Direct answer
An iPhone equalizer app can shape audio it is allowed to process. ToneEQ applies software EQ to compatible audio played by its own engine; iOS does not expose a public API that lets a third-party app equalize every other app system-wide.
How it works
An equalizer changes the level of selected frequency ranges. A graphic EQ presents fixed bands; a parametric EQ also lets you choose frequency, gain and bandwidth.
ToneEQ decodes compatible local files in its own audio engine, applies the selected device and preference layers, compensates preamp when needed, then sends the result to the active output.
Device-aware profiles help the same preference follow different compatible headphones without pretending that every headphone needs the same correction.
When to use it
- Use a gentle device correction as a baseline, then make small preference changes.
- Compare with bypass at a similar loudness; louder often sounds better even when the curve is not better.
- Leave headroom when boosting several bands, especially in bass-heavy material.
Limits to know
- ToneEQ cannot insert itself into system audio from streaming, video, game or social apps.
- Bluetooth codec, device DSP, volume normalization and hardware tuning can still affect what you hear.
- EQ is not a hearing test or medical treatment.
Frequently asked questions
Can iOS apps provide system-wide EQ?+
Not through a public third-party audio-processing API. Apps can process audio they play or use platform-specific controls where Apple provides them.
Does the built-in Music EQ work the same way?+
Apple’s own Music settings are platform features. ToneEQ uses its own engine for compatible local audio and clearly reports when software EQ is unavailable.