An equalizer (EQ) works much like the treble and bass controls on a stereo, but with even more power and flexibility.
You can use the iTunes equalizer to fine-tune specific frequencies of the sound spectrum. By adjusting frequencies, you can customize your music for different genres, listening environments (different rooms in your home, for example), and output methods (such as speakers or headphones). You can adjust equalizer settings manually or choose from more than 20 presets of the most commonly used EQ settings.
To open the iTunes equalizer:
Choose View > Show Equalizer.
The horizontal values across the bottom represent the spectrum of human hearing in hertz (Hz). The lower frequencies (starting with 32 Hz) are bass frequencies and the higher frequencies are treble.
The vertical values on each bar represent decibels (dB), units that measure the volume or intensity of each Hz frequency. By moving the sliders (also called “fadersâ€) up or down, you increase or decrease the sounds that you hear in that frequency range.
“Preamp†is a secondary volume adjustment applied to all frequencies equally. You might want to increase or decrease the preamp volume when listening to music that was recorded particularly quietly or loudly.