René Nyffenegger's collection of things on the web
René Nyffenegger on Oracle - Most wanted - Feedback -
 

Sound theory

Abbreviations

Osc Oscillator. An Oscillator generates a shape (waveform). This shape determines the timbre (=characteristics) of the tone.
Kybd Keyboard
LPF Low Pass Filter.
HPF High Pass Filter.
Amp Amplifier (not Ampere; the measure of electrical current).
Env Envelope.
Mod Modulation.
LFO Low Frequency Oscillator: usually used for modulation.
Kybd.Trk. Keyboard Tracking: aka KF (Keyboard Follow) or KS (Keyboard Scaling).
Vel. Velocity : information on how hard an instrument note is struck.
VCO or DCO Voltage Controlled Oscillator or Digitally Controlled Oscillator respectively.
VCF or DCF Voltage Controlled Filter or Digitally Controlled Filter respectively.
VCA or DCA Voltage Controlled Amplifier or Digitally Controlled Amplifier respectively.
ADSR Attack, Decay, Sustain & Release: the typical components of an envelope
LPF low pass filter
CFO Cut off frequency
PWM Pulse width modulation
FM Frequency Modulation
PCM Pulse coded modulation (digitsed waveform) => wave table synthesizer

Filter

A filter removes frequencies from a shape, thus altering the shape and the timbre.
low pass filters (LPF) are the most important filters in substractive synthesis. They let low frequencies pass and block high frequencies.
Parameters: - CFO: The frequency that determines what a low frequency is, is called cut off frequency (cfo)
- response: How abruptly the frequencies are blocked around the cfo.
- resonance: How much the frequencies around cfo are boosted (made louder)
high pass filters (HPF)

Envelope

ADSR

Modulation

Modulation Changes the shape over time.

Filter Sweep

cut off (cfo) of filter is modulated.

Vibrato

LFO applied to the pitch of the VCO.

Wah-Wah

LFO (sine, triangle) applied to the cfo.

Tremolo

LFO (sine, triangle) applied to the amplitude of the vco.
If the LFO's frequency is high (thus not being a HFO anymore), the sound becomes FM.

gated sound

LFO (square) applied to the amplitude of the vco

PWM

Cross Modulation

The pitch of one modulator is modulated by another oscilator. Also called FM. => Bell like sounds

Ring Modulation

Outputs sum and difference of inputs. => gong like sounds

Flanging

A signal is added with itself delayed. The amount of delay is varied over time. The delay should be kept below 20ms because otherwise, it sounds like an echo.
If the delay is oscilated with a high frequency, we get -> Chorus
The delay is usually modulated with a low pass filtered noise signal.
-> ADT (Automatic Double Tracking) occurs when the delay is between 15ms and 30ms. It sounds like two singers.

Comb Filter

A distortion produced by combining an electrical or acoustical signal with a delayed replica of itself. The result is constructive and destructive interference that results in peaks and nulls being introduced into the frequency response. When plotted to a linear frequency scale, the response resembles a comb, hence the name.
Combing a sine wave produces only the fundamental frequency, no matter what the comb frequency, because the comb does not produce its own frequency. However, it can change the amplitude and quality of the sound by giving a "metallic" ring.
Samples that are noise-based seem to work best with the comb filter bank, as they allow all the filters to 'ring through'. Try this effect for 'speaking chords', turning water drops into plucked-strings and other flights of fancy.

Vocoding

=Voice Coding

Links

beginner's synthesizer faq
Sonic Thrill (contains a synthesizer dictionary)
Sound on Sound A music recording magazine (has a synth secret every month.
Synthesizers, Music & Television
Introductino to sound processing book
Digital Waveguide Modeling of Musical Instruments