Lately a few musician friends discussed transposition in relation to perfect pitch (absolute pitch) and relative pitch. Some say musicians with perfect pitch have more trouble transposing than those with only relative pitch.
Here I share some of my takes, particular on some of common myths. Here's my disclaimer though: my empirical experiences may or may not match with some cognitive models, let alone what's really going on in the brains. However, I am confident enough to say, what I summarize here has been proved practical by myself and many of my fellow musicians.
I recommend reading Wikipedia on the pitch topic for better understanding of the topic and the its various issues. Here I merely provide some of my personal experiences.
The most commonly debated topic on perfect pitch is whether it's natural or nurtured, i.e. can one learn to have perfect pitch or does one have to be born with it?
Most of my Taiwanese musician friends have perfect pitch and most of my non-Asian musician friends don't. Some studies suggest the acquisition of tonal languages may help cultivate perfect pitch. Many commercial training programs (search "Perfect Pitch Training") have successful stories to help people acquire perfect pitch.
I don't have perfect pitch, but during the days when I practice string instruments regularly, I did attain less-than-perfect pitch: I was able to quickly recognize and produce the tones on two of the empty strings without any reference. I had to recognize or produce other pitches by cheating with relative pitch, though. Now that I don't practice string instruments as much, I seem to have lost it. I do believe perfect pitch can be learned. And with that notion, I also believe there are different degrees of "perfection". Some of my friends' pitch sense is dead on; others are within a quarter tone. Some cheat with the help of relative pitch (but much faster than I was); some can only recognize certain instruments (i.e. cheat with tone color).
With perfect pitch or not, I have never noticed any difference in their musical achievement.
There are a few occasions when I wish I had perfect pitch though: when a tuner is not handy; music with only instruments with adjustable pitches (keyed or valved wind instruments are better; pre-tuned empty strings help anchor the pitch center when those strings are played; trombone's first position is usually an absolute point; vocal is the most challenging, though); joining an improvised performance in the middle of a piece with a lot of fast modulations. However, these are all technical inconveniences that can be easily addressed.
Yes, there are some situations when my lack of perfect pitch does affect my listening experience. For example, when listening to modern pieces which tonal center is either constantly shifting or non-existing; complex chordal structures (pieces involving more than 2 keys simultaneously); crowded clusters; etc. These pieces usually require many listenings before I can transcribe correctly. Some of my friends are amazing transcribers and most of them have perfect pitch.
Few people would reject the fact that relative pitch can be learned via ear training. Actually, I have never met a real "tone-deaf" although many of my non-tonal language speakers claim they are. Almost all people learn to distinguish pitches after being shown how to really listen to tones. Again, there are different degrees of the ability in terms of recognizing and producing relative pitches. Most people are familiar with intervals on a major or minor scale, but less familiar with altered intervals; most people can recognize a chord with 4 different notes reliably, but not beyond. However, it's just a matter of training. Among the musicians I know, those who put in enough time are able to develop decent relative pitch ability.
Transposition means moving music from one key to another. Some argue that musicians with perfect pitch have harder time transposing because their pitch senses are fixed so moving notes around will drive them nuts. I personally have never actually met anybody who cannot transpose because of their perfect pitch, although they may use different method to do transposition.
The most common situation that requires transposition is singing. When a note is out of our vocal range, we move the melody up or down so we can sing it. Almost all people I know, with perfect pitch or not, have no problem doing so.
Another common application of transposition is when accompanying a vocalist. Pianists, guitarists, and bassists are required to do this a lot. Besides using automatic transposition devices (transposition button on electronic keyboards or a capo on guitar neck), those who master the skill, regardless their perfect pitch sense or lack thereof, have good understanding of scales and chord progression, and of course, good skills on their own instruments.
(On a side note, I envy musicians with perfect pitch who can just start accompanying the singer by listening. I usually need to guess the first note, which then can become either the target note or a passing note, depending on whether I guess right or not.)
Now, when transposition involves sight-reading in one key and playing in another, things get a little bit more complicated. Common scenarios include:
* Playing or conducting scores that involve transposed instruments (for example, if the French horn part has an E, the trumpet part has a D, the trombone part has an F, and Bariton saxophone has a C, the conductor would need to recognize it's (probably a 3rd inversion of) an F dominant 7th chord).
* Playing parts of other instruments. For example, the viola player (C instrument written in alto clef) may be asked to play a French horn part (F transposed instrument written in treble clef). Or a clarinet player (Bb instrument written in treble clef) is asked to play the alto flute part (G instrument written in treble clef).
* Sight-reading music written in one key and playing in another. For example, reading a piece written in F minor but playing in B minor.
* Combination of the above. For example, playing the whole orchestrated piece on piano in a different key. Or say, a piece is written to sound in concert key F major, but now the clarinet player is told to play the alto flute part and sound in the key of B major, i.e. the clarinet player needs to figure out the interval between the target concert notes F and B, and the given instrumental interval differences between clarinet (Bb) and alto flute (G).
* In jazz or commercial music, the ability to transpose also includes reading and transposing chord symbols on the fly, along with the written melody lines. This adds yet another layer of complexity.
There are three common methods that I know are used.
1. Move notes up/down a certain interval in mind. For example, in the concert key of G major, when the viola player sees a note in the French horn part residing on the first line in a treble clef (E in French horn part, or concert A), the viola player would move the note up to the second line (A in alto clef). In the same manner, the viola player will move every note in the French horn part a third up. Note that the French horn part has the key signature D and the target viola part will have key signature G so if there is a natural F (the 1st space in treble clef, concert Bb) in the French horn part, after moving a 3rd up to the 2nd space in alto clef, the note needs a flat accidental.
2. Clef transposition. Imagine a different clef for the part to transpose the music. There are 7 different clefs that can make any note become any other note in the scale: treble, soprano, mezzo-soprano, alto, tenor, baritone, and bass (historically there are other clefs but they are equivalent to or octaves apart from some of the 7 above). For example, if a tenor trombonist (concert pitch written in bass clef) needs to play a baritone saxophone part (Eb written in treble), the trombonist only needs to imagine a bass clef in front of the baritone saxophone part, with a key signature of one more flat, because a note on the 1st line of the baritone saxophone's treble clef part is E, or a concert G, and the same 1st line in bass clef is also G. Of course, depending on the situation, shifting octave will sometimes be called for.
3. Read the notes in terms of harmonic and scalar relation and then execute it in the new key. For example, if I see D, F#, C in the key of G, I understand this is the 1st, 3rd, and 7th of the dominant chord of the key. If I am to play it in the key of Db, I will play the 1st, 3rd, and 7th of the dominant chord of the key (Ab7: Ab, C, Gb). The same technique is also used to transpose chord symbols. Instead of using cumbersome theoretical names (tonic, super-tonic, mediant, subdominant, dominant, submediant, subtonic (or leading tone)), Roman letters are commonly used. Some even go further to assign syllables to notes for singing (movable Do solfège).
All these methods work. I personally find the first method very tiring but a lot of musicians use them because they don't need to transpose a lot and the method is very easy to learn. An outstanding trombonist with perfect pitch told me that her sense of pitches and the note position in the staff are so tightly connected that moving notes around is too confusing for her; thus she uses clef transposition. Many jazz pianists I know use the third method.
A side note on solfège: scalar solfège is commonly used to do transposition. However, I know few people who really do chromatic solfège. Most people have no trouble learning it but the syllables turn out to be merely lyric to them during transposition. I don't think this proves anything since these people have achieved good listening skills before they learn chromatic solfège. Perhaps the lack of application of chromatic solfège is due to its short history, and imperfect vowel assignment for raised and flatted notes.
Transposition is a technical skill that requires not only intellectual understanding but also a lot of practice. Considering the work that needs to be done in order to achieve practical fluency, the difference that perfect pitch makes is too tiny to matter.
Over the years, I have come to realize more and more that the journey to better musicianship is different for everyone and one needs to know oneself well in order to choose the best way. Perfect pitch owners have their journeys and the rest of us have ours. Or if some of us do acquire perfect pitch, we may have yet another path in between. After all, certain skills enable us to approach music in certain ways. There are always other approaches.