Editing Recorder (musical instrument) (section)

== Acoustics ==
[[File:Recorder300.svg|thumb|Cross-section of the head of a recorder. A) block B) windway C) labium]]

=== Basic sound production ===
The recorder produces sound in the manner of a [[whistle]] or an organ [[flue pipe]]. In normal play, the player blows into the ''windway'' (B), a narrow channel in the ''head joint'', which directs a stream of air across a gap called the ''window'', at a sharp edge called the ''labium'' (C). The air stream alternately travels above and below the labium, exciting standing waves in the bore of the recorder, and producing [[Sound|sound waves]] that emanate away from the window. Feedback from the [[resonance]] of the tube regulates the pitch of the sound.

In recorders, as in all woodwind instruments, the air column inside the instrument behaves like a vibrating string, to use a musical analogy, and has multiple [[Overtone|modes of vibration]]. These waves produced inside the instrument are not travelling waves, like those the ear perceives as sound, but rather stationary [[standing wave]]s consisting of areas of high pressure and low pressure inside the tube, called nodes. The perceived pitch is the lowest, and typically loudest, mode of vibration in the air column. The other pitches are ''harmonics'', or ''overtones''. Players typically describe recorder pitches by the number of nodes in the air column. Notes with a single node are in the ''first register,'' notes with two nodes in the ''second register,'' etc. As the number of nodes in the tube increases, the number of notes a player can produce in a given register decreases because of the physical constraint of the spacing of the nodes in the bore. On a Baroque recorder, the first, second, and third registers span about a major ninth, a major sixth, and a minor third respectively.

=== Harmonic profile ===
The recorder sound, for the most part, lacks high harmonics and odd harmonics predominate in its sound with the even harmonics being almost entirely absent, although the harmonic profile of the recorder sound varies from recorder to recorder, and from fingering to fingering.<ref name=":4"/><ref name=":7" /> As a result of the lack of high harmonics, writers since [[Michael Praetorius|Praetorius]] have remarked that it is difficult for the human ear to perceive correctly the sounding octave of the recorder.

==== Air ====
As in organ [[flue pipe]]s, the sounding pitch of duct type whistles is affected by the velocity of the air stream as it impinges upon the labium. The pitch generally increases with velocity of the airstream, up to a point.<ref>{{Cite web|title = Pipe sensitivity|url = http://www.fonema.se/pipstiff/pipstiff.html|website = www.fonema.se|access-date = 11 February 2016}}</ref>

Air speed can also be used to influence the number of pressure nodes in a process called over blowing. At higher airstream velocities, lower modes of vibration of the air column become unstable, resulting in a change of register.

The air stream is affected by the shaping of the surfaces in the head of the recorder (the "voicing"), and the way the player blows air into the windway. Recorder voicing is determined by physical parameters such as the proportions and curvature of the windway along both the longitudinal and latitudinal axes, the bevelled edges (''chamfers'') of the windway facing towards the labium, the length of the window, the sharpness of the labium (i.e. the steepness of the ramp) among other parameters. The player is able to control the speed and turbulence of the airstream using the diaphragm and vocal tract.

==== Fingers ====
The finger holes, used in combination or partially covered, affect the sounding pitch of the instrument.

At the most basic level, the sequential uncovering of finger holes increases the sounding pitch of the instrument by decreasing the effective sounding length of the instrument, and vice versa for the sequential covering of holes. In the fingering 01234567, only the bell of the instrument is open, resulting in a low pressure node at the bell end of the instrument. The fingering 0123456 sounds at a higher pitch because the seventh hole and the bell both release air, creating a low pressure node at the seventh hole.

Besides sequential uncovering, recorders can use forked fingering to produce tones other than those produced by simple sequential lifting of fingers. In the fingering 0123, air leaks from the open holes 4,5,6, and 7. The pressure inside the bore is higher at the fourth hole than at the fifth, and decreases further at the 6th and 7th holes. Consequently, the most air leaks from the fourth hole and the least air leaks from the seventh hole. As a result, covering the fourth hole affects the pitch more than covering any of the holes below it. Thus, at the same air pressure, the fingering 01235 produces a pitch between 0123 and 01234. Forked fingerings allow recorder players to obtain fine gradations in pitch and timbre.

A recorder's pitch is also affected by the partial covering of holes. This technique is an important tool for intonation, and is related to the fixed process of tuning a recorder, which involves the adjustment of the size and shape of the finger holes through carving and the application of wax.

One essential use of partial covering is in "leaking", or partially covering, the thumb hole to destabilise low harmonics. This allows higher harmonics to sound at lower air pressures than by over-blowing alone, as on simple whistles. The player may also leak other holes to destabilise lower harmonics in place of the thumb hole (hole 0). This technique is demonstrated in the fingering tables of [[Silvestro Ganassi dal Fontego|Ganassi]]'s ''Fontegara'' (1535), which illustrate the simultaneous leaking of holes 0, 2, and 5 to produce some high notes. For example, Ganassi's table produces the 15th (third octave tonic) as the fourth harmonic of the tonic, leaking holes 0, 2 and 5 and produces the 16th as the third harmonic of the fifth, leaking holes 0 and 2. On some Baroque recorders, the 17th can be produced as the third harmonic of the sixth, leaking hole 0 as well as hole 1, 2 or both.