Making Music
  Computer Music Software and Hardware

What's that noise

The final waveform we'll look at is noise. This is a hissing, rushing sound similar to what you hear when a TV signal is lost or you tune between radio stations.

Noise comes in several colourful varieties. The most common is white noise which contains all audio frequencies in equal proportions. Pink noise is the next most popular. It contains fewer high frequencies, sounds less hissy and has a rushing sound. You can create an approximation of pink noise by running white noise through a low pass filter (see The Quick Guide To EQ And Filters).

Take away

Tech terms Hertz The tech term for 'cycles per second', named after Heinrich Rudolph Hertz (1857-1894). If a sound source vibrates at 100 cycles per second it has a frequency of 100Hz. Modulator A synth module whose output is used to change another. A So that instruments can play in tune with each other, they must sound the same pitch when they play the same note. In 1939 it was agreed that the A above Middle C should be 440Hz (in the 19th century is had been as low as 435Hz) so use this when setting an oscillator's or synth's pitch.

Analogue synths use a process called subtractive synthesis. You start with one of the waveforms just described and run it through a filter to remove some harmonics - hence subtractive synthesis. Most forms of synthesis are subtractive to some degree - as soon as you add a filter to the process you are going to remove something!

One alternative to subtractive synthesis is additive synthesis which is simply adding waveforms together. If you have enough oscillators - and time and patience! - you can try this by adding sine waves together. Create a sawtooth wave, for example, by mixing sine waves at the frequency and proportion of the harmonics as described above.

Home in on the range

As well as generating waveforms, most oscillators have range and tuning controls. Range sets the octave and traditionally this was calibrated in 'feet', a throwback to the days of organs when the length of an organ pipe determined its pitch. Options will typically be 2', 4', 8', 16' and 32'. Each foot is an octave and 8' is the octave starting at Middle C. Many modern synths calibrate their oscillators in octaves.

Tuning controls fine tune an oscillator to a specific pitch. Many oscillators have coarse and fine tuning controls. In the early days of analogue synths, oscillators were notoriously unstable and kept drifting out of tune. They were often switched on hours before a performance to let them stabilise but the musician would often be playing it with one hand and tuning it with another.

Modern instruments are far more stable and digital synths and software should never have tuning problems. However, it's common to run two oscillators together and to detune one slightly against the other to thicken the sound.

How low can you go?

We've been talking about oscillators as sound sources but they can be used as modulators, too. The LFO (Low Frequency Oscillator) is simply an oscillator that oscillates at a low frequency. It could be so low that it takes several seconds or even minutes to complete a cycle.

LFOs are typically used to add vibrato to a sound by applying a sine wave at a frequency of around 5-8Hz to the pitch. Applying it to volume produces tremolo and applying it to a filter to produce variations in tone.

When selecting an oscillator, it's important to pick one that generates the type of sound you want for your raw material. This overview of oscillators will help you do that..

For more info... Synthesiser documentation should contain information about the oscillators it contains and may we modestly suggest the Quick Guide to Analogue Synthesis.