I have played the Highland bagpipe for more years than I care to remember, and have taught scores of students, some of whom have gone on to win gold medals in major competitions, and I have never heard of two kinds of D-throw.
There is only one “D-throw”, it is a movement that one cannot play on a six hole instrument like a whistle. Let me explain.
The bagpipe chanter’s range is only 1-1/8th octaves (which are represented on bagpipe written scores as “a” to “A”.) To accomplish this it has 8 holes, which must be covered by the thumb and first 3 fingers of the left hand and all four fingers of the right.
A “D throw” can be used as an ebellishment to go to “d” from any note other than low “a”. (To be technically correct I should add that, while possible to do so, in practice it is never used to separate two “d” notes.)
The movement.. written small and as 32nd notes … is “a-d-c”. To show how this goes, let’s represent melody notes in capitals and the movement in lower case. So lets say we are playing “E” and want to go to “D” with a D-throw. We close the chanter to play low “a” then throw our right fingers up to D with a little bounce off “c”
You can write it out on a staff thus
E a-d-c D. Getting a very heavy low “a” is essential to give this movement its effect.
In fact, I always told students to exaggerate the length of the low “a” a trifle by concentrating on hitting that hole good and hard, for the tendency of beginners is to fluff over so it becomes virtually inaudible.
The presence the r4 hole on a pipe chanter is crucial not only to making a D throw, but also many other other bagpipe movements such as the birl and the taorluath (which are much used in all pipe music,) and the crunluath, crunluach mach, crunluath fosgailte, which are usually encountered only in the pibroch ([piopbaireachd), the classic musical form peculiar to the Piob Mhor.
The high “A” note, played by the left thumb and also lacking on whistles, is also very important to pipe music not only because it
can be doubled with blinding speed but because it is such a weak note that it is easily masked into oblivion by the drones (which are an octave and two octaves lower but much louder.) When played in between quick lower notes, the effect is to emphasize the lower notes and make them sound staccato or separated by rests.
Since recorders have 8 holes, and chromatic fifes are being made with 10 holes I don’t see why whistles aren’t made with more than six to make the rich treasury of Scottish music available to whistle players. Where is the creative genius that brought us the bicycle, pneumatic tire, steam engine, linoleum, oatmeal, penicillin, golf and Dolly the Sheep?