If he isn't born with it, it isn't a true perfect pitch. It can be VERY close to it, but not to the point of absolute of someone who was born with it... I just entered college in music, and my teacher has perfect pitch. I'll try to learn how to develop a better perfect pitch, but it will never be "perfect". Your friend probably developed it to a point where he's never wrong, but he COULD be wrong at least once. Absolute, perfect pitchers who are born with it, can absolutely NOT be wrong.
I am sorry, Thierry, but that does not make any sense whatsoever.
Let us examine the issue, shall we?
Absolute pitch is the ability to name a tone.
But what does this ability ensues?
First you must be able to hear a certain frequency as unique. This is inborn and everyone who is “normal” (that is, who is not born deaf, for instance) will have it.
Second you must be able to remember the name given for this unique frequency. This is not inborn (how could it be) and has to be learned.
A person with perfect pitch therefore hears a frequency of 440 Hz, and remembers that this frequency goes by the name A. only the first part is inborn (hearing the frequency) the second part cannot possibly be because pitch (and their names) is conventional, cultural and has changed over the ages. For instance in Bach´s time A was tuned to 415. So a person with perfect pitch would not name a 440 hz frequency as A, and therefore would have made a mistake (as you claim to be impossible).
Mozart who was supposed to have perfect pitch would also have erroneously named a frequency of 420 Hz as A, since this was the tuning for A in his time.
Relative pitch on the other hand recognizes intervals – that is the ratio between frequencies, which means that a relative pitcher must hear at least two notes before getting his bearings – of course he won’t be able to name the note, but he will know the scale degree (even if s/he cannot name it). So someone plays C- E-G, and may think that he heard F–A-C (which is, relatively speaking, the same).
Relative pitch is fundamental and everyone is born with the potential to develop it, and just through playing will eventually get it. Perfect pitch on the other hand is far less necessary – but still a good skill to acquire. Everyone is born with the potential to develop perfect pitch, in fact one will naturally develop it by playing on a perfectly tuned instrument – like a digital piano. The main reason most people do not develop it is because an acoustic piano is never perfectly tuned – and in many cases (like in old pianos who will not hold true tuning) is tuned one semitone or one semitone below true tuning.
There are however many more issues here. For instance, the piano has each note slightly out of tune because of equal tempering. So perfect pitch for the piano is differne form perfect pitch for a singer (who must find the pitch by pure intonation). The difference may be negligible to untrained ears, but it is enough to warn singers to be not to get their bearings from a piano or they will never develop proper pure intonation. The same is true for string instruments like the violin. They must delay playing with a piano until they develop pure intonation (then they can adapt to the piano out-of tuneness).
Perfect pitch also has disadvantages. I once played on a piano apparently in tune - in fact it had just been tuned – but actually it had been tuned one semitone below. So when you pressed the C key, you would get the B sound. As a result, I was making mistake after mistake, since the sound I was getting from playing the correct keys was all wrong. And I had to stop and play a few scales to get my ears used to the tuning in order to play properly, and even that was difficult. (Incidentally, I developed perfect pitch without any concern to do so, simply by playing and practicing extensively on a digital piano). A person without perfect pitch but well developed relative pitch would not have experienced this problem.
Best wishes,
Bernhard