Novation Bass Station II - Manual (Page 9)

9
Having shown that just three elements may define 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
define 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 (filtering) or enhancing certain of the harmonics. Lastly, the filtered signal is fed
into the Amplifier, which determines the final volume of the sound.
Oscillators Mixer Filter Amplifier
Additional synthesizer sections - LFOs and Envelopes - provide further ways of altering
the pitch, tone and volume of a sound by interacting with the Oscillators, Filter and
Amplifier, providing changes in the character of the sound which can evolve over
time. Because LFOs’ 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 section 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
keyboard 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 reflect their actual shape when viewed on an instrument called an
oscilloscope, and they are: Sine waves, Square waves, Sawtooth waves, Triangle waves
and Noise. Bass Station II’s Oscillator section can generate all these waveforms.
Each waveform shape (except Noise) has a specific 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
harmonics present in a waveform which determine the tone of the final sound.
Sine Waves
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
These possess just one harmonic. A sine waveform produces the “purest” sound because
it only has this single pitch (frequency).
Triangle Waves
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
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
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
These are rich in harmonics, and contain both even and odd harmonics of the fundamental
frequency. The volume of each is inversely proportional to its position in the harmonic
series.
Square / Pulse Waves
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
These contain only 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 an equal amount of time in its ‘high’
state as in 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.
Bass Station II lets you 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
modulator, 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.
A pulse waveform sounds the same whether the duty cycle is – for example - 40% or 60%,
since the waveform is just “inverted” and the harmonic content is exactly the same.
50%
40%
10%
60%
Noise
Noise is basically a random signal, and has no one fundamental frequency (and therefore
no pitch property). All frequencies are present in noise, and all have the same volume.
Because it possesses no pitch, noise is often useful for creating sound effects and
percussion type sounds.
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
Ring Modulation
A Ring Modulator is a sound generator that takes signals from two oscillators and
effectively “multiplies” them together. Bass Station II’s Ring Modulator uses Oscillator 1
and Oscillator 2 as inputs. The resulting output depends on the various frequencies and
harmonic content present in each of the two oscillator signals, and will consist of a series
of sum and difference frequencies as well as the frequencies present in the original signals.
OSC 1
OSC 2
X