Subtractive Synthesis: Tone Generation

So let's look at the first stage of subtractive synthesis: tone generation. A tone being generated in a synthesizer will happen via an oscillator. Essentially, this is a device for generating waveforms.

Types of Waveforms

In older analog synths, we had regular or cyclic waveforms such as:

• Sine
• Triangle
• Square
• Sawtooth

Here you can see on the screen what they look like. Computer-based oscillators in other forms of synthesis can actually generate all sorts of different weird and wonderful wave shapes.

Sine Wave

• A sine wave is a pure tone with no harmonics and sounds like a whistle.

Triangle Wave

• A triangle wave contains only odd harmonics; it sounds similar to an organ.

Square Wave

• A square wave is mostly odd numbered harmonics and sounds close to an actual clarinet.

Sawtooth Wave

• A sawtooth wave contains both even and odd harmonics and sounds very close to a saxophone.

Noise Wave

• A noise wave is random and noisy, reminiscent of a waterfall.

In-Depth Waveform Analysis

Diving in a little bit further, let's explore these waveforms:

Sine Wave

• Description: Clean and clear sounding wave.
• Harmonics: Contains only the first harmonic (pure fundamental tone).
• Usage: Creates a pure sound like a whistle.

Sawtooth Wave

• Description: Clear and bright sounding.
• Harmonics: Contains both odd and even harmonics, as well as the fundamental tone.
• Ideal For: Creating sounds like strings, pads, some bass, and brass sounds.

Square Wave

• Description: Hollow and woody sounding.
• Harmonics: Contains a wide range of odd harmonics in addition to the fundamental tone.
• Usage: Useful for creating reed instruments, pads, basses, and can emulate kick drums, congas, tomtoms, and other percussive instruments.

Pulse Wave

• The square wave can be reshaped to make the waveform cycles or pulses more rectangular by using pulse width modulation (PWM).
• The more rectangular the wave becomes, the more nasal it sounds.
• When modulated, the square wave is known as a pulse wave, containing fewer harmonics, which can be great for reed sounds, bass sounds, and brass sounds as well.

Triangle Wave

• Description: Contains only odd harmonics in addition to the fundamental tone.
• Harmonics Roll-off: High harmonics roll off faster than those of a square wave.
• Ideal For: Creating flute sounds, pad sounds, and vocal "OO" sounds.

Noise Waves

Noise waves can usually be split into various categories, two of the most notable being white noise and pink noise.

• White Noise:

  • Contains all frequencies at full level.
  • Some people use this to help them go to sleep.

• Pink Noise:

  • It is filtered noise where the level of higher frequencies is reduced by 3dB per octave.
  • Great for emulating percussive sounds such as snare drums or atmospheric sounds like wind or the sound of the sea.

There are loads of noise wave colors, but we'll focus on white noise and pink noise for our discussion.