User Manual

15
being produced is actually a pure sine wave, the pitch of which depends on the setting of
the Frequency control (the filter’s cut-off point). This resonance-produced sine wave can
actually be used for some sounds as an additional sound source if wished.
The diagram below shows the response of a typical low-pass filter. Frequencies above the
cut-off point are reduced in volume.
Volume
Volume
Frequency
Cut-off
Frequency
Volume
Volume
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
When resonance is added, the frequencies around the cut off point are boosted in volume.
Volume
Volume
Frequency
Cut-off
Frequency
Volume
Volume
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
In addition to the traditional low-pass filter type, there are also high-pass and band-pass
types. On Peak, the filter type is selected with the Shape switch
33
.
A high-pass filter is similar to a low-pass filter, but works in the “opposite sense”, so
that it is frequencies below the cut-off point which are removed. Frequencies above the
cut-off point are passed. When the Frequency parameter is set to minimum, the filter is
completely open and no frequencies are removed from the raw Oscillator waveforms.
Volume
Volume
Frequency
Cut-off
Frequency
Volume
Volume
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
With a band-pass filter, just a narrow band of frequencies centered around the cut-off point
is passed. Frequencies above and below the band are removed. It is not possible to fully
open this type of filter and allow all frequencies to pass.
Volume
Volume
Frequency
Cut-off
Frequency
Volume
Volume
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
Frequency
Cut-off
Frequency
Envelopes And Amplifier
In earlier paragraphs, the synthesis of the pitch and the timbre of a sound was described.
The next part of the Synthesis Tutorial describes how the volume of the sound is controlled.
The volume of a note created by a musical instrument often varies greatly over the duration
of the note, according to the type of instrument.
For example, a note played on an organ quickly attains full volume when a key is pressed.
It stays at full volume until the key is released, at which point the volume level falls instantly
to zero.
TIME
KEY "ON" KEY "OFF"
VOLUME
AT TACK DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
AT TACK DECAY
RELEASE
SUSTAIN
SUSTAIN
RATE
TIME
KEY "ON" KEY "OFF"
VOLUME
AT TACK DECAY
RELEASE
SUSTAIN
SUSTAIN TIME
TIME
KEY "ON" KEY "OFF"
VOLUME
AT TACK DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
AT TACK DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
FILTER
CUT-OFF
A piano note quickly attains full volume after a key is pressed, but gradually falls in volume
to zero after several seconds, even if the key is held.
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY
RELEASE
SUSTAIN
SUSTAIN
RATE
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY
RELEASE
SUSTAIN
SUSTAIN TIME
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
FILTER
CUT-OFF
A string section emulation only attains full volume gradually when a key is pressed. It
remains at full volume while the key is held down, but once the key is released, the volume
falls to zero fairly slowly.
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY
RELEASE
SUSTAIN
SUSTAIN
RATE
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY
RELEASE
SUSTAIN
SUSTAIN TIME
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
VOLUME
ATTAC K DECAY RELEASE
SUSTAIN
TIME
KEY "ON" KEY "OFF"
FILTER
CUT-OFF
In an analogue synthesiser, changes to a sound’s character which occur over the duration
of a note are controlled by a section called an Envelope Generator. One (Amp Env) is
always related to the Amplifier, which controls the note’s amplitude – i.e., the volume of
the sound – when the note is played. Each envelope generator has four main parameters,
which determine the shape of the envelope; these are often referred to as the ADSR
parameters.