You can cover your eyes and see absolutely no light, but you can't cover your ears and block out all sound. Even the very best earplugs can only reduce, but never eliminate all sound. Listening seems totally automatic, but once you focus your attention on sound you'll hear a lot more.
To start, sit alone in a room, turn off all of your electronics, close your eyes, and listen to the "silence." What do you hear? Outside traffic, the ticking of a clock, the drone of the refrigerator in the kitchen on the other side of your apartment or house, or birds chirping outside? Then, listen to your breathing, it's a sound that's always there but you almost never hear it.
You can only see what's in front of you, but you hear in three dimensions. We're aware of where the sounds are coming from, in front, behind, above or below. Our ancient ancestors relied on their keen hearing to prepare to fight or flee from predators. Hearing well was a matter of life or death.
Next time there's a thunderstorm listen for the extreme dynamics, from the soft rumble of distant thunder to the jolt you get from a nearby crack of lightning, and take it all in. When you're in the city, focused listening will reveal a deep tapestry of low frequency rumble of fans, traffic, electrical hum and lighting fixtures; it's all there, underpinning the sound of everything else.
Listening to music
To become a better music listener first try and listen at super low volume levels. In a quiet room, turn down the volume on your speakers or headphones, close your eyes and listen to your favorite music. It's an exercise of sorts, focusing your attention on the music. If you mostly listen while multitasking you may be surprised when you start to notice details in the music that went unheard before.
Ideally, music should arouse feelings and emotions, and better gear is more likely to get those juices flowing. The main thing I've found with great audio systems is it's hard to stop listening to them. Even when it's late and I want to go to bed, I just have to play one more tune, or one more album. The opposite is also true, mediocre systems are easier to ignore, the music is just "on," so the music you love doesn't always draw you in and instead you talk, read, work, do anything but focus on the music. If that keeps happening it's time to consider an audio-system makeover. New speakers or headphones, or maybe an amplifier might connect the musical dots better than what you have now.
I find that really good speakers or headphones let you hear more deeply into the recordings. You can more easily focus on individual parts of the mix, the singer, and each instrument's sound is distinct. Listen to the way the bass and drums rhythms lock in, and propel the tune. Listening to the singer's phrasing and breaths, how they put more emotion into some words, and lay back on others.
Bright-sounding speakers or headphones can seem more detailed, but the sound is just brighter. Listen to live, unamplified guitars or drums not played over a club sound system, and they never sound bright or harsh, yet the detail is all there. Live music can have wide soft-to-loud dynamics, but most recorded music, in all formats, FLAC, CD, LP, whatever, have reduced (compressed) dynamic contrasts.
Headphones focus the sound between your ears but the better ones, with some recordings, can also produce sound that appears to come from outside the headphones, from further away. On the other hand, the sound from speakers is almost never heard "directly," most of what you hear from your speakers at home, or in a concert hall, is sound reflecting off the walls, floor, and ceiling in the room. Listen for that. The closer you are to the speakers, the more direct sound you hear relative to the reflections. That's why near-field listening, with the speakers 3 or 4 feet away, greatly improves stereo imaging.
Listening is mostly a matter of paying attention; the more you listen, the more you hear. The opposite is also true.
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