Intro to Sound Synthesis Test 1

Sine wave (sinusoidal wave)

a simple wave vibrating at a single frequency.

Complex wave

a wave vibrating at multiple frequencies.

Frequency

the rate at which a vibration (or wave oscillation) occurs, typically measured in Hertz (cycles per second).

Amplitude

the maximum absolute value of a periodic (repeating) wave; the height of a wave, primarily experienced as loudness.

Fundamental frequency

the dominant frequency of a complex wave, which is perceived as the pitch and is generally the lowest frequency.

Partial

one of the frequencies that constitutes a complex wave.

Harmonic

a partial that is a whole number multiple of the fundamental frequency.

Octave

a ratio of 2:1 between two frequencies (e.g., an octave above 100Hz is 200Hz, an octave below 100Hz is 50Hz).

Envelope

a curve that describes changes in a characteristic.

ADSR Envelope

a curve that describes changes in a sound (usually in its amplitude) based on its Attack (the amount of time it takes to reach the first peak), Decay (the amount of time between the Attack peak and the Sustain level), Sustain (the level of the sustain in relation to the attack peak), and the Release (the amount of time it takes to return to zero after the noteoff message is sent).

Additive synthesis

sound synthesis in which individual waves (usually sine waves) are simultaneously presented as individual partials.

Low Frequency Oscillator

a device that produces a wave to regularly vary a parameter (most commonly the frequency or amplitude of another wave), generally at a frequency of less than 20 Hz. Frequently abbreviated as LFO.

Tremolo

a regular variation in amplitude (often by means of an LFO).

Vibrato

a regular variation in frequency (often by means an LFO).

Subtractive synthesis

sound synthesis in which the spectrum of a rich audio signal is modified (“subtracted”) by a filtering process. The three stages in a standard subtractive synthesis algorithm are 1) initial audio signal, 2) filter stage, 3) amplifier/amplitude_envelope

Pulse Wave (aka Rectangle Wave)

a waveform in which the amplitude alternates between a minimum steady value and a maximum steady value, with an instantaneous transition between these values. The percentage of each cycle occupied by the maximum value (known as the “duty cycle”) determines the specific characteristics of the spectrum.

Square Wave

a pulse wave with a 50% duty cycle. It is, therefore, a waveform in which the amplitude alternates equally between a minimum steady value and a minimum steady value. This waveform presents only odd harmonics, where the power of each harmonic can be represented as 1/n (where n=the harmonic number), decreasing by 6 dB per octave.

Sawtooth Wave

a waveform whose amplitude ramps upward at a linear rate, then sharply drops. This waveform presents both odd and even harmonics, where the amplitude of the harmonics decreases by 6 dB per octave.

Triangle Wave

a waveform whose amplitude ramps upward and downward at a linear rate. This waveform presents only odd harmonics, where the power of each harmonic can be represented as 1/n² (where n=the harmonic number), decreasing by 12 dB per octave.

Audio Filter

a device that processes audio input by amplifying, passing, or reducing selected frequency ranges.

Low-pass filter

a filter that allows signals whose frequency is below a set cutoff frequency to pass unmodified, but attenuates signals whose frequencies are higher.

High-pass filter

a filter that allows signals whose frequency is below a set cutoff frequency to pass unmodified, but attenuates signals whose frequencies are lower.

Band-pass filter

a filter that allows signals whose frequency is within a set “pass band” (generally determined by a Center Frequency and Resonance value) to pass unmodified, but attenuates signals whose frequencies are above or below this band.

Band reject/Band stop filter

a filter that only attenuates frequencies within a frequency band. This filter type is also known as a notch filter.

Filter Cutoff Freqency

In a lowpass filter, the frequency above which the signal is attenuated. In a highpass filter, the frequency below which the signal is attenuated.

Filter Center Frequency

In a bandpass or bandstop filter, the midpoint of a passband or stopband. In practice, passbands and stopbands are generally defined by a combination of the Center Frequency and Resonance.

Filter Resonance

The amount of emphasis or suppression of a signal around a Cutoff or Center Frequency.

FM synthesis

sound synthesis method in which the frequency of one wave (the carrier wave) is controlled by a separate wave (modulating wave).

Carrier Wave

in modulation synthesis (FM or AM), the wave to be modified through manipulation of its frequency (in FM synthesis) or amplitude (in AM synthesis).

Modulating Wave

in modulation synthesis (FM or AM), the wave that manipulates the frequency (in FM synthesis) or amplitude (in AM synthesis) of a carrier wave.

Harmonicity

A common term for the ratio between the Modulation Frequency and Carrier Frequency in modulation synthesis. Also called M:C ratio (sometimes identified by its inversion, C:M ratio).

Modulation Index

A term to express the amplitude of the modulating wave in modulation synthesis. It is actually the ratio of the modulating wave amplitude to the modulating wave frequency. This accounts for the logarithmic wave we experience frequency changes (i.e., the higher the octave, the greater the frequency change required to detect a pitch change).