Demystifying Analog

In an era where creative or commercial success is possible without the need for physical hardware beyond a computer running the right application, one could be forgiven for believing there is no longer a need for seemingly antiquated analog technology in music production. However, increasing numbers of musicians are enjoying the unique experience of exploring the distinctive properties and authenticity analog synthesizers have to offer.

While aimlessly tweaking knobs, sliders and switches can unquestionably be fun, it is of course massively advantageous to understand both the core principles at work, and what tools are on offer to assist in crafting any specific tone that might be envisioned. To fully grasp the intricate workings of the analog synthesizer it helps to comprehend and visualize the signal path on its journey from input to output, and how this flow utilizes various elements of the circuitry which generate and shape sound waves.

Oscillators: Where It All Begins

Analog synthesis begins with at least one Oscillator to produce a repeating waveform, the frequency of which is determined by voltage. The most fundamental waveform any Oscillator generates is the most uniform wave possible. Made up of a single element, Sine Waves are smooth and clean, creating whistling tones.

A Voltage-Controlled Oscillator (VCO) can also introduce harmonics or other elements to offer alternative waveform shapes, each augmenting the underlying sound. Square waves generate a harsh tone heard in things like smoke alarms, Triangle waves deliver bright yet hollow timbres, and Sawtooth waves produce an unmistakable buzzing sound.

Especially useful in machines with only one Oscillator, a Sub-Oscillator duplicates and halves the frequency of its parent Oscillator and is responsible for much of the warmth found in the bottom end of analog synths. A random waveform with equal energy across all frequencies can also be generated resulting in a hissing or static sound known simply as Noise.

By varying the Control Voltage (CV) to the VCO, the frequency of the waveform alters the pitch of the tone. CV can be provided from an external source, but the standard for most modern synths was set in 1970 with the release of the Minimoog, the first commercially available synthesizer to provide proportional voltage to VCOs via a built-in piano-style keyboard.

An alternative to VCOs, DCOs (DigitallyControlled Oscillators) set frequencies by dividing down a digital timing signal usually generated by a microprocessor. Despite being digital in nature, it is not uncommon to find DCOs in analog synthesizers. VCOs produce subtle variations in frequency and waveform due to factors such as temperature, aging of components, and power supply fluctuations. This results in a slightly more organic, dynamic tone. It’s not uncommon for VCOs to have to warm up, and periodically drift out of tune. VCOs are often preferred by musicians who value more character in the sounds they produce, whereas the consistent nature of DCOs are commonly preferred by those who strive for a more precise and stable sound.

Filter Those Frequencies

Once the initial waveform is selected it is common to shape it further, usually by means of a filter. These allow certain frequencies to pass through unaltered while attenuating or cutting others completely, hence the term Subtractive Synthesis. By manipulating the frequency response of a waveform, musicians can shape the embryonic sound in unique and creative ways.

The most common type of filter found in analog synthesizers is the VCF or VoltageControlled Filter. A VCF shapes the waveform by altering the amplitude of different frequency components within the signal. There are several types of VCFs, each with unique characteristics. Of these the most common is unquestionably the Low-Pass Filter (LPF) which permits lower frequencies to pass through while cutting higher ones, helping to create a warmer, more mellow sound.