FiDef® – Psychoacoustic Enhancement by FideliQuestFiDef® by FideliQuest is a very low-amplitude psychoacoustic stimulus designed specifically for audio engineers. Its purpose is to help the listener’s brain relax, focus, and engage more deeply with incoming audio. Laboratory testing using functional neuroimaging has shown that FiDef increases brain activity related to perception and attention, enhancing the subjective experience of listening.
Originally developed in the United States by FideliQuest LLC, FiDef was first introduced within MAAT’s thEQblue plugin and is now available as a standalone processor for all major formats, including VST 2, VST 3, AAX Native, and Audio Units. It is a patented 64-bit process that takes a fundamentally different approach compared to traditional DSP tools, relying on auditory neuroscience rather than direct signal manipulation.
Since the earliest days of recorded sound, the goal of audio technology has been to recreate a lifelike listening experience. While digital formats solved many limitations of analog systems, they also introduced a subtle sense of detachment. Even modern high-resolution formats often fail to fully reproduce emotional immediacy. FiDef addresses this by improving the listener’s connection to the audio, regardless of format, compression, or playback system.
At its core, FiDef works by generating a sub-audible, broadband, anharmonic signal that is dynamically correlated with the source material. Unlike dither, it does not modify or degrade the original audio but is instead added alongside it. This signal is carefully shaped to stimulate the auditory system directly, bypassing conscious analytical processing and reducing the effort required by the brain to interpret sound. The result is increased perceived detail, clarity, and emotional engagement.

Key Concepts

• Sub-audible, broadband, anharmonic signal
• Dynamically correlated with source audio
• Does not alter the original signal
• Bypasses conscious listening processes
• Reduces cognitive load while increasing perceived detail

Sonic Benefits

• Improved definition and clarity
• Increased detail and nuance
• Better speech intelligibility
• Enhanced soundstage width and depth
• Stronger emotional engagement
• More natural and immersive listening experience

What Makes FiDef Different

• Not EQ, compression, or dynamics processing
• Not analog modeling or simulation
• Not dithering or noise reduction
• Not modulation, distortion, or resynthesis
• Not time or frequency domain manipulation
• A unique psychoacoustic augmentation layer

Applications

• Mixing: improved separation and focus of elements
• Mastering: enhanced overall cohesion and engagement
• Broadcast & Post: better clarity and listener attention
• Games: increased immersion and spatial perception
• Forensics: improved intelligibility of complex material
• Sound Design: spotlighting specific sonic elements
• Restoration: expanded perceived spatiality

Profiles

• TRUCKN: subtle overall enhancement (default)
• TRUCKN HUSH: lower intensity for dynamic material
• SUTRO: emphasizes high frequencies and spatial width
• RESNO: focuses on upper mids and texture
• EVOSE: warmer, more forward and energetic sound

Important Notes

• Works subconsciously; effects may not be obvious analytically
• Over-focused listening can reduce perceived impact
• Casual listening reveals stronger results
• Listeners often notice improved engagement without knowing why

Technical Highlights

• Patented 64-bit processing
• Adds signal without changing loudness or frequency balance
• Works on compressed and high-resolution audio alike
• No workflow or delivery changes required

System Requirements

• macOS 10.9 or newer (64-bit, Universal Binary 2)
• Windows 7 or newer (32 & 64-bit)
• Plugin formats: AAX Native, AU, VST 2, VST 3
• Sample rates: 44.1 – 384 kHz
• FiDef processing: 44.1 – 192 kHz

Summary

FiDef represents a new category of audio processing focused on perception rather than signal alteration. By leveraging psychoacoustic principles and brain response, it enhances how audio is experienced rather than how it is measured, resulting in deeper, more engaging listening across all playback systems.