Rob Watts in Conversation: Unlocking the Future of Digital Audio and the Chord Quartet

In a comprehensive interview with Soundnews during its European debut, legendary digital designer Rob Watts sat down to discuss his eight-year design journey behind the revolutionary Chord Electronics Quartet upscaler, the physics of digital filters, and how digital processing can actually outperform pure analogue signal chains.

Eight Years of Research & the Blackbird WTA Structure

Developing the Quartet was, by Watts' own admission, the most difficult and demanding project of his career. Following the completion of the Hugo M Scaler, Watts embarked on an exhaustive research program to answer a fundamental question: How many filter taps are actually needed to achieve ideal transient reproduction?

• The Tap Ceiling: Mathematical modeling revealed that a traditional single-stage filter would require 4 × 10²⁸ taps (requiring a processing delay of 900 trillion years) to fully eliminate timing degradation, an engineering impossibility.
• The Blackbird Algorithm: By splitting the problem into two complementary filter structures that optimize conflicting transient behaviors, Watts created the "Blackbird WTA" structure utilized in the Quartet, reducing processing time down to mere tens of seconds while achieving unprecedented reconstruction accuracy.
• Monstrous Hardware: Packing five AMD Xilinx FPGAs (specifically the XC7S200T, compared to one in the M Scaler) and over 2,000 internal components, the Quartet generates massive computing power,boasting 3,700 DSP cores and four million filter taps.

Why Digital Can Surpass Analogue

One of the most fascinating revelations from the conversation centers on the Quartet’s inclusion of an analogue-to-digital converter (ADC), specifically designed to handle analogue sources like vinyl turntables routed through a phono stage into a DAC like the Chord DAVE:

• Eliminating Inaudible Garbage: Vinyl and high-frequency analog sources generate substantial out-of-band noise and distortion above 20 kHz. Even though humans cannot "hear" those high frequencies directly, that ultrasonic noise corrupts transient timing in the audible band.
• Transparent Decimation: The Quartet incorporates an ultra-precise 18 kHz/768 kHz decimation filter that completely strips away ultrasonic distortion. Because Watts’ advanced digital filtering is completely transparent (verified by cascading multiple filters with zero sonic loss), the resulting sound is cleaner, more stable, and more faithful than passing signals through traditional analog components.

Watts notes that this breakthrough paves the way for a radical rethink of recording studios, where future pro ADCs can bypass complex analog mixing desks and multi-capacitor signal paths in favor of transparent digital routing. With the Quartet, the boundary between digital precision and organic musicality has shifted once again.

Reference
Rob Watts in Conversation: The Designer of the Chord Quartet, Soundnews Interview