Wavetable synthesis

The term wavetable synthesis alludes to a relatively broad range of synthesis methods largely used by commercial synthesisers, ranging from MIDI-keyboards to computer sound cards. Also, expressions such as vector synthesis and linear arithmetic have been brought into play by the synthesiser industry to refer to slightly different approaches to wavetable 

In order to introduce some variance over time, wavecycle oscillators should be used in conjunction with signal modifiers such as envelopes and low-frequency oscillators (LFO). 

The multiple wavecycle approach is similar to that of the single wavecycle. The main differences are that a wavetable may hold more than one cycle of a sound and the samples are usually from recordings of natural instruments, as opposed to synthetically generated waveforms. This is the approach adopted by the manufacturers of most computer sound cards. These cards usually have a bank of recorded timbres in read-only memory (ROM) plus 

Crossfading is an approach which combines elements of multiple wavecycling and sampling. This works by gradually changing the sample outputs from one wavetable by the 

This module allows for the creation of sounds graphically on a sketch pad area where the horizontal axis corresponds to time control and the vertical axis to frequency control. There are three sketching tools available  

For musical sounds, it is common to store Just a loop, or table, of the periodic component of a recorded sound waveform and play that loop back repeatedly. 

Originally called sampling synthesis in the music industry, any synthesis using stored PCM waveforms has now become commonly known as wavetable synthesis. Filters are usually added to high-quality wavetable synthesis, allowing control of spectral brightness as a function of intensity, and to achieve more variety of sounds from a given set of samples. 

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Today, in 1997, sampling wavetable synthesis dominates commercial musical instrument synthesis, in spite of concerted effort on the part of many researchers and companies to replace it with some form of parametric synthesis. 

Note that multisampled wavetable synthesis, phoneme speech synthesis, and diphone speech synthesis all take into account a priori the notion of consonants and attacks, versus vowels and steady states. This allows such synthesis techniques to do the right thing, at the expense of someone having to explicitly craft the set(s) of samples by hand ahead of time. This is not generally possible, or economically feasible, with arbitrary PCM. 

Robert Bristow-Johnson. Wavetable Synthesis 101 A Fundamental Perspective. AES 101 Conference Preprint 4400, 1996. 

In Chapter 2 we looked at concatenative (wavetable) synthesis of music and speech. The idea there was to store pieces of waveforms and join them together in the time domain to make sound. The idea of a loop for periodic sounds (steady state of a trumpet, vowels of speech, etc.) was introduced. One way to... 

It seems reasonable to ask why all of our requirements could not be satisfied by the status quo in synthesis based on prerecorded sounds. Also called Code Modulation (PCM), sampling, or wavetable synthesis, much... 

Wavetable synthesis on a sound card is sometimes hardware based. This means that the MIDI instructions are sent to the card and played back and mixed on the card, which is where the instrument samples (wavetable) are stored. Generally speaking, this is good, since this means that the samples that make up the wavetable do not take up any memory (RAM) on your computer. Many popular sound cards load the wavetable into RAM, which can impede your computer s performance. Some sound cards allow you to replace the samples on the wavetable with other samples, either of your own creation or as created by professionals. Examples of this are Creative Labs and Ensoniq SoundFonts and the more general DLS (DownLoadable Sounds) standard. 

A huge variety of software-based synthesizers are available, including software emulation of FM synthesis, ancient tube organs, classic arena rock synthesizers, some of the hest modem synthesizers from famous manufacturers, and wavetable synthesis. Microsoft has a DirectX SoftSynth included with DirectX/ that is easily and extensively used in Windows applications, including ACID it is optimized to use as few resources as possible. Ultimately, this SoftSynth uses your sound card to produce the actual sound. 

As mentioned, the quality of the MIDI output from ACID does not depend on ACID but on your sound card. Configuring ACID to use the correct MIDI device can he a complicated task. Since wavetable synthesis is often the highest-quality synthesis on a sound card, getting ACID to output wavetable samples properly is important. Unfortunately, wavetable synthesizers often use some of the same circuitry that the sound card needs to play back regular media files, and this can cause conflict. This section is going to discuss how to configure ACID MIDI tracks to get the highest quality and talks about some workarounds for a few potential problems. 

MIDI files nsing even the best wavetable synthesis also tend to sound very clean and flat. This is becanse the samples need to be created to be used in the widest variety of situations. Almost all samples are, therefore, completely devoid of any sense of space or ambience. AQD FX plug-ins can be very nseful in making an artificially perfect and balanced MIDI file sound more natural by adding this sort of space to the track. 

Figure 2.28 The single wavecycle approach to wavetable synthesis...

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