If you are a stringed instrument player you might be accustomed to using a Snark or some other type of electric tuner to keep your strings in tune with one another. A funny thing happens when you rely on this device at an Irish session – you might not be in tune with the other instruments!
It’s not uncommon for a session to include fixed-pitch instruments such as concertina or accordion that cannot be re-tuned in the moment. If you’re lucky these fixed-pitch instruments are right on A440, but if they are a little sharp or a little flat you might have to tweak your strings to match.
This is why you’ll hear the concertina player sounding out his A note as people are tuning up. Players are supposed to use this as an opportunity to try and tune to the sound of that A. This is also why you’ll hear an experienced fiddler say to the accordion player “give me your A”. I suppose nothing can be done when both a concertina and accordion are present and they don’t match!
Even if you don’t have any fixed-pitch instruments at your session, the other musicians may attempt to tune to some proverbial “A” or to the sound of the loudest or most dominant instrument. At these times it is helpful to have your tuner handy so that you can offer a reference point to A440. Or just realize that – in a room full of folks who don't use electronic tuners – it’s not always you who is "out" of tune!
All of this can be difficult for the novice to pick up on. Even when you know what’s going on it can be difficult to tune by ear if you haven’t had much practice doing so. Just because you know what the accordion player's “A” sounds like doesn’t mean that you have the ear training to match that sound and, more importantly, to then also tune your G, D and E strings based on that A.
It might be a good idea to bring along a chromatic tuner that picks up ambient sound (not just the sound of your instrument) so that when the accordion player or concertina player is playing their A note that tuner will show whether it’s sharp, flat or right on the mark. That’s not the ideal method but it might help as a short-term solution.
I have a Casio keyboard at home which is pretty much at concert pitch so sometimes I’ll try and tune to that as practice. If I start out flat it’s easier to hear when it gets up to pitch than when I start out sharp and am coming from the other direction.