Photo by Kevin William Deighton on Dolmen Editing
Synthesizers have been a part of popular culture for half a century and it would be impossible to imagine modern music without them. There is barely a genre of music that hasn’t been touched by the vast range of sounds they are capable of producing.
From experimental and avant-garde beginnings to the very centre of contemporary music, synthesizers have a long and fascinating history. But, we’re not here to talk about that.
Have you ever wondered how they work? Whether you’re involved in sound design or music production, read on to discover the basics of synthesizers.
One instrument with many parts
Unlike a piano which produces one complex but fairly consistent sound, the array of sounds a synthesizer can produce are incredibly diverse and more importantly, customizable. In fact, the very point of a synthesizer is sound experimentation, the creation of interesting and unique noises.
Synthesizers usually consist of a few elements, which are often called modules (e.g., oscillators, amplifiers, envelopes), that use voltage signals in unique ways to shape the overall sound. These can be contained in a single instrument or, in the case of modular synthesizers, many small instruments connected together.
The audio signal can pass through or be affected by the different modules in a variety of ways to create interesting and sometimes unexpected results.
Where does the sound originate?
Though there are other types of synthesis, many of the best known synthesizers are designed on the principle of subtractive synthesis. This simply means that you begin with a sound that is rich in harmonics (that contains interesting artifacts other than the simple frequency or pitch) and remove or subtract frequencies to create new sounds.
The voltage controlled oscillator or VCO is where this sound is generated. A VCO creates a waveform (such as sine, square, saw) whose frequency is controlled by the voltage supplied to it. The frequency of a waveform is the pitch or note we hear. Low frequencies produce low pitches and high frequencies produce high pitches.
The most common waveforms are sine, triangle, square and sawtooth, or a combination of these. They are known as periodic waves because their characteristics, such as shape and harmonics, do not alter. They repeat perfectly each time, giving a consistent and pure tone.
1V per octave
Many synthesizers are designed on the 1V per octave system where each additional volt of power supplied to the VCO produces a note one octave higher than the last. For example, the pitch produced by an input of 3V is exactly one octave above the pitch produced by 2V, and so on.
Each volt is then split into 12 divisions to produce the individual notes of an octave. When a key of a keyboard is pressed, it sends this unique voltage “message” and makes the VCO oscillate at a specific frequency or note.
Control voltage or CV is the electrical signal that is used to communicate between our different modules. CV can come from a keyboard, sequencer or other module, and often controls two parameters – pitch and gate. The pitch CV goes into a VCO and controls which note is produced, and the gate goes into an envelope generator that controls the note length.
CV for pitch control sends a wide range of voltages that correspond to different notes. The CV for gate control only sends two voltages – on and off.
Pressing a key, for example, will create a positive voltage (e.g., +5V), which will open our envelope generator. When the key is released, the voltage drops to zero and the envelope closes.
The gate signal is sent to an envelope generator to tell our notes when and for how long we want them to play. A VCO produces sound continuously, but that is not very useful to us. We need to use the envelope to limit the sounds output. An envelope doesn’t affect the VCO directly, but the amplifier or Amp at the very end of our signal chain.
An envelope generator usually has four alterable parameters – attack, decay, sustain and release. A gate “on” signal (note from a keyboard, sequencer) triggers the attack stage of our envelope, which brings the amplifier (volume) up from zero to its highest velocity. Then a period of decay occurs, where the sound transitions usually to a slightly lower volume.
When the lower volume is reached, the envelope holds the amp at this level. This is the sustain period. When the gate signal switches “off” (keyboard note is released), the envelope enters the release period and turns the amp back down to zero.
Now we know how to control the pitch and note duration on a synthesizer, we can get into the really fun stuff. Filters remove frequencies from the pure but monotonous sound wave produced by the VCO. This can be low frequencies, high frequencies or specific frequencies from anywhere on the frequency spectrum.
The three most common types of filter are high pass filters, known as HPFs, low pass filters or LPFs, and band pass filters, BPFs. LPFs allow low frequencies through and remove the high ones, giving a warm and wooly sound like you may hear underwater or through a wall.
HPFs remove the low frequencies and keep the high ones, creating a thin and brittle sound like an old radio or telephone. BPFs just allow through a narrow band of frequencies in whatever range they are calibrated to.
Filters usually have at least two sweepable controls, one for frequency and one for resonance. Frequency allows us to choose the point on the frequency range we want to begin filtering. Resonance slightly boosts the amplitude of the signal at the filter point to augment the sound.
Filters can also be controlled by envelopes, adding extra texture and movement to the sound.
Modulation is part of what makes synthesizers so fascinating and fun to play with. Modulation simply means that one of the parameters is being altered.
This could be the pitch of a VCO or the frequency of a filter, and this can drastically alter the sound. One of the most common ways to add modulation to your sound is with a low frequency oscillator.
A low frequency oscillator or LFO is just like a VCO. It creates a regular wave but it oscillates at a speed too slow for us to hear.
We can use this wave to control other things though. If we attach it to our Amp, it will turn our volume up and down in a regular pattern creating a tremolo effect. If we use it to modulate our wave type, we can start to build complex and dynamic sounds.
The specific combination of settings that create a unique sound are called patches. This involves all the individual elements you tweaked, tuned and modulated.
The way we patch synthesizers and the sounds we create are our own unique expressions and really where the artistry lies. It's fascinating to observe and manipulate the flow of voltage to create new connections and sounds.
It’s a hobby that encourages experimentation and is immersive and addictive in a good way. You can easily start, now you know the very basics of subtractive synthesis.