Chapter 4 - 5 - 6
[ Sorry not finished yet ]
CH1('Increasing patch complexity')
CH2('Adding a second VCO')
A synthesizer using only a single oscillator per voice isn't very interesting.
Although the VCF can add timbre changes the cyclic character of the generated wave results
in a rather boring sound. A possible solution is modulating the generated wave of the oscillator.
A often used technique is PWM (Pulse Width Modulation) where the oscillator generates pulse like
waveforms of differing width. By adjusting modulation speed and depth different timbres can be generated.
More sonic variation can be archived by using a second (or more) oscillator(s). Especially analog oscillators
never run on the exact same frequency. The small differences in frequency generates 'beating' sounds. Where the
output of the two oscillators are canceling and amplifing each other. The beating frequency is the difference
in frequency between the oscillators. By applying more as two oscillators the effect is enhanced. Most analog
synthesizers have a 'unison' mode where as much oscillators as possible are played simultaneously, producing
a very 'fat' and rich sound. This is the reason why analog synths are still highly valued in the currently digital
Playing two oscillators together is not the only configuration possible. Some synthesizers have a syncronise input. By
connecting the sync-output or pulse-output of the first oscillator with the sync-input of the second, the two oscillators
will be 'synced'. This means that the second oscillator is forced to restart its wave when the first does so. It cancels any
'beating' between the oscillators even if the two are not running the same frequency. But if the frequency difference is not
harmonic, a raw (distorted gitar?) sound is the result.
There are two types of sync, Hard-sync and Soft-sync. Most common is the hard-sync which always forces the second oscillator
in restart. The soft-sync has a variable 'hardness', where lower setting give less sync moments. The soft-sync allowes the
difference between oscillator frequences to be greater while still syncing. But soft-sync requires stable oscillators and
some patience by setting up the sound.
Frequency modulation (FM) is made populair by Yamaha with the DX7 range of synthesizers. Using the output of
one oscillator to modulate the frequency of an other oscillator, creates a new sound with a wide spectrum.
Increasing the amplitude of the first oscillator increases the spectrum width and therefore increases the
FM effect. The modulating oscillator is mostly named 'modulator', the modulated oscillator is called 'carrier'.
Ofcourse more as two oscillators could be used, with increasing spectrum complexity.
Two principle sounds can be created (with many variants) with two oscillators. The first configuration is used to
create the FM-piano sounds. The oscillators are set to sin-wave outputs and the first oscillator frequency
is set at a multiple or even dividable of the second oscillator. The famous FM-bell like sounds are generated
by setting the oscillators on none relating frequencies. FM is a very rich modulating technique with lot of
room for experimentation. Different waveforms for the modulator and carrier can be used. Multiple modulators
for the same carrier oscillator, or chaining more as two oscillators in a row.
Frequency modulation with a modulator at a very low frequency (<10 Hz) is called vibrato.
CH2('Amplitude modulation (ring modulation)')
Standard amplitude modulation (modulating the volume of one oscillator with a other oscillator) gives
nice organ sounds. But the most interesting use of a ring-modulator is feeding external sound sources
thru. A low sinus frequency oscillator with a human-voice combined in a ring-modulator gives Darlek (Dr. Who)
sounds. Amplitude modulation at a very low frequency (<10 Hz) is called tremelo.
CH1('Effects and analog-digital-hybrids')