Polkas and slides have a special place in Irish traditional music. They are very popular but a lot of musicians don't play them because they are very localized in origin (for the most part) from West Kerry and the Sliabh Luachra (which encompasses parts of Kerry, Cork and Limerick) and they require a special feeling to pull them off. They rely on more on back beat than the rest of Irish trad and are often very hard to play well if you are used to playing square tunes.
Polkas are a special challenge on the banjo and mandolin. Even thought he tunes are simple on paper, there is a lot going on especially when trying to emulate the lift that accordions and fiddles can get. In order to come close, we have to think in a different manner and play with a lot of down stroke emphasis.
Here is an example of polkas played very square and very badly. Note, however, that they are "authentic" in the sense that they are West Kerry polkas.
The Smith College Wailing Banshee ensemble is playing them with no back beat and no lift for the dancers. It sounds good at first until you hear the real thing.
Contrast this with Seamus Begley (who is from West Kerry) and Tim Edey:
Note the back beat, the tempo, and the enthusiasm of the players. They want you to dance.
Here are some well known Sliabh Luachra polkas from Jackie Daley and Seamus Creagh:
They are slightly different (the West Kerry and Sliabh Luachra musicians can tell the difference in a second) but still full of life and you want to move your feet due to the back beat. This is the essence of polkas and is what separates them from the other parts of Irish trad.
As a result, the rules for playing them on a banjo or mandolin go out the window. Back in the day, when I was writing for Mel Bay Banjosessions, I did a piece on how to play polkas on the banjo. Here is a video from that article:
The tune is simple, like most polkas, and I tried to emphasize the back beat. The main point I tried to make is that because of the emphasis on back beat, you have to play a lot of single down strokes in order to get the music to sound right. It takes a lot of listening to get it right and I don't think I quite got it in this video. In fact, every time I go back to Dingle, West Kerry, I have to re-learn how to play polkas and slides because if you are not around them a lot, you tend to fall into evil ways.
Enda Scahill teaches that alternate picking is the basis of all banjo playing (with the exception of jigs) but playing that way takes away some of the emphasis needed to carry a polka. Here is Brian McGillicuddy, of Cork, who showed us alternate picking on the mandolin. While he plays the polkas well, note that he plays single down strokes on some notes in order for the polkas to work.
In a concert or dance situation, Brian would be playing these tunes a lot faster, at least 130 bpm. He is playing to teach us the tunes here, but he can play at speed the way shown.
Trying to figure out polkas is not easy. They are simple tunes at 2/4 time that look easy but when played require that your head be in the groove for polkas. This is one music that absolutely has to be learned by ear. Here is my attempt at trying to play three polkas.
For Pluck Sake is another (and excellent) blog following the learning curve of two banjo players named Brendan (one is Breandan Mac Gabhann). Look it up. Lots of good information.
One more video. Enthusiasm! from Sliabh Notes. You have to play it on youtube, but it is worth it:
22 Dec 2015