Unfortunately, choosing the right tin whistle can be a confusing matter for several reasons:
1. Any single piece of music can be played in twelve different keys. A song in a major key can be transposed to eleven other major scales, and a song in a minor key can be transposed to eleven other minor scales. This means that even when you know what songs are going to be played, and even if you can find them in a book or online, you don’t necessarily know any of the keys that they will be played in. Very often singers will transpose the song to a different key without even noticing that they have done so. They aren’t trying to be difficult, they are just choosing a key (one of twelve choices) that feels right for their voices. Instrumental music (for example, most of the music found on thesession.org) is less likely to be transposed, but transposition is always an option.
2. Even if you know the key you will be playing in, you might not know what whistle to choose. This is because each whistle is capable of playing in several keys. For example, on a standard D tin whistle you can play easily in D, Em, G, Am and Bm. Depending on the piece of music and your ability, you might also be able to play in A, F#m, C and other keys without changing whistle.
3. To further complicate matters, the range of the song might not fit well on a tin whistle. Unlike a violin, guitar, or piano, the tin whistle only has a range of two octaves. This is plenty of range for simple songs like Twinkle, Twinkle or Mary Had a Little Lamb, but it can be a problem for other songs, especially if there are notes below the tonic. If you play a D tin whistle, you might expect D to always be the tonic (the home base and final note of most tunes), but inevitably, it is also the lowest note that you can play. This makes playing a song like Danny Boy impossible without altering the melody. A better option would be to transpose to G instead, without changing to a G whistle. But of course G might be the wrong key for the singer’s voice.
4. One last complication is that most tin whistle players only learn to read music for a D tin whistle. This means that when they use a Bb tin whistle, they still read the music as if they were playing on a D tin whistle. In other words they cover all the holes to play a D note, when really the note that they are playing will sound like Bb. To avoid confusion when communicating with other musicians, you should know about this automatic transposition. It can be troublesome, just as guitar players using a capo at the second fret might make the shape of a G chord and call it G even though all the other musicians will hear an A chord.
All this means that a knowledge of music rudiments and transposition is very important for tin whistle players. You will need to know the difference between a major scale and a minor scale, both of which can be played on any whistle, because the right scale must be chosen for each song. You should also know about modes which are variants of major and minor scales. Most of all, you should understand what transposition is, and how it works when playing on one whistle compared to changing whistles. And finally, as you have probably figured out by now, you’re going to want to buy more whistles.