DCOs, or Digitally Controlled Oscillators, were a major milestone in synthesis technology.
They paved the way for the groundbreaking synthesizers that defined the sound of the 80s in music.
But the term might sound confusing if you haven’t heard it before. Are DCOs analog, or digital? Why are they so common in synths from the 80s and how do they contribute to the memorable sound of the era?
If you’re looking to capture authentic vintage synth sounds from the 80s and beyond, it’s important to understand what DCOs are and the role they played in the development of music technology.
In this article, I’ll break down everything you need to know about DCOs and how they contribute to the sound of your favorite synths of the analog era.
Let’s get started.
What is a DCO?
A DCO is a synthesizer oscillator that functions as a basic building block for subtractive synthesis in hardware instruments.
The term DCO stands for ‘digitally controlled oscillator,’ in reference to the earlier VCO, or ‘voltage controlled oscillator.’
Just like a traditional synth oscillator, the sound generated by a DCO remains completely analog. The only digital element is the control signal used to keep the oscillator’s frequency consistent.
Since early VCO designs had persistent issues with tuning stability, the arrival of DCO technology enabled new possibilities in synth design.
DCOs are notable for ushering in a new generation of synths in the 1980s, including classics like the Roland Juno series, the Korg Poly61, the Oberheim Matrix 6 and many others.
In addition to these beloved 80s synths, DCOs can be found in modern synths such as the Dave Smith/Sequential Prophet ‘08.
Why use digitally controlled oscillators?
With the definitions out of the way, what are the core differences between DCOs and their predecessors, and why did DCOs replace VCOs in the 1980s?
The answer lies in the progression of synth technology toward modern polyphonic analog synthesizers.
The first synthesizers were massive modular systems, far larger than today’s Eurorack setups.
These systems included the familiar elements we’d recognize today, but they weren’t patched by default in a standard configuration.
The common prepatched signal chain of an oscillator followed by a filter and envelope-controlled amplifier wouldn’t emerge until the mid-70s.
But even then after the basic signal flow became fixed, portable instruments of this era still had a problem.
Their oscillators would fluctuate in pitch depending on temperature, transport conditions and how long they had been powered on. This presented major issues for touring artists that wanted to bring synthesizers on the road.
With the advent of digital technology in the early 80s, clever engineers were able to solve the tuning issue without completely redesigning the oscillators that provided the core sound of their synths.
This meant roadworthy polyphonic instruments could finally be produced for a price gigging musicians could afford, leading to the explosion of DCO-based synths I mentioned above.
DCOs vs. VCOs
Though DCOs proved an effective solution to the tuning stability problems of the late 70s, modern components can produce pure analog VCOs that hold their tuning well.
While they’re typically more expensive than DCOs or other oscillator designs, some vintage purists prefer synths with fully analog topology.
And though the sonic differences between the two are subtle, DCOs have their own vintage pedigree that lovers of 80s-style synth sounds will recognize.
But if you’re still confused, here’s a basic breakdown of the differences between VCOs and DCOs.
VCO:
Fully analog, including rate clocking
Found on older vintage synths and modern boutique analog synths
Older designs can suffer from pitch fluctuation and tuning issues
Costlier to implement effectively
DCO:
Analog signal, digital control
Found on synths from the 80s to today
Very good pitch stability
Can be produced cheaply, so often used for feature-rich polysynths and prosumer analog gear
How do DCOs work?
So if the signal generated by the DCO is still analog, where does the digital part come in?
Analog oscillators can be a bit hard to understand if you don’t have a background in electronics.
But the basic mechanism is that a capacitor gets charged up, discharged and charged up again in a predictable pattern.
The changes in voltage over time create a periodic wave that we hear as an audio signal when it gets amplified by a VCA.
In this model, a slow increase in the capacitor’s charge creates a rising initial phase of the waveform, followed by an abrupt drop when the voltage is reset before rising again.
This creates a waveform sometimes called a ‘ramp’ but more commonly known as a sawtooth wave.
The oscillator tuning problem arises from the analog circuit that tells the capacitor when to discharge and restart the ramp.
Even minor inconsistencies in the timing of the discharge can lead to fluctuations in the frequency of the oscillator’s output signal.
DCOs work by digitizing the reset pulse used to trigger the capacitor to discharge inside the oscillator circuit.
The result is a fully analog audio signal that’s kept in tune by the unwavering digital control pulse.
How to get authentic DCO-style sound in your DAW
With so many vintage instruments that depend on DCOs, you might be wondering what it takes to get their authentic sound in your DAW.
Luckily, emulating DCOs in software can be very convincing if you choose the right plugin.
We built our BA-1 synth to give you the best of the 80s in synthesis, right at your fingertips.
From accurate vintage-modeled oscillators to a juicy resonant filter, BA-1 is a simple yet powerful synth plugin with plenty of retro character.
Watch Alex break down the key features of BA-1 and demonstrate its capability for 80s-style synth magic:
While the initial design took inspiration from a DCO-based portable synth from the 80s, we went way beyond the original’s capabilities to make it an ideal analog-style synth for the modern producer.
Digital oscillator control
Most synth enthusiasts agree that analog oscillators offer something special.
But DCOs are one of the best examples of analog and digital working together to enhance the properties of both technologies.
When it comes to subtractive synthesis, your starting waveform is like the marble from which you’ll sculpt your masterpiece.
It’s worth it to start with the right material!
Now that you know the basics of DCOs, you’ll have a solid foundation for how they affect the most important factors in synthesis and sound design.