time additive synthesis
Additive synthesis
Additive synthesis is a technique of sound synthesis that creates musical timbre by explicitly adding sinusoidal overtones together.The timbre of an instrument is composed of multiple harmonic or inharmonic partials , of different frequencies and amplitudes, that change over time...
. The technique was first developed by Wolfgang Palm
Wolfgang Palm
Wolfgang Palm was a founder and owner of Palm Products GmbH , and the inventor and creator of various pioneering technical designs for analog and digital synthesizers...
of PPG
Palm Products GmbH
Palm Products GmbH was a highly-regarded manufacturer of audio synthesizers. Founded and owned by Wolfgang Palm, PPG was located in Hamburg, Germany and, for 12 years from around 1975 to 1987, manufactured an acclaimed and eclectic range of electronic musical instruments, all designed by Palm.-...
in the late 1970s
1970s
File:1970s decade montage.png|From left, clockwise: US President Richard Nixon doing the V for Victory sign after his resignation from office after the Watergate scandal in 1974; Refugees aboard a US naval boat after the Fall of Saigon, leading to the end of the Vietnam War in 1975; The 1973 oil...
and published in 1979, and has since been used as the primary synthesis method in synthesizer
Synthesizer
A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...
s built by PPG
Palm Products GmbH
Palm Products GmbH was a highly-regarded manufacturer of audio synthesizers. Founded and owned by Wolfgang Palm, PPG was located in Hamburg, Germany and, for 12 years from around 1975 to 1987, manufactured an acclaimed and eclectic range of electronic musical instruments, all designed by Palm.-...
and Waldorf Music
Waldorf Music
Waldorf Music AG is a German synthesizer company. It was founded on 1 January 2003 to take over the actual business of the Waldorf Electronics GmbH which had become insolvent. Waldorf is best known for its Microwave wavetable synthesizer and Q virtual analogue synthesizer lines.- History :Waldorf...
and as an auxiliary synthesis method by Sequential Circuits
Sequential Circuits
Sequential Circuits Inc. was a California-based synthesizer company that was founded in the early 1970s by Dave Smith and sold to Yamaha Corporation in 1987. The company, throughout its lifespan, pioneered many groundbreaking technologies and design principles that are often taken for granted in...
, Ensoniq
Ensoniq
Ensoniq Corp. was an American electronics manufacturer, best known throughout the mid 1980s and 1990s for its musical instruments, principally samplers and synthesizers.- Company history :...
, Korg
Korg
is a Japanese multinational corporation that manufactures electronic musical instruments, audio processors and guitar pedals, recording equipment, and electronic tuners...
, Access and Dave Smith Instruments among others.
Principle
Wavetable synthesis is fundamentally based on periodic reproduction of an arbitrary, single-cycle waveformWaveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...
. The distinction to other synthesis methods employing single-cycle waveforms is twofold: 1) multiple single-cycle
waveforms are used while 2) one or several wave modulators control the change between those multiple waveforms or mixtures thereof. The wave modulation rate is usually significantly smaller (slower) than the sampling rate.
Depending on the details of the actual implementation the sound produced by wavetable synthesis may also contain recognizable artifacts, especially aliasing
Aliasing
In signal processing and related disciplines, aliasing refers to an effect that causes different signals to become indistinguishable when sampled...
, quantization
Quantization error
In analog-to-digital conversion, the difference between the actual analog value and quantized digital value is called quantization error or quantization distortion. This error is either due to rounding or truncation...
, and phase truncation noise.
Comparison with other digital synthesis techniques
Wavetable synthesis is closely related to additive synthesisAdditive synthesis
Additive synthesis is a technique of sound synthesis that creates musical timbre by explicitly adding sinusoidal overtones together.The timbre of an instrument is composed of multiple harmonic or inharmonic partials , of different frequencies and amplitudes, that change over time...
, however unlike additive synthesis the user does not have to work with single harmonics, since each waveform in a wavetable represents a combination of multiple harmonics.
- Sample-based synthesisSample-based synthesisSample-based synthesis is a form of audio synthesis that can be contrasted to either subtractive synthesis or additive synthesis. The principal difference with sample-based synthesis is that the seed waveforms are sampled sounds or instruments instead of fundamental waveforms such as the saw waves...
uses multiple-cycle waveforms and intricate algorithms for pitch-shifting. - LA synthesis uses short PCM samples for the attack portion of the sound and looped samples (most of them single-cycle loops) for the sustain/release portion of the sound.
- Granular SynthesisGranular synthesisGranular synthesis is a basic sound synthesis method that operates on the microsound time scale.It is based on the same principle as sampling. However, the samples are not played back conventionally, but are instead split into small pieces of around 1 to 50ms. These small pieces are called grains...
uses many overlapping windowedWindow functionIn signal processing, a window function is a mathematical function that is zero-valued outside of some chosen interval. For instance, a function that is constant inside the interval and zero elsewhere is called a rectangular window, which describes the shape of its graphical representation...
samples. While these samples are very short, they are never periodic.
Confusion with table-lookup oscillators
Practical realizations of this principle often employ digital memory to store samples of the single-cycle waveform (see numerically controlled oscillator). An early non-realtime software implementation, originally called table-lookupLookup table
In computer science, a lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than...
oscillator, appeared in MUSIC IV-B
MUSIC-N
MUSIC-N refers to a family of computer music programs and programming languages descended from or influenced by MUSIC, a program written by Max Mathews in 1957 at Bell Labs. MUSIC was the first computer program for generating digital audio waveforms through direct synthesis...
. Over time this type of short-memory based oscillator has also become known as wavetable oscillator, which is a degenerate case of wavetable synthesis described above. In wavetable synthesis multiple such single-cycle wavetable oscillators are in use, originally as a table of 64 waveforms with 128 samples each, while the term "wavetable" for this arrangement appeared later in the PPG literature for the PPG Wave
PPG Wave
The PPG Wave was an analog / digital synthesizer built by the German company Palm Products GmbH. The PPG Wave used digital waveforms and analog filters and VCAs. The Wave was a combination of a synthesizer and a sequencer, with sequencer relatively advanced with the ability to influence real sounds...
. Both variable and (more commonly) fixed sample rate systems can be used.
Confusion with sample-based synthesis
Starting around 1993, with the introduction of Creative Labs' Sound Blaster AWE32Sound Blaster AWE32
Sound Blaster AWE32 is an ISA sound card from Creative Technology. It is an expansion board for PCs. The Sound Blaster AWE32, introduced in March 1994, was a near full-length ISA sound card, measuring 14 inches in length, due to the number of features included.-MIDI capability:The Sound Blaster...
and Gravis
Gravis
Gravis can have multiple meanings:*Gramin Vikas Vigyan Samiti, an Indian NGO*Advanced Gravis Computer Technology, manufacturer of computer peripherals and joysticks*Gravis, a Slovak music band...
' Ultrasound
Gravis Ultrasound
Gravis UltraSound or GUS is a sound card for the IBM PC compatible system platform, made by Canada-based Advanced Gravis Computer Technology Ltd...
cards, the term "wavetable" started to be applied as a marketing term to any sound card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
that used PCM samples as the basis of sound creation. However, these sound cards did not employ any form of wavetable synthesis, but rather a high-end sampler
Sampler (musical instrument)
A sampler is an electronic musical instrument similar in some respects to a synthesizer but, instead of generating sounds, it uses recordings of sounds that are loaded or recorded into it by the user and then played back by means of a keyboard, sequencer or other triggering device to perform or...
and subtractive synthesis system based on technology from the E-mu Emulator
E-mu Emulator
The Emulator is the name given to a series of disk-based digital sampling keyboards manufactured by E-mu Systems from 1982 until 1990. Though not the first commercial sampler, the Emulator was among the first to find wide use among ordinary musicians, due to its relatively low price and its size,...
family.
Wavetable
In the context of wavetable synthesis a wavetable is a collection of single cycle waveforms. Together with the wave modulation it defines the basic sound, which is then often altered by additional post-processing like filtering. The structure of the 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. The creation of new wavetables was therefore a difficult process unless supported by specialized editing facilities and (near) real-time playback of edited wavetables on the synthesizer. Such editors often require the use of extra hardware devices like the PPGPalm Products GmbH
Palm Products GmbH was a highly-regarded manufacturer of audio synthesizers. Founded and owned by Wolfgang Palm, PPG was located in Hamburg, Germany and, for 12 years from around 1975 to 1987, manufactured an acclaimed and eclectic range of electronic musical instruments, all designed by Palm.-...
Waveterm or are only present in expensive models like the Waldorf
Waldorf Music
Waldorf Music AG is a German synthesizer company. It was founded on 1 January 2003 to take over the actual business of the Waldorf Electronics GmbH which had become insolvent. Waldorf is best known for its Microwave wavetable synthesizer and Q virtual analogue synthesizer lines.- History :Waldorf...
WAVE. More commonly pre-computed wavetables can be added via memory cards or sent to the synthesizer via MIDI. Today wavetables can be created more easily by software and auditioned directly on the computer. 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.
Wavetable Types
Several types of wavetables can be identified by the way they are used or created.- Transient wavetables capture the evolution of harmonics in a sound over time. They are typically modulated with a ramp or envelope generator, sometimes (also) with an LFO. Creation of such wavetables can be done by employing the STFTShort-time Fourier transformThe short-time Fourier transform , or alternatively short-term Fourier transform, is a Fourier-related transform used to determine the sinusoidal frequency and phase content of local sections of a signal as it changes over time....
on a sample with known and constant pitch. - Formant wavetables capture the harmonic changes of sounds played at different pitches through a resonator with fixed resonances. This is most often used for voice-like sounds and requires the wave modulation to follow the playback pitch (often called "keytrack"). Creation of such wavetables requires multiple samples, each with a different pitch.
- Wave Sequence wavetables often have sudden changes in harmonic content and are typically modulated with one or more LFO to provide rhythmic or loop-like sound effects. They are usually created by a process similar to transient wavetables or by an ad-hoc combination of unrelated waveforms or wavetable segments.
- Speech wavetables are a specialized wave sequences and mainly modulated with ramp segments. Creation is usually done with the help of Text-to-SpeechSpeech synthesisSpeech synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware...
synthesis software.
All types of wavetables can be usefully combined, although the size of the wavetable and the difficulty to set up the required modulations ultimately limits this process.
Practical Use
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. It is worth noting that most wavetable synthesizers also employ other synthesis methods to further shape the output waveform, for example, Subtractive Synthesis (Filters), Phase Modulation, Frequency Modulation and AM (Ring) Modulation.