Roland V-Synth Book page 4

Column
Randomly moving controls on the panel or changing parameters in the menus is not the best method of arriving at musically useful sounds. Before attempting to create
new sounds on your V-Synth, you should be aware of some fundamental audio principles and how these apply to synthesizers in general. The concepts and examples
in this section have been kept relatively basic for readers with little or no previous experience of synthesizers.
What is Sound?
Throughout our lives we are constantly surrounded by sounds of all kinds.
Physically, sound waves are contractions and expansions in the air, rapid changes
in air pressure which cause our ear-drums to vibrate (like a microphone capsule)
and send corresponding signals to the brain. The physical attributes of a sound
wave determine how it is perceived, and the three elements we can all recognize
are pitch, brightness and volume (loudness).
Pitch
The pitch of a note depends upon how rapidly the wave repeats itself. A more
scientific and general term for pitch is frequency, measured in Hertz (Hz). 1Hz
is defined as 1 cycle (repetition) per second.
Higher frequency notes have higher pitch. Doubling or halving the frequency of
a note shifts the pitch up or down an octave - the most harmonic interval of all.
For example, the note A4 (middle A) has a standard frequency of 440 Hz, so
A5 is 880 Hz and A3 is 220 Hz.
1 Hz sound wave
(=880 Hz)
(=440 Hz)
time
1 second
(=220 Hz)
Brightness
The brightness of a wave is generally
determined by how complex it is. The less
smooth the waveform, the brighter it
sounds. If you compare a piano waveform
with a sinewave using an oscilloscope, it is
easy to see why the piano note sounds
brighter than the sine wave.
Volume
The volume of a sound is determined by its amplitude, which is basically the
absolute difference between peaks and troughs in the wave i.e. its height in the
diagram below. Louder sounds have higher amplitude, and softer sounds have
lower amplitude.
time
loud sound
Un d e r s t a n d i n g S o u n d 1
A5
time
A4
time
A3
time
Piano waveform (complex)
Sine waveform (smooth)
time
soft sound
Manipulating Partials
A mathematician called Fourier once proved that any sound at all, from a dog
barking to the complete works of Rachmaninov, can be described as a time-
variant mixture of many sine waves known as partials or overtones. A very
large number of sinewave oscillators, each with independent control of
frequency and amplitude would be necessary to emulate even a dog barking.
That is why this additive synthesis is much less common than subtractive
synthesis - selectively removing partials from complex waveforms.
Nevertheless, viewing a complex waveform as the sum of its component partials
is useful to understand how subtractive synthesizers work. The typical sawtooth
and square waves in any subtractive synthesizer consist of a fundamental (the
basic frequency) plus integer multiples of this frequency (2x, 3x ... and so on).
Such integer multiples are called harmonic partials, while the non-integer
multiples particularly prominent in drums or natural (non-instrumental) sounds
are called inharmonic partials.
Sawtooth wave
"clang"
time
Filters
The more high-frequency partials there are in a sound, the brighter it will be.
Removing some of the higher partials from bright waveforms using a Low Pass
"poooh"
Filter will make the sound mellower, and this is the basic method used in
time
subtractive synthesis. Many subtractive synthesizers have an optional High Pass
filter to remove lower partials and/or a Band Pass filter to remove high and low
partials at the same time, leaving those in the middle unaffected. Whatever types
of filter are used, all subtractive synthesizers need waveforms with a rich
assortment of partials so that sounds can be modified in interesting ways.
bright waveform
Before being sent through the filter, additional partials can be created using
several methods of interaction between oscillators e.g. synchronisation (Sync),
Ring Modulation (RM) or Frequency Modulation (FM), as well as various
distortion techniques.
Square wave
time
Partials
Low Pass Filter
level
partials
which are cut
time
frequency
Higher partials are cut,
making the waveform more rounded (mellow)
time
time
Partials
to p.38