Future Retro XS - Manual (Page 12)

OVERVIEW OF ANALOG SYNTHESIS
A sawtooth waveform is one of the most complex shapes, since it contains a fundamental frequency and
all harmonics of that frequency. Sawtooth waves are very full sounding and have a unique raspy quality
to them.
In addition to these four common waveshapes, there are other items which can also be used as audio
sources which will be described in more detail later on.
You can mix the waveforms of oscillators and other audio sources, together to create more complex
tones. This method is often referred to as additive synthesis.
The most common way to alter the harmonic content of a waveform, however, is by using a filter. This
is referred to as subtractive synthesis, where instead of adding more harmonics, we are actually taking
away or modifying the harmonic content of the oscillator waveforms and other audio sources.
The filter in the XS provides four filter types: lowpass, highpass, bandpass, and notch.
Each filter does just what it sounds like. With the lowpass filter, low frequencies are allowed to pass
through the filter while higher frequencies are attenuated. A highpass, on the other hand, allows the high
frequencies to pass through the filter while the lower frequencies are attenuated. The point at which
frequencies pass or are attenuated by the filter is determined by the filter’s cutoff frequency, which is
variable over the entire audio range. A bandpass filter allows only the frequencies closest to the filter’s
cutoff frequency to pass through, while attenuating all frequencies higher and lower than the cutoff
frequency. A notch filter has the opposite effect of a bandpass filter, where the harmonics closest to the
cutoff frequency are attenuated while all other harmonics are allowed to pass through the filter.
Each filter type also provides resonance, which boosts the amplitude of the frequencies closest to the
cutoff frequency of the filter. The cutoff frequency can be manually adjusted or animated by the use of
modulation sources. Modifying the harmonic content of your audio sources are key to breathing life into
your sounds and making them interesting.
Amplitude is a term used to describe the level of a waveform, or a sound’s overall volume. The volume
of traditional instruments is usually determined by how hard a surface is struck, a string is plucked, or
the force of air blown through a wind instrument. Synthesizers use amplifiers to boost and attenuate a
sound’s amplitude in a similar fashion to increasing and decreasing the volume on your stereo. All
sounds have their own unique shape of volume. This shape can be described as the envelope. The XS
provides four envelope types to help shape the amplitude of a sound. In essence, envelopes are a way of
automating the volume. The controlling envelope can be defined as having attack, decay, sustain, and
release.
When a note is played, the attack parameter determines the amount of time it takes to go from silence to
the loudest possible volume. Once the loudest volume level is reached, the decay parameter then
determines the time it takes to go from the loudest level back to silence or some other defined level.
This defined level is referred to as sustain. Once the sustain level is reached, the sound will remain at
this volume until the note is released, at which point, the release parameter will determine how long it
takes for the volume to return to silence.
The XS also uses Velocity information, which determines how soft or hard a note is played, to control
the amplitude of sounds. So when a note is played softly, the sound is quieter. And as you play harder,
the sound gets proportionally louder.
And finally, the main volume control is also used to set the overall output level for all sounds.
Pay attention to the everyday sounds all around you and consider the frequencies, harmonic content, and
amplitude it takes to create them. And before long, you too will be able to create any sound imaginable.
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