Sampling Wavetable Synthesis

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. 

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. 

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. 

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. 

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. 

Similarly to Karplus-Strong synthesis, the cellular automata lookup table also employs a recirculating wavetable to simulate the behaviour of a vibratory medium. The main difference is that the new sample values of the delay line are computed here by means of cellular automata, rather than by the averaging method. 

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