What's a good iOS app for fine-tuning the sound of music playing from my iPhone?

EQU: Music Equalizer - Amplify is a solid choice when you want to take control of your iPhone's audio output. It provides a user-friendly interface to adjust various frequency bands, allowing you to boost the bass, enhance the vocals, or tweak the overall sound to match your headphones or personal preferences. You can create and save custom EQ presets for different music genres or listening environments. The app also includes a system-wide equalizer, which means the audio adjustments apply to all apps on your device, not just music players. This is particularly useful if you find that certain apps have poor default audio settings. With its intuitive design and powerful features, EQU: Music Equalizer - Amplify gives you the tools to sculpt your sound exactly how you want it.