Spectral 3D Sound
Spectral 3D Sound is a real-time audio processing mode that gives any track a three-dimensional spatial quality through standard stereo headphones. It works on any track in your library — no special file format required.
Spectral 3D Sound is a Pro feature.
Enabling Spectral 3D
Tap the ≋ Audio Lines icon in the action button row on the Now Playing screen.
[SCREENSHOT: Audio Lines button — normal state vs. active state (purple)]
When active, the button glows purple. The audio character changes immediately — the stereo field opens up and instruments appear to occupy distinct positions around you.
Tap again to disable. There is a 2-second input cooldown after disabling to allow the audio engine to spin down cleanly before you can re-enable.
How It Works
Spectral 3D uses a custom audio engine that runs entirely on your device. Here’s what happens when you enable it:
The track’s audio is split into 8 frequency bands, each sent to its own isolated processing chain:
| Band | Frequency | Position in space |
|---|---|---|
| Sub-bass | 60 Hz | Below and behind |
| Bass | 170 Hz | Rear left, low |
| Low-mid | 310 Hz | Hard left |
| Mid | 600 Hz | Front left |
| Upper-mid / vocals | 1 kHz | Directly in front |
| Presence | 3 kHz | Front right |
| High | 6 kHz | Hard right |
| Air | 12 kHz | Above and in front |
Each band is processed through its own Head-Related Transfer Function (HRTF) — a mathematical model of how sound reaches your ears from that position in space. Because every band has its own isolated HRTF processor, there’s no interference between frequency ranges, which is what gives the effect its clean spatial separation.
Per-band gain compensation offsets the HRTF’s natural roll-off at low frequencies: sub-bass gets a +6 dB boost, bass +4 dB, while high frequencies receive small cuts to prevent harshness. The result is a tonally balanced image rather than a thin or hollow-sounding effect.
All 8 bands are synchronized to start at exactly the same moment using a shared hardware clock timestamp, ensuring phase-locked playback across the entire frequency spectrum from the first sample.
Head Tracking
On AirPods Pro and AirPods Max, the engine uses Apple’s built-in listener head tracking to keep the soundfield anchored in space as you move your head — the 3D image stays in place even when you turn.
On other devices and headphones, the engine reads device orientation at 60 Hz via the accelerometer and gyroscope as a fallback, rotating the soundfield in sync with how you physically hold your phone.
Sync
When Spectral 3D is active, Homecrate mutes the standard playback engine and hands audio entirely to the Spectral engine. A background sync loop checks every 2 seconds whether the Spectral engine has drifted more than 0.4 seconds from the true playback position. If drift is detected, the engine seeks automatically — you won’t hear an interruption.
Mutual Exclusivity
Spectral 3D Sound and Spatial Audio (the 🌊 Waves button, for recorded spatial mixes) cannot be active at the same time. Enabling one disables the other automatically.
The Equalizer works independently and can be combined with Spectral 3D.
Track Changes
When Spectral 3D is active and the track changes (via skip, queue advance, or Up Next), the engine receives the new file automatically and re-syncs to the new track’s playback position. You don’t need to toggle anything between tracks.
Tips
- Spectral 3D works with any locally stored audio file: FLAC, M4A, MP3, WAV, AIFF.
- It does not work with Plex streaming URLs — download the track locally first.
- The effect is most noticeable on closed-back headphones. Open-back headphones benefit too but the perceived width is subtler.
- Tracks with wide stereo mixes — orchestral recordings, electronic music, studio pop — respond better than mono or very narrow recordings.
- Battery usage increases slightly when active, as 8 parallel audio processing chains run continuously.