I’ve been playing around a lot recently with the UDO synths, and have a Summit I’m about to dig into. It’s something I’ve wanted to have a play with for a while, ever since using a friend’s Peak. In particular, after uploading demos of the Super 8 there were a fair few comments relating to the Summit, and how if delivered so much more for a lot less cash. Novation’s oscillators are called Oxford Oscillators, and UDO refers to its as DDS oscillators, but essentially they all use FPGA technology.

So, while doing some prep I researched info about FPGA monitors, and thought it may be of interest to others.

What is an FPGA?

An FPGA (Field-Programmable Gate Array) is a reconfigurable digital processor capable of running multiple parallel processes at extremely high speeds. Unlike a DCO, an FPGA can generate oscillators entirely in the digital domain while maintaining ultra-fast performance.

FPGA Oscillators in FM Synthesis

• FPGA-based oscillators can process frequency modulation at extremely high speeds, allowing for clean, artifact-free audio-rate FM.

• Because they operate digitally, they provide precise control over waveform shaping, phase modulation, and harmonic content.

• Multiple oscillators can run in parallel with minimal latency, enabling complex FM synthesis with high modulation depth and clarity.

Speed and Precision

One of the key benefits of FPGA oscillators is their incredible speed, often operating at speeds far beyond traditional digital signal processors (DSPs) or microcontrollers. The exact speed depends on the FPGA hardware and implementation, but they can typically run at:

• Sample rates of 24 MHz to 100+ MHz (compared to standard audio DSP rates of 44.1 kHz or 96 kHz).

• Clock speeds in the hundreds of megahertz to gigahertz range, allowing for ultra-high precision waveform generation.

• Latency as low as microseconds or even nanoseconds, making them perfect for real-time modulation.

Unlike general-purpose processors or microcontrollers, which execute instructions sequentially, FPGAs process multiple operations in parallel. This allows FPGA-based oscillators to generate waveforms with ultra-low latency and high precision, ensuring stable and consistent sound quality.

Why Does Speed Matter?

1. Audio-Rate FM and Modulation

   • For FM synthesis, the modulator oscillator needs to be as fast as (or faster than) the audio signal it's modulating.

   • Traditional DSPs often struggle with high-frequency modulation due to computational limits, introducing aliasing and artifacts.

   • FPGA oscillators can handle FM at ultrasonic speeds (above 20 kHz), ensuring clean and complex timbres.

2. High-Resolution Waveforms

   • Because of their speed, FPGA oscillators can generate ultra-high-resolution anti-aliased waveforms without relying on interpolation tricks.

   • This results in smooth transitions between waveform shapes and more natural harmonic evolution.

3. Parallel Processing for Multiple Oscillators

   • Unlike DSP chips that execute tasks sequentially, FPGAs process multiple oscillators in parallel, allowing for complex layering, unison, and polyphony with minimal computational strain.

Audio-Rate Frequency Modulation (FM)

The speed of an oscillator is crucial for audio-rate frequency modulation (FM), a synthesis technique that creates rich harmonic content by modulating one oscillator with another at audible frequencies. Traditional digital oscillators can struggle with the rapid calculations required for high-speed FM, leading to aliasing and unwanted artifacts. FPGAs, however, can handle these computations effortlessly, enabling clean and precise modulation. This results in complex, evolving timbres that would be difficult to achieve with slower processing methods.

FPGA oscillators are not only fast but also highly stable. Unlike analog oscillators, which can drift due to temperature fluctuations, FPGA-based oscillators remain consistent over time. Additionally, they can be reprogrammed via firmware updates, allowing for new waveform designs and synthesis techniques to be implemented without changing hardware.

Digitally Controlled Oscillator (DCO) vs FPGA for FM Synthesis

I only realised that FM synthesis wasn’t possible using DCOs when I bought a Prophet 08 many years ago, it has audio rate modulation of the filter, but not of the oscillators. This was due to the oscillators on the Prophet08 and Rev2 being DCO, not VCO. It is obvious to me that digital oscillators will have difficulties with FM due to processing speeds, but I wanted to understand why FPGA was a better option.

When considering FM synthesis, the difference between a Digitally Controlled Oscillator (DCO) and an FPGA-based oscillator comes down to speed, flexibility, and processing power.

A DCO is a type of oscillator that generates waveforms using analog circuitry but is digitally controlled for tuning stability. Unlike a fully digital oscillator, a DCO still relies on analog waveform generation but avoids drift by using a digital clock for frequency control.

DCOs in FM Synthesis:

• Since the waveform generation is analog, DCOs are not well-suited for complex FM synthesis.

• They generally lack the high-speed modulation capabilities needed for audio-rate FM (where a modulator oscillator influences the frequency of another at rates within the audible spectrum).

• The response time of a DCO may introduce limitations in modulation depth and accuracy.

For standard subtractive synthesis, a DCO provides analog warmth with digital stability. However, for FM synthesis, an FPGA-based oscillator is vastly superior due to its ability to handle fast, complex frequency modulations with high precision and stability. If you're looking for rich FM tones with detailed harmonic structures, an FPGA is the better choice.

Can an FPGA Oscillator Sound Like a VCO?

Yes, an FPGA-based oscillator can sound like a VCO (Voltage-Controlled Oscillator), but achieving true analog behavior requires careful design and processing. While an FPGA is inherently digital, its high-speed, high-resolution capabilities allow it to closely model the characteristics of an analog VCO when implemented correctly.

How FPGA Oscillators Can Emulate VCOs

✅ High Sample Rate & Resolution

• Analog VCOs produce continuous waveforms, while digital oscillators generate discrete samples.

• FPGA oscillators can run at extremely high internal sample rates (MHz range), reducing digital artifacts and making them behave more like analog waveforms.

✅ Anti-Aliasing & Oversampling

• One of the biggest giveaways of digital oscillators is aliasing, which can introduce unnatural high-frequency artifacts.

• FPGA oscillators can oversample heavily (well beyond standard DSP rates) and apply high-quality filtering, mimicking the smooth, natural tone of a VCO.

✅ Analog Imperfections & Drift

• Real VCOs exhibit subtle pitch drift, phase noise, and waveform inconsistencies due to temperature changes and circuit tolerances.

• FPGA oscillators can introduce controlled "analog-style" drift, instability, and slight non-linearity to simulate this behavior.

• Some synths (like the UDO Super 6) model VCO imperfections digitally within an FPGA to achieve an organic, warm sound.

✅ Warmth Through Analog Filtering

• Many FPGA-based synths, such as the Novation Peak/Summit and Waldorf Quantum, pair FPGA oscillators with real analog filters to add warmth and remove any remaining digital harshness.

• This hybrid approach delivers the best of both worlds—the precision and flexibility of digital with the character of analog.

Can an FPGA Oscillator Fully Replace a VCO?

Almost, In a mix, a well-designed FPGA oscillator with analog processing can sound nearly indistinguishable from a real VCO. However, pure analog VCOs still have natural, unpredictable nuances that digital models can struggle to fully replicate. The hybrid approaches, as taken by UDO and Novation, pairs FPGA oscillators with analog filters and/or analog VCAs to offer a convincing balance between VCO realism and modern flexibility.

Bottom Line: A high-quality FPGA oscillator can sound just like a VCO, especially with the right design choices. Many modern hybrid synths use FPGAs to create analog-style oscillators with added digital flexibility. I doubt in a blind test anyone could tell the difference confidently enough to bet their synths on the result!

Synths That Use FPGA Oscillators

Several high-end and innovative synthesizers use FPGA-based oscillators to achieve high-speed, high-fidelity digital synthesis. Here are some notable examples:

1. UDO Super 6

• A binaural hybrid synthesizer that utilizes FPGA-based oscillators for super-fast digital waveform generationwhile keeping an analog signal path for warmth.

• Features audio-rate modulation, including FM and phase modulation, with minimal aliasing.

2. Waldorf Quantum & Iridium

• Waldorf’s flagship digital/hybrid synthesizers use FPGA-generated oscillators to handle wavetable, granular, and FM synthesis at ultra-high precision.

• The fast processing speed of the FPGA allows for smooth morphing wavetables and complex FM synthesiswith minimal artifacts.

3. ASM Hydrasynth

• Uses an FPGA-based digital engine for its wave morphing oscillators and advanced synthesis capabilities.

• Capable of high-speed waveform transformations, FM synthesis, and deep modulation routing with extreme precision.

4. Modal Electronics 002

• Features FPGA-driven oscillators for numerically controlled waveforms, allowing for ultra-stable, high-resolution digital synthesis.

• Provides high-speed modulation, including FM, without the limitations of traditional DSP-based synths.

5. Novation Peak & Summit

• Use FPGA-based "Oxford Oscillators" for ultra-high resolution, anti-aliased digital waveforms.

• The speed of FPGA processing allows for high-quality FM, phase modulation, and wavetable synthesis, offering analog warmth combined with digital precision.

Novation’s Oxford Oscillators

Oxford Oscillators are a type of high-resolution digital oscillator developed by Chris Huggett (of OSCar and Bass Station fame) for Novation’s Peak and Summit synthesizers. These oscillators leverage FPGA (Field-Programmable Gate Array) technology to generate waveforms with extreme precision and flexibility. The Oxford Oscillator therefore has the same characteristics as FPGAs

Anti-Aliased Waveform Generation

Aliasing is a common problem in digital oscillators when high-frequency components fold back into the audible range, creating unwanted noise. Oxford Oscillators use FPGA power to generate mathematically perfect, alias-free waveforms—even at extreme modulation rates.

Analog-Style Sound with Digital Flexibility

• Unlike basic wavetable synthesis, Oxford Oscillators dynamically shape waveforms in real-time, rather than relying on pre-recorded tables.

• They model classic analog oscillator behavior while maintaining digital stability (no tuning drift, perfect consistency).

• They are paired with analog filters and VCAs in Novation’s Peak and Summit, giving a hybrid balance of warmth and precision.

Advanced Modulation Capabilities

• Audio-rate FM and Ring Modulation: The speed of the FPGA allows these oscillators to modulate each other at high frequencies, creating rich harmonic content and evolving timbres.

• Wave Morphing and Shaping: Unlike fixed digital waveforms, Oxford Oscillators can smoothly morph between different shapes, expanding sound design possibilities.

In summary, by combining FPGA technology with flexible wave-shaping and analog filters, Oxford Oscillators deliver the best of both analog and digital worlds, making them a standout feature in Novation’s Peak and Summit synthesizers.

✅ Ultra-clean, high-resolution digital waveforms
✅ Low aliasing and high-speed processing
✅ Capable of complex FM synthesis and modulation
✅ Hybrid approach with analog filters for warmth

Conclusion

FPGA oscillators are orders of magnitude faster than traditional digital oscillators found in DSP-based synthesizers. Their high speed allows for audio-rate frequency modulation, precise waveform generation, and ultra-low latency, making them a great choice for modern digital and hybrid synthesizers.