Oscillator, Filter, Amplifier, Envelope, and LFO

Oscillator

The oscillator (or VCO, voltage-controlled oscillator) is essential to any synthesizer as it is the module that generates the sound according to a waveform. The waveform is specified as a parameter and shapes the timbre of the sound. The most common waveforms are Sine, Sawtooth, Square, Triangle and Noise.

  • Sine Wave – Energy at a single frequency. Sounds like a single tone that stays even throughout.
  • Saw Tooth Wave – A brighter, more vibrant sound caused by the introduction of upper melodic partials.
  • Square Wave – Generates a hollow sound caused by the missing even upper partials. Square wave only contains odd harmonic partials.
  • Triangle Wave – Similar to the square wave. However, the upper partials seem to disappear (roll-off) faster than that of a square wave.
  • Noise Wave – Energy distributed across the frequencies resulting in a sound like what you hear when the television cable is out.

Filter

The most commonly-used filter is the low-pass filter (LP in phasex), as synth waveforms tend to be very “bright”. Other common filters include the high pass (HP), band pass (BP), notch and comb. The cutoff frequency and resonance are important parameters in a filter. The cutoff frequency is exactly what it sounds like: the frequency at which the filter decreases the level of the signal. The resonance is the level of the frequency at the cutoff frequency, often used to make a peak at the frequency that allows additional harmonics into the sound.

  • Low Pass Filter – From the name, allows the low frequencies to pass through. This is actually good since sounds produced by an oscillator tend to be very bright and brilliant. A Low Pass Filter evens out the perceived spectrum by cutting the highs.
  • High Pass Filter – From the name, allows the high frequencies to pass through.
  • Band Pass Filter (Notch Filter) – This filter allows a range of frequencies to pass through. Filter plugins usually have a knob that allows the user to set a range of what frequencies can pass through.
  • Comb Filter – A special kind of filter that adds a delayed version of the signal to itself, resulting in a cancellation of frequencies. Filter shape resembles that of a comb.

Amplifier & Envelope

The amplifier acts as a preamp for the signal. Amplifiers typically include an ADSR envelope to further shape the sound. ADSR stands for the attack, decay, sustain and release parameters of an envelope.

  • Attack – the amount of time for the note to reach its full power
  • Decay – the amount of time it takes for the note to reach its sustain level from the highest point
  • Sustain – the level at which the note holds
  • Release – the time it takes for the note to fade out

LFO

The LFO (low frequency oscillator) is another type of oscillator that oscillates in a frequency range below that of human hearing. As such, the LFO is not used to generate sounds but to modulate them, often used to create a vibrato or tremolo-like sound.

LFO shapes:

  • Triangle
  • Sawtooth Up
  • Sawtooth Down
  • Square
  • Random (Noise)

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