9
Volume
Volume, which is often referred to as the amplitude or loudness of the sound is determined
by how large the vibrations are. Very simply, listening to a piano from a metre away would
sound louder than if it were ifty metres away.
Having shown that just three elements may deine any sound, these elements now have to
be related to a Musical synthesizer. It is logical that a different section of the Synthesizer
‘synthesizes’ (or creates) these different elements.
One section of the synthesizer, the
Oscillators
, provide raw waveform signals which
deine the pitch of the sound along with its raw harmonic content (tone). These signals
are then mixed together in a section called the
Mixer
, and the resulting mixture is then fed
into a section called the
Filter
. This makes further alterations to the tone of the sound, by
removing (iltering) or enhancing certain of the harmonics. Lastly, the iltered signal is fed
into the
Ampliier
, which determines the inal volume of the sound.
Additional synthesizer sections -
LFO
s and
Envelopes
- provide further ways of altering
the pitch, tone and volume of a sound by interacting with the
Oscillators
,
Filter
and
Ampliier
, providing changes in the character of the sound which can evolve over time.
Because
LFO
s’ and
Envelopes
’ only purpose is to control (modulate) the other
synthesizer sections, they are commonly known as ‘modulators’.
These various synthesizer sections will now be covered in more detail.
The Oscillators And Mixer
The Oscillator is really the heartbeat of the Synthesizer. It generates an electronic wave
(which creates the vibrations when eventually fed to a loudspeaker). This Waveform is
produced at a controllable musical pitch, initially determined by the note played on the key-
board or contained in a received MIDI note message. The initial distinctive tone or timbre of
the waveform is actually determined by the waveform’s shape.
Many years ago, pioneers of musical synthesis discovered that just a few distinctive
waveforms contained many of the most useful harmonics for making musical sounds. The
names of these waves relect their actual shape when viewed on an instrument called an
Oscilloscope, and these are: Sine waves, Square waves, Sawtooth waves, Triangle waves
and Noise.
Each waveform shape (except noise) has a speciic set of musically-related harmonics
which can be manipulated by further sections of the synthesizer.
The diagrams below show how these waveforms look on an oscilloscope, and illustrate the
relative levels of their harmonics. Remember, it is the relative levels of the various harmon-
ics present in a waveform which determine the tone of the inal sound.
Sine Waves
These possess just a single harmonic. A sine waveform produces the “purest” sound
because it only has its single pitch (frequency).
Triangle Waves
These contain only odd harmonics. The volume of each decreases as the square of its
position in the harmonic series. For example, the 5th harmonic has a volume 1/25th of the
volume of the fundamental.
Sawtooth Waves
These are rich in harmonics, and containing both even and odd harmonics of the fun-
damental frequency. The volume of each is inversely proportional to its position in the
harmonic series.
Square / Pulse Waves
These only have odd harmonics, which are at the same volume as the odd harmonics in a
sawtooth wave.
It will be noticed that the square waveform spends equal amounts of time in its ‘high’ state
and its ‘low’ state. This ratio is known as the ‘duty cycle’. A square wave always has a duty
cycle of 50% which means it is ‘high’ for half the cycle and ‘low’ for the other half.
In the Ultranova, it is possible to adjust the duty cycle of the basic square waveform to
produce a waveform which is more ‘rectangular’ in shape. These are often known as Pulse
waveforms. As the waveform becomes more and more rectangular, more even harmonics
are introduced and the waveform changes its character, becoming more ‘nasal’ sounding.
The width of the pulse waveform (the ‘Pulse Width’) can be altered dynamically by a modu-
lator, which results in the harmonic content of the waveform constantly changing. This can
give the waveform a very ‘fat’ quality when the pulse width is altered at a moderate rate.
It does not make any difference to how a
pulse waveform sounds whether the duty
cycle is 40% or 60%, since the waveform is
just “inverted” and the harmonic content is
exactly the same.
Volume
A
B
Oscillators
Mixer
Filter
Amplifier
Volume
Harmonic
1
Sine Wave
Volume
Harmonic
1
3
5
7
Triangle Wave
Sawtooth Wave
Volume
Harmonic
1
2
3
4
5
Square Wave
Volume
Harmonic
1
2
3
4
5
50%
40%
10%
60%
