Glossary
From Interactive Audio Wiki
Additive synthesis Additive synthesis (sometimes referred to as Fourier synthesis, as it is based on Fourier’s theorem) refers to the creation of a sound wave by adding together simpler sound waves (typically sine waves). Theoretically, additive synthesis was capable of producing any sound, but the sounds of instruments were still difficult to mimic, due to their complexity. Additive synthesis chips were popular in the Kawai K5 and K5000 series keyboards, though they never gained much general usage. Atari for a time built an additive synthesis chip known as AMY.
Bit A bit, derived from binary digit, is the smallest unit of information in computer language, a one (1) or zero (0). The number of bits typically indicates how much data a computer’s main processor can manipulate simultaneously. It can also be used to describe sound fidelity or graphics. In sound, an 8-bit sound is comparable to AM radio, and 16-bit sound comparable to CD quality. Byte a unit of computer data made up of eight bits.
Cutscene An intermission or break in a game, often used as a reward for solving a particularly difficult part of a game, and is generally non-interactive: the player sits back and watches.
DAC Digital Analog Conversion - The method of converting digital data to analog data (as in analog sound to digital sound). Frequency, the technical name for pitch, is a measure of the number of pulses in a given space of time. It is measured in Hertz, or CPS (cycles per second). For example, a note with a frequency of 440 Hz (A), means that in one second, 440 pulses occur.
Frequency Modulation (FM) synthesis was designed by John Chowning at Stanford University in the early 1970s, and eventually licensed and improved upon by Yamaha, who would use the method for their computer sound chips, as well as the DX series of keyboards. FM uses a modulating (usually sine) wave signal (by selecting a modulating index) to change the pitch of another wave (known as the carrier). Each FM sound needs at least two signal generators (oscillators), one of which is a carrier wave and one of which is the modulating wave. Many FM systems used four or six oscillators for each sound (or voice): the Yamaha DX7 used six oscillators per voice. An oscillator could also be fed back upon itself, modulating its original sound.
Generator: An oscillator is capable of either making an independent tone by itself, or of being paired up cooperatively with its neighbour in a pairing known as a 'generator'. To create realistic musical sounds two sorts of generators are needed 1) oscillators to produce the basic waveform and 2) envelope generators to change the waveforms as the notes age.
LA (Linear Arithmetic) Synthesis: The Roland MT-32 used a form of wavetable synthesis known as Linear Arithmetic, or LA synthesis. Essentially, what the human ear recognises most about any particular sound is the attack transient. LA based synthesisers used this idea to reduce the amount of space required by the sound by combining the attack transients of a sample with simple subtractive synthesis waveforms. This was known as cross modulation.
Oscillator: An oscillator is an electric signal which generates a repeating shape, or wave form. Sine waves are the most common form of oscillator.
Pink noise Pink noise is a variant of white noise. Pink noise is white noise that has been filtered to reduce the volume at each octave. This is done to compensate for the increase in the number of frequencies per octave. Each octave is reduced by 6dbs, resulting in a noise sound wave that has equal energy at every octave . It is commonly used for rain sounds in games, sounding a bit like white noise with more bass.
Polynomial Counter, also known as a Linear-Feedback Shift Register (LFSR). LFSRs are type of binary counter that uses a pseudo-random way of counting, rather than the normal binary incremental/decremental sequences. The number was divided down from the system clock, meaning many pitches were not in tune with others, making it difficult to program melodies.
Programmable Sound Generator (PSG), silicon chips designed for audio applications which generated sound based on the user’s specifications. These specifications were usually coded in assembly language, and early sound programmers and musicians needed to understand programming language to engage the chip.
Pulse Code Modulation (PCM) With PCM (otherwise known as raw, or AI2 synthesis), essentially, an analogue sound is converted into digital sound, by taking many samples—in other words, measuring the amplitude at regular intervals—of an analogue waveform. The data is stored in binary (1s and 0s), which is then decoded and played back as it was originally recorded. The fidelity of the sound depends upon the sample rate or quantisation—the number of bits representing the amplitude. The method is still used, for instance for DVDs or CDs, where the sample rate is 44,100 times per second (44.1 K), or 16-bit. Most early games could only sample at a maximum of 22,050 samples per second. The down side of this method was the amount of space required to store the samples: as a result, most PCM samples were limited to those sounds with a short envelope, such as percussion. Another solution was what is known as adaptive difference PCM (ADPCM). With the ADPCM method, the difference between two adjacent sample values is quantified, reducing the pitch or raising the pitch slightly, to reduce the amount of data required.
Pulse Width Modulation (PWM) PWM modulation works by changing pulse waves by outputting pulses at a constant volume, while the width and spacing of the pulse gives the effect of different frequencies and volumes, controlled by the modulating signal’s amplitude. The PWM method could attain higher volume, and achieve a range of interesting timbres (such as a pseudo-chorus or phasing sound), but the samples were low quality.
Subtractive synthesis starts with a wave form created by an oscillator, and uses a filter to attenuate or subtract specific frequencies and then passes this through an amplifier to control the envelope and amplitude of the final resulting sound. Wavetable synthesis uses pre-set digital samples of instruments, usually combined with basic waveforms of analogue synths. It is therefore much more realistic sounding than FM synthesis, but is much more expensive as it requires the sound card to contain its own RAM or ROM. The Roland MT-32 used a form of wavetable synthesis known as Linear Arithmetic, or LA synthesis. White noise White noise is a sound that contains every frequency within the range of human hearing (generally from 20 Hz to 20 kHz) in equal amounts. Used for laser sounds, wind, surf.
