Introduction to synthesis Flashcards
What are the three stages of a typical synth?
Oscillator, Filter, Amplifier
Describe the Oscillator.
Signal Generator (creates the wave – sine, saw, etc.)
Describe the Filter.
Change Frequency Content (LPF, HPF, BPF, Slope, Resonance, etc.)
Describe the Amplifier.
Change Amplitude (i.e. varied over time – envelopes, etc.)
As well as signal generators, what can oscillators be used as?
Signal modulators – used to control a variable (e.g. low-frequency oscillators, or LFOs)
How can oscillators be combined?
- Additive synthesis adds sine waves together (as harmonics or partials) to build up complex tones.
- Subtractive synthesis uses complex tones to generate many harmonics, which are then filtered.
How do analogue synths add richness to a synth voice?
Combining several types of wave together.
Describe the audio signal and LFO of a sine wave.
Audio signal = pure, flute like
LFO = gentle, and/or gradual change
Describe the audio signal and LFO of a sawtooth wave.
Audio signal = buzzy, nasal quality
LFO = falling attack (rising reverse-attack) shapes
Describe the audio signal and LFO of a pulse/square wave.
Audio signal = square: hollow, clarinet-like, sometimes buzzy. pulse: varies from hollow to thin.
LFO = alternates between two states (a high value and a low value) - also useful as trigger signals.
Describe the audio signal and LFO of a triangle wave.
Audio signal = hollow like a square wave but less bright
LFO = Gentle and/or gradual change but sharper changes than sine at maximum and minimum
Describe the audio signal and LFO of noise.
Audio signal = ‘sss’ sound (white noise), ‘shh’ sound (pink noise).
LFO = random variations of a setting.
What do filters modify?
Filters modify the frequency characteristic of a input signal – adding to, or taking away from, a range of frequencies within the overall sound
What are filters the basis of?
Subtractive synthesis
What does the cutoff frequency in a LPF and HPF define?
What ‘high’ and ‘low’ frequencies are filtered. The cutoff is defined as where the amplitude has fallen by 3dB.
What are shelving filters used to alter?
- High and low shelving filters used to alter high and low frequencies respectively
- They either boost or cut some of the signal
(most “bass” and “treble” controls are of this type)
What do band pass filters allow?
Band-Pass Filters allow a band of frequencies through around a centre frequency (Fc)
What do band-stop filters stop?
Band-Stop (or Band Elimination, or Band Reject) Filters similarly remove a band of frequencies
What do peaking/notch filters do?
Peaking (or notch) filters boost (or cut) around a centre frequency, without cutting other frequencies.
The “sharpness” of the filter is defined by the Q factor. High values of Q are sharper.
How are amplifiers used in synthesisers?
In synthesisers, amplifiers are used to make a sound more interesting by varying amplitude over time.
What part of an oscillator does an LFO control?
Frequency (pitch) - (like Vibrato, where violinists rock the finger to waver pitch)
What part of a filter does an LFO control?
cutoff frequency - (like Wah-wah, on guitars or the human voice)
What part of an amplifier does an LFO control?
gain (like Tremolo, where woodwind players vary breath strength).
What do envelopes control?
They control the change of a parameter over time (e.g. amplitude, frequency, filter)
How are envelopes different to oscillators?
Unlike oscillators, which are periodic and never actually start or end (they repeat), envelopes have a start and an end, but can have looped sections.
What does an amplitude envelope represent?
An amplitude envelope simply represents the way in which the overall level of a sound (e.g. a note) varies over time ..
Describe a pitch envelope.
The way in which pitch changes over the duration of a sound (e.g. initially rising)
Describe a filter envelope.
May control filter cutoff or resonance.
Describe a panning envelope.
How the spatialisation (e.g. left/right balance changes over time)
What is one of the simplest envelopes?
A ramp. It starts at some arbitrary maximum amplitude and ramps to zero (e.g. fades outs).
How are envelopes best described in synthesis?
By using breakpoint envelopes - Breakpoint envelopes consist of a series of points (time vs. value) which describe the shape of the envelope over time.
To be edited, they require a graphical UI.
What is the most common form of breakpoint interpolation?
The most common form of interpolation is linear (straight lines), but other forms use curves and can have a significant effect:
Exponential, Logarithmic, Cubic, Sine
