Mixer and Filter
Mixer
To extend the range of sounds that may be reproduced, a typi-chosen and any frequencies below the point are passed and
cal Analogue synthesizer has more than one Oscillator. The A-any above are filtered out. This process of removing harmonics
Station has three independent Oscillators and a separate Noisefrom the waveforms has the effect of changing the sounds char-
Oscillator. acter or timbre.
For flexibility, a mixer section is included so that the amplitude
In practice there is a gradual reduction in the volume of the har-
(volume level) of each of the Oscillators may be adjusted inde-
monics above the cut-off point. How quickly these harmonics
pendently and mixed together to form a harmonically complex
are reduced in volume above the cut-off frequency is deter-
waveform.
mined by the Filter?s slope. This slope is measured in ?volume
OSC1units per octave? Since Volume is measured in decibels this
OSC1 VOLUME
slope is quoted in number of decibels per octave (dB). Typical
values are 12dB or 24 dB per Octave. The higher the number,
MIXER
the faster the harmonics are cut and the more pronounced the
OSC2filtering effect.
OSC2 VOLUME
A further important feature of the Filter is the Resonance con-
INPUT TO
trol. Frequencies at the cut-off point may be increased in vol-
FILTER
OSC3OSC3 VOLUMECOMPLEXume by this control. This is useful for emphasizing certain har-
WAVEFORM
monics of the sound.
MIX OF
OSC1,2 AND 3
Cut offCut off
FilterFrequencyFrequency
VolumeVolume
The A-Station is an Analogue subtractivetype of music synthe-
sizer. Subtractiveimplies that part of the sound is subtracted
Response of a typical lowWhen resonance is added,
somewhere in the synthesis process.
pass filter. Frequenciesfrequencies at the cut off
above the cut off point arepoint are boosted in volume
The Oscillators provide the raw waveforms with plenty of har-reduced in volume
monic content and it is the Filterthat subtracts harmonics in a
controllable manner.
FrequencyFrequency
The Filter in the A-Station is a Low Pass type. A cut-off point is
Synthesis Tutorial10 |
ACEC
