Synthesis Tutorial; Elements Of A Sound; Oscillators And Waveforms - Novation KS Rack User Manual

SYNTHESIS TUTORIAL

It is recommended that this chapter is read carefully if Analogue sound
synthesis is an unfamiliar subject. Users familiar with this subject can skip
this chapter and move on to the chapter - MIDI Tutorial on Page 15.

Elements of a sound

To gain an understanding of how a Synthesizer generates sound it is
helpful to have an understanding of the components that make up a
sound, be it musical or non musical.
The only way that a sound may be detected is by air vibrating the
eardrum in a regular, periodic manner. The brain interprets these vibra-
tions (very accurately) into one of an infinite number of different types of
sound.
Remarkably, any sound may be described by just three terms, and all
sounds always* have them. They are :
* Volume
* Pitch
* Tone
What makes one sound different to another is the proportion of these
three qualities initially present in the sound and how these three terms
change throughout the duration of the sound.
With a musical synthesizer, we deliberately set out to have precise control
over these three terms and, in particular, how they can be changed
throughout the duration of the sound. These terms are often given differ-
ent names, Volume is referred to as Amplitude, Pitch as Frequency and
Tone as Timbre.
Pitch
Taking the example of air vibrating the ear drum, the pitch is determined
by how fast the vibrations are. For an adult human, the lowest vibration
perceived as sound is about twenty times a second, which the brain inter-
prets as a bass type sound, and the highest is many thousands of times a
second, which the brain interprets as an extreme treble type sound.
Wave B is twice the pitch of Wave A
Wave A
If the number of peaks in the two waveforms (vibrations) are counted, it
will be seen that there are exactly twice as many peaks in Wave B as in
Wave A. (Wave B is actually an octave higher in pitch than Wave A). It is
the number of vibrations in a given period that determines the pitch of a
sound. This is the reason that pitch is sometimes referred to as frequency.
It is the frequency of the waveform peaks which are counted during a
given period of time.
Tone
Musical sounds consist of several different related pitches occurring
simultaneously. The loudest is referred to as the 'Fundamental' pitch and
corresponds to the perceived note of the sound. Pitches related to the
fundamental are called harmonics. The relative loudness of these har-
monics compared to the loudness of all the other harmonics (including the
fundamental) determines the tone or 'Timbre' of the sound.
Consider two instruments such as a harpsichord and a piano playing the
same note on the keyboard and at equal volume. Despite having the
same volume and pitch, the instruments would still sound distinctly differ-
ent. This is because the harmonics present in a piano sound are different
to those found in a harpsichord sound.
Volume
Volume, which is referred to as the amplitude or loudness of the sound is
determined by how large the vibrations are. Very simply, listening to a
piano from a metre away would sound louder than if it were fifty metres
away.
Elements of a sound - Oscillators and waveforms
Wave B
Time
Wave A is louder than Wave B but is the same pitch
Wave A
Volume
Having shown that just three elements make up any sound, these ele-
ments now have to be related to a Musical synthesizer. It is logical that a
different section of the Synthesizer 'Synthesizes' (or creates) these differ-
ent elements.
One section of the synthesizer, the Oscillators provide raw waveforms
which provide the pitch of the sound along with its raw harmonic content
(tone). These signals are then mixed together into a section called the
Mixer and the mixed oscillator signal is then fed into a section named the
Filter which is responsible for further altering the tone of the sound. It
does this by removing (filtering) certain undesired harmonic frequencies.
Lastly, the filtered signal is fed into a final section, the Amplifier which
determines the final volume of the sound.
Oscillators Mixer
Audio path of the main Synthesizer blocks
Additional synthesizer sections; LFOs and Envelopes provide ways of
altering the pitch, tone and volume of a sound by interacting with the
Oscillators, Filter and Amplifier, providing changes in the character of
the sound which can evolve over time. Because LFOs and Envelopes
only purpose is to control (modulate) the other synthesizer sections, they
are commonly known as 'modulators'.
These various synthesizer sections will now be covered in more detail.

Oscillators and waveforms

The Oscillator is really the heartbeat of the Synthesizer. It generates an
electronic wave (which creates the vibrations). This Waveform is pro-
duced at a controllable musical pitch, initially determined by the note
played on the keyboard or contained in a received MIDI note message.
The initial distinctive tone or timbre of the waveform is actually determined
by the wave's shape.
Many years ago, pioneers of musical synthesis discovered that just a few
distinctive waves contained many of the most useful harmonics for musi-
cal synthesis. The names of these waves reflect their actual shape when
viewed on an instrument known as an Oscilloscope, and are known as,
Sine waves, Square waves, Sawtooth waves, Triangle waves and Noise
Waves.
Each one has a specific fixed amount of musically related harmonics
(except noise waves) which can be manipulated by further sections of the
Synthesizer.
• •
9
Wave B
Amplifier
Filter