A Concise History of Synthesation

~~Lord Larehip~~ · 11-18-2013, 05:49 PM

A tone has three main components that define it: 1. Pitch, 2. Volume, and 3. Timbre. What is timbre? Every tone has a sine wave and an overtone series. This series consists of natural harmonics that accompany the fundamental sine wave. A guitar sounds the way it does due to the accents in its harmonic series. Certain harmonics are accented while others are not. We call this characteristic of sound timbre (pronounced “TAM-ber”). If we pluck the A-string open, the guitar’s timbre is different than a piano A-key in the same octave because the piano’s harmonic series is accented differently. If we take a piano’s overtone series and “freeze” it on a computer screen and then use software to change its overtone accents to be identical to that of a guitar, the note is now indistinguishable from a guitar because it has been altered to mimic a guitar’s timbre. Likewise a guitar’s timbre can be altered to sound identical to a piano’s timbre. And, yes, such software does exist and is, in fact, very common. But before computers, analog synthesizers were doing this electronically.

In analog synthesation, there are seven essential components a synthesizer must have to be worthy of the name:
1. A VCA or voltage-controlled amplifier
2. A VCO or voltage-controlled oscillator (usually two)
3. A filter
4. A volume envelope generator
5. A filter envelope generator
6. A pitch envelope generator
7. An LFO or low frequency oscillator

Most synths have more than these but these seven are fundamental to any synth. A VCA is an amplifier whose gain is controlled by a small applied voltage called a control-voltage. On a digital synth, the amplifier is often DCA or digitally controlled where the amplifier is controlled by a set of binary numbers. In either case, the amplifier determines amplitude.

The VCO is an oscillator controlled by a small applied voltage. It is responsible for pitch. On a digital synth, there is instead a DCO, an oscillator controlled by a set of binary numbers.

The filter controls brightness by slightly varying the timbre. The filter will have an adjustable cut-off point and a resonance adjustment. Resonance accents various frequencies around the cut-off point resulting in unusual effects.

The volume envelope generator generates a set of instructions that it gives to the amplifier to carry out. These instructions appear in the form of a graph depicting the ADSR envelope. ADSR stands for attack, decay, sustain and release. Attack describes how a sound starts off, decay describes how the attack fades, sustain describes how long the sound holds after the decay. Sustain can last as long as the key is held down or can fade arbitrarily or can simply cut off. Release describes how the sound fades away after the sustain period ends. An ADSR envelope graph:

ADSR envelope. The graph is amplitude vs. time. In this graph, the attack rises quickly to a maximum amplitude, decays quickly (albeit somewhat slower than the attack) and then goes into the release which subsides slowly in both amplitude and time. No sustain is shown here but would simply be a horizontal line between the decay and release stages showing how long the signal remained at a steady amplitude before being released.

The filter envelope generator likewise gives instructions to the filter which can be represented with an ADSR graph.

The pitch envelope generator gives instructions to the oscillator. Once again, this can be expressed as an ADSR graph.

The low frequency oscillator came in the 60s when modular synths were introduced and the effect was accidental but was found to be very useful. Today, they are built into synths. The LFO is a secondary oscillator that does not produce a pitch like the VCO. It is much too low to be heard—below the 20 Hz range. Its purpose is to modify the audible sounds in various ways without introducing any sound of its own and hence it is below the threshold of hearing. The LFO is patched to modulate parameters as amplitude (creating tremolo), pitch (creating vibrato), phasing, stereo panning, filter frequency, etc. The LFO is also adjustable to control the amount of modulation. Often, the LFO is not called out on the synth. Instead there will be a tremolo button, for example, that internally patches the LFO to the VCA or DCA when it is engaged.

11-18-2013, 05:49 PM	#1 (permalink)
~~Lord Larehip~~ Account Disabled Join Date: Jun 2013 Posts: 899	A Concise History of Synthesation A tone has three main components that define it: 1. Pitch, 2. Volume, and 3. Timbre. What is timbre? Every tone has a sine wave and an overtone series. This series consists of natural harmonics that accompany the fundamental sine wave. A guitar sounds the way it does due to the accents in its harmonic series. Certain harmonics are accented while others are not. We call this characteristic of sound timbre (pronounced “TAM-ber”). If we pluck the A-string open, the guitar’s timbre is different than a piano A-key in the same octave because the piano’s harmonic series is accented differently. If we take a piano’s overtone series and “freeze” it on a computer screen and then use software to change its overtone accents to be identical to that of a guitar, the note is now indistinguishable from a guitar because it has been altered to mimic a guitar’s timbre. Likewise a guitar’s timbre can be altered to sound identical to a piano’s timbre. And, yes, such software does exist and is, in fact, very common. But before computers, analog synthesizers were doing this electronically. In analog synthesation, there are seven essential components a synthesizer must have to be worthy of the name: 1. A VCA or voltage-controlled amplifier 2. A VCO or voltage-controlled oscillator (usually two) 3. A filter 4. A volume envelope generator 5. A filter envelope generator 6. A pitch envelope generator 7. An LFO or low frequency oscillator Most synths have more than these but these seven are fundamental to any synth. A VCA is an amplifier whose gain is controlled by a small applied voltage called a control-voltage. On a digital synth, the amplifier is often DCA or digitally controlled where the amplifier is controlled by a set of binary numbers. In either case, the amplifier determines amplitude. The VCO is an oscillator controlled by a small applied voltage. It is responsible for pitch. On a digital synth, there is instead a DCO, an oscillator controlled by a set of binary numbers. The filter controls brightness by slightly varying the timbre. The filter will have an adjustable cut-off point and a resonance adjustment. Resonance accents various frequencies around the cut-off point resulting in unusual effects. The volume envelope generator generates a set of instructions that it gives to the amplifier to carry out. These instructions appear in the form of a graph depicting the ADSR envelope. ADSR stands for attack, decay, sustain and release. Attack describes how a sound starts off, decay describes how the attack fades, sustain describes how long the sound holds after the decay. Sustain can last as long as the key is held down or can fade arbitrarily or can simply cut off. Release describes how the sound fades away after the sustain period ends. An ADSR envelope graph: ADSR envelope. The graph is amplitude vs. time. In this graph, the attack rises quickly to a maximum amplitude, decays quickly (albeit somewhat slower than the attack) and then goes into the release which subsides slowly in both amplitude and time. No sustain is shown here but would simply be a horizontal line between the decay and release stages showing how long the signal remained at a steady amplitude before being released. The filter envelope generator likewise gives instructions to the filter which can be represented with an ADSR graph. The pitch envelope generator gives instructions to the oscillator. Once again, this can be expressed as an ADSR graph. The low frequency oscillator came in the 60s when modular synths were introduced and the effect was accidental but was found to be very useful. Today, they are built into synths. The LFO is a secondary oscillator that does not produce a pitch like the VCO. It is much too low to be heard—below the 20 Hz range. Its purpose is to modify the audible sounds in various ways without introducing any sound of its own and hence it is below the threshold of hearing. The LFO is patched to modulate parameters as amplitude (creating tremolo), pitch (creating vibrato), phasing, stereo panning, filter frequency, etc. The LFO is also adjustable to control the amount of modulation. Often, the LFO is not called out on the synth. Instead there will be a tremolo button, for example, that internally patches the LFO to the VCA or DCA when it is engaged.