The following charts show the position of the nodes and antinodes in the recorder's air column. There is one graph for velocity and one for pressure variations along bore.
The arrows show the direction of the vibrations.
The recorder's bore profile, and the open (o) and closed (x) holes are shown underneath.
Recorders have small holes, enabling the use of fork (or cross) fingerings for playing most of the semitones.
Normal fingerings
Opening a hole is theoretically equivalent to cutting off the vibrating
air column at that point, but the recorder's holes are too small for that,
so the velocity and pressure only diminish progressively beyond.
This is why fork fingerings like the one on the right are possible.
Fork fingerings
By using a fork fingering, leaving a hole open and closing the next
tone lower, because the open hole is too small to "cut off" the
vibrating air column. The note shown below is very different from
the one on the left.
= closed hole
These charts are for a baroque alto or treble recorder
If the holes were much larger, fork fingerings would not be possible.
A normal fingering with a large hole
If we could enlarge the holes to almost the same diameter
as the bore, we would obtain much higher notes, but they would also effectively cut the air
column when open, so nothing could happen lower down any more.
A fork fingering with a large hole
Fork fingerings have almost no effect with large holes, and closing
holes below an open one hardly changes the frequency of the
note being played. So the note shown below is very similar to the one on the left, and completely different from the one above.
= closed hole
These charts are for a baroque alto or treble recorder