I would like to hear more about recommended techniques for double stopping on concertinas.
My starting assumption is that a double stop is adding an additional note underneath a melody note, that additional note having the same duration as the melody note.
I have not studied formal music theory, but this is my "naive" understanding:
- "Double stops" generally refer to a technique on the violin/fiddle and other instruments of the violin family where a passage is played with two strings sounding simultaneously. Such a passage could be a single note or an entire piece, but is often just one or more parts -- from a few notes to a few measures -- of a piece.
- The additional (harmony) notes are not necessarily of the same duration as the melody notes, nor necessarily below the melody, though both are often the case.
- On a violin, the two notes must be played on adjacent strings, and that limits the potential harmonies. On a concertina (English, anglo, or duet) the options are much wider. (The bow can't skip a string between two other strings; the fingers can avoid any number of intervening buttons.)
- Playing more than two notes at a time is normally not considered an option on the violin, but "triple stops" and more are often accessible on the concertina.
Which melody notes should be double-stopped and which notes played as singletons? Long notes? Ends of phrases?
The only reliable rule is "whatever sounds good to your ear". Try harmonizing different groups of notes of different lengths at different places in the tune -- maybe even different segments of the tune on different repetitions, -- and pick one(s) that you like.
What intervals should be used between these two notes? I guess an obvious answer would be anything that sounds good but maybe there are some guidelines, such as concentrate on sixths, fourths, thirds and fifths? Maybe never more than an octave apart?
Your "obvious answer" is the only real answer. There is no definitive formula.
Nevertheless, the most-used bit of double-stopping harmony is parallel thirds, with the harmony either below or above the melody... maybe each in different parts of the tune. This is also the simplest on the English concertina, since it's the same pattern as playing the melody, but with two fingers at a time. But beware! If you try doing parallel thirds througout a piece, you'll almost certainly find places where it sounds "wrong". Then you would need to either drop the double stopping with those melody notes or use a different note (4th? 5th? 6th?) for harmony. (On an anglo, the arrangement of push and pull into "chords" can sometimes do that for you.) Harmony in parallel sixths involves a more "complex" pattern, but it's a "feeling" that can be learned.
Another simple "double stop" harmony would be a drone. That's an example where the harmony would not change every time the melody does. Or against an extended melody note, you could apply an upward or downward "run" as harmony.
Fiddlers/violinists use bowing and vibrato to accentuate double stops, should we do the same thing with bellows pressure and bellows shake?
"Should"? Only if it sounds good, in context.
What about sliding double stops? Any techniques to achieve that sound?
There's one song where I do that, but I don't recommend it as a general technique. Remind me next weekend, and I might try to record and describe it.
FInally, has anybody got some good examples that they can point at?
I'll try to gather a few links to things I've posted previously on concertina.net, but I'll post this now and make that a separate post.