Hi!
I thought I'd post something too (after a few years =)
Truth is, you can learn it...
..but it is not "perfect pitch" by definition. Perfect pitch basically is something that some people seem to have by nature. About 10 percent of all musicians do have perfect pitch. Normally, when someone with PP hears a note, he/she also "sees" it in a specific color thus being able to determine what note it is. Not all of them are 100% accurate though. Some can determine a note with an accuracy of only a few cents while others are not as accurate and can only distinguish halftones.
Science does not definitely know whether or not is is a genetical thing. It seems, that the amount of those with PP varies from culture to culture. Members of tonal-languages are more likely to develope PP than those of non-tonal languages. In asia, for example, about half of all music students seem to have PP. It might depend on their hearing habits, because mandarin-chineese, for example, is a language that depends a lot on pitch variations.
As for someone without PP: You can learn something that is called "relative pitch". That is the ability, to determine intervals based on a root note. You can go as far as memorizing one reference note - say A 440 Hz. With enough practice you can memorize that tone well enough, that it works like a tuning-fork in your head. That means you hear a note that someone plays, then you 'activate' your reference A in your head and then you can tell the interval, thus determining what note has been played.
Of course this takes a lot of practice, but it definitely can get you very close to PP.
Btw - having perfect pitch is not a blessing by default nor is it something that one needs in order to be a successful musician. Actually a lot of people with PP find it rather unpleasant when playing transposed music because the written notes do not correspond to their hearing habit. I have also talked to some guys with PP who say that they cannot listen to a piece of music without analyzing every bit of it and hearing everything that is slightly out of tune as "wrong". So perhaps one should be happy without PP.
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