Wave Digital Filters with Kurt Werner (Soundtoys, ex-Native Instruments, ex-iZotope) | WolfTalk #030

Learn the secrets of RX, Ozone, Neoverb, Vinyl, and more!

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Introduction

Kurt James Werner, PhD, is a senior research scientist at Soundtoys and one of my favorite researchers in audio DSP (virtual analog modeling in particular).

While you may not have read his papers, it’s very likely that you used one of the plugins he worked on:

Neoverb
Vinyl
RX
Guitar Rig (Hammond vibrato/chorus)
Ozone
Neutron
Trash

If you start peeking into the research of modeling analog audio effects in plugins, you stumble across his name right away.

I consider him not only brilliant, but also insanely productive. Definitely a role model for me!

In the research world, he’s mostly known for his work on Wave Digital Filters (WDFs). It’s a technique for creating a mathematical model of an analog circuit that once done is easy to implement (provided you use a WDF library).

WDFs are great for modeling analog audio effects to put them inside plugins.

But as a true researcher, Kurt is involved many other audio subfields that we discuss in the podcast!

Did I mention that he’s a graduate from Stanford’s CCRMA?

In this episode, you’ll learn about Kurt’s transition from academia to industry, his work on products at iZotope, Native Instruments, and Soundtoys, and the realities of being a research scientist in an audio plugin company.

You’ll also learn all about WDFs, which is a powerful tool to master.

Trust me, you don’t want to miss this one 😉

Note: If you like the podcast so far, please go to Apple Podcasts and leave me a review there. You can do so on Spotify as well. It will benefit both sides: more reviews mean a broader reach on Apple Podcasts, and feedback can help me to improve the show and deliver better-quality content to you. You can also subscribe and give a like on YouTube. Thank you for doing this 🙏

Episode Contents

From this episode, you will learn:

How Kurt’s early musical and DIY electronics experiments led him toward audio DSP
How was it like to study at CCRMA under Julius Smith, Jonathan Abel, and Ge Wang
A clear, high-level explanation of Wave Digital Filters, their origins, and why they matter in virtual analog modeling
Insights from his work at iZotope
His current work at Soundtoys
Creative music practices like circuit bending and 1-bit music
Whether you need a PhD to work at an audio plugin company
How audio research translates into plugins

Tips & Advice

A DSP algorithm’s performance is not determined by counting adds and multiplies (as often done in research papers); you need a proper benchmark
Getting a research position in the audio industry requires demonstarting research ability through
1. a PhD (or a very good Master’s thesis),
2. written papers
3. published papers
A PhD is not required for DSP engineering roles; for these, practical C++ experience is often more valuable
To write good papers, you need to read a lot of other papers, understand them, and critically analyze them; “You need to read all the papers” 😉
In your WDF models, consider that the circuit must warm up before proper audio samples processing can start; slamming a battery (even a virtual one) into a circuit will always produce a sharp transient!
Attending conferences like DAFX is important not only for being up-to-date with the latest research, but also for career prospects

This episode was recorded on February 25, 2025.

References

People

Kurt Werner

Academia & Research

Industry and Creative Figures

Educational & Research Institutes

Companies & Products

Hardware & Gear

Classic audio hardware

Roland TR-808
Roland TR-505
Casio SK-1
Altec 9062A (Graphic EQ)
RCA Mark II
E-mu SP-1200
Tascam Digital Four-Track Recorder
Atari Punk Console

Retro platforms

Software, Frameworks & Tools

WDF libraries

Books

Academic Papers & Theses

Werner, K. J. (2016). Virtual analog modeling of audio circuitry using wave digital filters (Doctoral dissertation, Stanford University). [PDF] stanford.edu
Werner, K. J., & Burtlington, V. T. (2024). Graphic equalizers based on limited action networks. [PDF] dafx.de
Werner, K. J., Abel, J., & Smith, J. (2014, September). A physically-informed, circuit-bendable, digital model of the Roland TR-808 bass drum circuit. [PDF] qub.ac.uk
Werner, K. J. (2019). Generalizations of velvet noise and their use in 1-bit music. [PDF] dafx.de
Fettweis, A. (1986), Wave Digital Filters: Theory and Practice [PDF] CCRMA
Franken, D., Ochs, J., & Ochs, K. (2005). Generation of wave digital structures for networks containing multiport elements. [[PDF] IEEE Xplore]](https://doi.org/10.1109/TCSI.2004.843056)