Hear something once. Play or sing it naturally, key by key, note by note, perfectly.
That would be the layman term for perfect pitch. How to know someone has it? Well with Internet now available almost everywhere in the world, it's easy to find an example of perfect pitch. Let's say a song just got released on Youtube. And then miraculously, you see a cover of the song by someone (a cover I mean dang a good, awesome, epic cover) just barely one or two days after the song has been released. That is perfect pitch.
They need no practicing. Their first try is good enough than you practicing something for weeks. Practice makes perfect just does not apply here. These people do not need music scores to play a song. They replicate the original score without having to copy from the original score.
Singing with perfect pitch is easier. The hardest part is finding the chords of the song. See a song is always made up by 2 elements. The melody and the chords. Singing is just purely melody. When a person sings with the aid of a musical instrument, he or she plays the chords of the song, while letting her voice do the melody part.
For those who don't understand a thing about music, I'll use Twinkle Twinkle little star as an example. The melody for this song - Twinkle twinkle little star, bla bla bla bla bla bla bla... THAT, is the MELODY. The chords, depends on the key you're singing in. Cmajor? Dmajor?
IF you're singing this song in C major, the chords will ROUGHLY be...
Twinkle twinkle little star, how I wonder what you are
(C) (F) (C) (G) (F) (G) (C) <- (I'm doing this roughly, without a piano XD)
If you don't have any music background, this guy will not sound like he's playing twinkle twinkle little star. But if you start singing when he starts playing, you'll notice he's actually playing something that makes a good partner with your singing! WHAT HE'S PLAYING ARE THE CHORDS!
It's not easy to catch the chords from a song. Chords are the most important part of a song. They determine the tempo, the beat, the style of the music.
Classical version by Mozart himself. This is THE ORIGINAL Twinkle Twinkle Star.
Lullaby version by ThePianoGuys.
You can have Bossa Nova version, Rock and Roll version, so on and so forth. It's not the type of musical instruments that give you the beat and feel. It is how a song is arranged into, which is determined by how the chords are played. If you play your chords fast, your song becomes a fast song. If you play your song soft, it becomes a lullaby.
So, to be able to capture a song, in it's original chords and beat, is a gift that every musician yearns to have. Arranging songs will become easier, since you can visualize your songs in different genre, then choose the one that gives off the best feel. That, is what perfect pitch is about when it comes to making music.
For amateurs, like most of us, who don't really have much chance or talent when it comes to making new music, perfect pitch allows us to capture the whole song as it is- playing a lullaby song on piano with a lullaby feel, and not a classical feel, is what perfect pitch can give.
To determine the chords of the song is difficult enough for me. For a self taught pianist, with no theory qualification, my dad says I'm good enough. But to determine the feeling of a song, is something I have yet to master. And with time running out, I know I won't have much time to spend my idle days playing the piano, seeking for ultimate self eargasm, when my working days come.
God. Please grant me perfect pitch. I don't need a girl to live together with me for the rest of my life. Just let me play and sing. Let music satire my hunger, and accompany me till the end of my days, even though I'll never have the chance to shine on stages and be etched into musical hall of fame.