Show notes
For 25 years, Professor Hyunkook Lee has been researching surround sound and immersive audio. Since 2010, his focus has been on height perception—specifically, how we perceive and localize sounds coming from above. His discoveries have fundamentally changed how we approach immersive mixing. One critical finding: time differences don't work in the vertical domain the way they do in stereo. Instead, height perception relies almost entirely on spectral cues and the pitch-height effect, where higher frequencies are perceived as more elevated, regardless of speaker placement.
Emre Ramazanola brings 25 years of stereo mixing and engineering experience and has completed over 3,000 Atmos mixes—a staggering volume that gives him unique insight into what actually works in immersive mixing. Mark Gittins has been pioneering immersive audio since Apple Music launched Spatial Audio, and runs his own immersive studio, Send Sound. Together, these three experts explore the psychoacoustic principles that govern immersive audio, the limitations of current technology (particularly HRTFs and binaural delivery), and practical solutions they're using today.
You'll learn why phantom centre sounds more natural than real centre (even though it's technically more distorted), why preserving tonality is one of the biggest challenges in immersive mixing, and how APL Virtuoso—Professor Lee's binaural monitoring software—uses geometric acoustic modelling rather than impulse responses to create neutral, spatially accurate headphone monitoring. The conversation covers the 'room divergence effect' (why your brain gets confused when virtual acoustics don't match your physical room), the limitations of personal HRTFs, and exciting new immersive technologies on the horizon that could revolutionize audio delivery across all platforms.
In This Episode:
- Why height perception works completely differently from horizontal stereo localization—and what that means for immersive mixing
- The pitch-height effect: how frequency content determines perceived elevation, not panning or level
- Time vs. level differences: why time differences are 'useless' in vertical stereo (and how barn owls solve this problem)
- The fundamental problem with conventional panning tools: they colour the sound and don't provide accurate localization
- HRTFs (Head-Related Transfer Functions): what they are, why personal HRTFs don't work as well as you'd think, and the limitations of current measurement methods
- Binaural rendering and the 'cone of confusion': why you can't accurately localize sounds behind you without head movement
- Tonality vs. spatiality: why immersive engineers obsess over preserving tonal balance when delivering Atmos content
- The room divergence effect: why listening to binaural audio recorded in one room while sitting in another room causes your brain to reject it
- APL Virtuoso explained: geometric acoustic modelling vs. impulse responses, customizable presets, and why visual cues matter more than you'd think
- Mark's real-world story: mixing an Atmos song on holiday using Virtuoso and delivering it in two days (and having it translate perfectly back in the studio)
- The limits of individual HRTFs: why Emre uses Virtuoso instead, and why artists won't accept binaural mixes with tonal colouration
- Emerging technology: new immersive delivery methods beyond Atmos that remove timbre change and offer unprecedented spatial control
- Why cognition matters as much as perception: how the brain adapts to different environments, HRTFs, and how we use context clues to make sense of sound
- The future of binaural: head tracking, personalized HRTFs with virtual reality, and solving the standardization problem
About Our Guests
Professor Heung-Kuk Lee
Professor Heung-Kuk Lee is a Professor of Audio and Psychoacoustic Engineering at the University of Huddersfield and founder and director of the Applied Psychoacoustics Lab (APL). For 25 years, he has been conducting research on surround sound and immersive audio. Since 2010, his primary focus has been on understanding height perception and how to capture height information in immersive recording. He has conducted extensive psychoacoustic listening tests to determine how time and level differences work in the vertical domain and has designed microphone arrays specifically for capturing height. Based on his research findings, Professor Lee developed APL Virtuoso, a binaural monitoring tool, and other software tools used by professional mixing and mastering engineers worldwide. He is also a freelance recording engineer specializing in immersive audio.
Applied Psychoacoustics Lab (APL): apl.ac.uk | APL Virtuoso: apl.ac.uk/virtuoso
Emre Ramazanola
Emre Ramazanola is an immersive audio engineer, mixer, producer, and drummer with 25 years of experience in stereo mixing, mastering, score mixing, and production. He became interested in immersive audio before Atmos officially launched through a connection with Genelec, and was one of the first engineers able to perform stereo-to-Atmos conversions at scale. To date, he has completed over 3,000 immersive mixes—the majority of which are conversions that preserve the original artist's vision rather than full creative rebuilds. He has worked extensively with major record labels on converting new music into immersive formats and is known for his expertise in retaining tonal and artistic integrity while delivering spatial dimension. He is actively exploring emerging immersive technologies beyond Atmos and works closely with mixing engineers on standardization and delivery challenges.
Instagram: @emreramazanola
Mark Gittins
Mark Gittins is an immersive audio engineer, mixer, producer, and outside broadcast engineer with over 20 years of experience as a freelance sound engineer working across multiple formats. He has worked extensively in front-of-house mixing and owns a studio in Birmingham where he records and produces local bands. Since immersive audio launched on Apple Music approximately three to four years ago, Mark has focused on immersive mixing and founded Send Sound, his dedicated immersive audio studio. He has completed hundreds of Atmos mixes and is known for his innovative approach to immersive mixing, particularly his focus on tonality and how to overcome the limitations of current binaural delivery systems. Mark actively collaborates with other immersive engineers on emerging technologies and best practices.
Send Sound: sendsound.co.uk
About Our Host
Ashea
Ashea is a platinum-selling songwriter, music producer, and audio engineer from the UK. Her production and mixing credits include work with Alan Walker, Holy Goof, TS7, Billy Da Kid (Kiss FM), Steve Smart (Kiss FM), The Wideboys, MER, Sony Music, 2Tone Records, BBC, and SVT1 (Sweden). Through the Production Expert Podcast, she brings together world-class audio professionals, researchers, and innovators to explore the science, craft, and philosophy of recording, mixing, and the future of immersive audio.
Website: asheamusicofficial.com
Key Resources & Links
- Applied Psychoacoustics Lab (APL): apl.ac.uk
- APL Virtuoso (Binaural Monitoring Software): apl.ac.uk/virtuoso
- Send Sound (Immersive Studio): sendsound.co.uk
- University of Huddersfield - Audio & Music Technology: hud.ac.uk
- Dolby Atmos for Music: dolby.com
- Genelec UNIO Monitoring: genelec.com/unio
- Apple Spatial Audio: apple.com/music/spatial-audio
- ITUR 1116 (Critical Listening Room Standards): itu.int
- Aura 3D Format: auralync.com
- Source Nexus Suite: sourceelements.com
- RSPE Audio Solutions: rspeaudio.com
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