Muse Research MusePlayer manual v1.0 - Manual (Page 21)

A word about sound synthesis
English 21
A - Analog (or Subtractive) synthesis
Called “Analog” because it was the synthesis you could find on
most of the first analog synthesizers, Analog synthesis starts
out with a waveform rich in harmonics, such as a saw or
square wave, and uses filters to make the finished sound sub-
tracting harmonics, which is why it is accurately referred to
has Subtractive synthesis.
Here are the main substracti-
ve synthesis components :
Oscillators: The device crea-
ting a waveform is usually
called an oscillator. The first
synthesizers used analog
electronic oscillator circuits
to create waveforms. These
units are called VCO's (Voltage Controlled Oscillator). More
modern digital synthesizers use DCO's instead (Digitally
Controlled Oscillators). A simple oscillator can create one or
two basic waveforms - most often a sawtooth-wave - and a
squarewave. Most synthesizers can also create a completely
random waveform - or "noise". These waveforms are very sim-
ple and completely artificial - they hardly ever appear in the
nature. But you would be surprised to know how many diffe-
rent sounds can be achieved by only using and combining
these waves.
Filters: To be able to vary the basic
waveforms to some extent, most syn-
thesizers use filters. A filter is an elec-
tronic circuit that removes harmonics
fromthe original waveform. The Filter
section of a synthesizer may be a VCF
(Voltage Controlled Filter) or DCF
(Digitally Controlled Filter). If you
remove all the harmonics from a com-
plex waveform, you end up with a
pure sine wave. Filters come in the
following types:
•Low-Pass Filters allow low frequencies to pass through unaf-
fected and filters out (or blocks
out) the higher frequencies.
This is controlled by a parame-
ter labelled as "Cut-Off
Frequency" (or "Cutoff" or
"Frequency").
• High-Pass Filters (or HPF). A HPF does the opposite of a LPF.
A High-Pass Filter allows the higher frequencies to pass
through unaffected and filters out (blocks-out) the lower fre-
quencies.
The Cutoff Frequency determi-
nes the position in the harmo-
nic spectrum where the filter
will begin to filter (or cutoff)
the higher overtones (ie fre-
quencies) : some overtones
will be removed - and the
waveform will become more
"rounded". If the Cutoff is set to
a high position, then the timbre will be bright. If the Cutoff is
set to a low position, then the timbre will be dull. In other
words the filter controls the brightness of the sound.
Resonance is where the frequencies at the Cutoff position are
boosted (made louder). When a little resonance is introduced,
the frequencies around the Cutoff are boosted and the filter
begins to exaggerate the frequencies around the cutoff point.
With a lot of resonance, the frequencies around the Cutoff are
emphasized to the point where the filter will produce a dis-
tinct tone, or it will start to "sing" with a pronounced tone at
the cutoff frequency.
Amplifiers and Envelopes: The amplifier section on a syn-
thesizer may be labeled as VCA (Voltage Controlled Amplifier) or
DCA (Digitally Controlled Amplifier). An Amplifier will control
the volume of the waveform in real-time, or give it an
"Envelope" so the sound is controlled in amplitube over time.
Nowadays, there are many variations of envelopes available.
However, the most common envelope has 4 parameters: (1)
Attack time, (2) Decay time, (3) Sustain level, and (4) Release
time. This is usually called ADSR Envelope.Envelopes can also
be used to control other sections of a synthesizer.
LFOs: LFOs, or Low Frequency Oscillators are separate
oscillators in a synthesizer that can be used to control
things like the Filter or Amplitube Enveloped. Tremolo
is a common example of an LFO controlling volume,
where as Vibrato is a good example of an LFO control-
ling the pitch of a sound.
The MiniMoog is a great example of an Analog Synth.