Novation SUMMIT - Page 19

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generally result in more frequencies being removed than with a single filter section, as
both filters are subtractive. However, interesting results can arise if the two filters have
different cut-off frequencies. For example, if a low-pass filter is followed by a high pass
filter, the low-pass filter will pass only higher frequencies on to the high-pass filter, which
will then remove some of them, leaving a narrow band of frequencies “between” the
cut-off frequencies of the two filters. The width of this band will depend on the difference
between, or “separation of” the two cut-off frequencies.
LPF
(f
1
)
HPF
(f
2
)
LP > HP
f
1
Low pass filter
12 dB/oct
High pass filter
12 dB/oct
Combined
response when
Frequency
Low pass filter
12 dB/oct
High pass filter
12 dB/oct
f
2
f
1
f
2
f
1
< f
2
Combined
response when
f
1
> f
2
Combining the same filters in parallel produces quite a different result, as the responses of
the two sections are effectively summed together. Low frequencies will be passed by the
low-pass filter and high frequencies by the high-pass filter, resulting in a dip or a hump in
the response in the area between the two cut-off frequencies.
LPF
(f
1
)
HPF
(f
2
)
+
f
1
Low pass filter
12 dB/oct
High pass filter
12 dB/oct
f
2
Combined
response when
f
1
< f
2
Frequency
Low pass filter
12 dB/oct
High pass filter
12 dB/oct
f
1
f
2
Combined
response when
f
1
> f
2
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 sections called Envelope Generators. One of these (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. In Summit, each envelope generator has five main
parameters, which determine the shape of the envelope; these are referred to as the
AHDSR parameters, or the envelope “phases”.
VOLUME
TIME
KEY “ON” KEY “OFF”
SUSTAIN
ATTACK HOLD DECAY RELEASEDELAY
Attack Time
Adjusts the time it takes after a key is pressed for the volume to climb from zero to full
volume. It can be used to create a sound with a slow fade-in.
Hold Time
This parameter is not found on many synthesisers, but is available in Summit. It determines
for how long the note’s volume remains at its maximum level following the Attack Time,
before commencing the volume drop set by the Decay Time.