Diaphragm control is fundamental for powering the tone from the dizi. It is the raw material from which the timbre of the sound emitted by the dizi can be shaped from. As such, one of the most important things to develop for a good tone is that of good diaphragm control.
We'll start with the mechanics of breathing needed, then talk about some control techniques. Note that these control techniques will be revisited in detail in a later series of articles listing the litany of ornamentation.
Mechanics of Breathing
Breathing for all forms of wind instruments is often the single most important variable that determines the quality of the tone, and it is naturally the same for dizi. Breathing for playing the dizi is a little more disciplined than that of normal day to day breathing, and can be classified in two main categories: deep or dantian (丹田) breathing, and shallow or shangfei (上肺) breathing.
Deep breathing is the basic form of diaphragm control that is needed when playing the dizi (and any other wind instrument). People do not normally breathe deeply unless they are yawning, and of course, yawning cannot be used as a means of breathing for playing the dizi.
There are two ways to think of deep breathing: the physiologically correct way, and the mental image projection way.
Physiologically, when one takes a deep breath, the diaphragm is allowed to flatten itself completely, almost always resting atop of the stomach. As a side effect, the abdominal walls (belly) tend to expand outwards to accommodate for the greater volume of space the lungs are taking up.
The mental image when breathing deeply is to imagine that one is ``breathing into the belly'' or breathing into one's dantian (丹田). The belly is often ``forced'' to expand out so that more air can be taken into the lungs.
In both cases, the net effect is that the lungs are allowed to fill up closer to their full capacity (technically no more than 80% for control purposes), and the air-stream that comes out from such deep breaths tend to be more full and resonant, characteristics that are important for long notes or in legato.
Such breathing often draws in the breath via the nose. The 80% of maximal lung capacity limit is for control reasons---anything more than that will amplify the effects of the initial ``rush'' on release. The ``rush'' is usually undesirable because it makes the tone sound irascible, forced, and uncontrolled, and if the required dynamics were low, impossible to meet.
Shallow breathing is the normal type of breathing that a person would do, except that in the case of the dizi, it is marked by ``breath snatching'' (qiangqi (抢气)), which is the use of the mouth to catch quick breaths in between notes. This type of breathing (and the tone that comes out of it) is mostly used for staccato playing. Sometimes we call shallow breathing shangfei (上肺) because it is a type of breathing that typically uses only the top 33% to 50% of the lung's capacity.
While considered ``shallow'', it is still important to flatten the diaphragm as much as possible when ``breath snatching'', i.e. to maximise the reservoir of air available to power the next tones. This is particularly important when the issue of dynamics control come into play.
``Mechanics of breathing'' covers only the means of generating the source of power behind the tone---it does not cover how the timbre of the tone can be manipulated. While most of the timbre control is via the buccal cavity, there are still a couple of control techniques that involve the diaphragm still. Here, we will talk briefly about vibrato and circular breathing---details will come in another future article.
Vibrato is related to deep breathing, but the ``belly'' now oscillates to impart a variation of the force behind the air-stream to give that wavering feel. It is also known as the fuzhenyin (腹振音). Whether the vibrato causes only an oscillation in tone amplitude (loudness) or tone frequency (pitch) is always up for debate because the air-stream controls both simultaneously.
Vibrato naturally uses more air, so the duration of the tone tends to be shorter than that of a regular deep breathing based one.
A seemingly uninterrupted air-stream that is produced through a combination of using the cheek muscles to store a reserve of air while blowing out to release it while taking in a deep breath via the nose, all the while managing the transition between cheek-lung and lung-cheek air so that the tone is uninterrupted.
Part of the difficulty is in the coordination between the cheek muscles and epiglottis to create seamless transitions. The air-stream exiting the buccal cavity cannot be broken, and there should not be any extraneous sounds that come from the epiglottis opening and closing.
Training Diaphragm Control
Good diaphragm control is trained with exercises revolving around variations of playing long tones, i.e. holding a tone for upwards of 8 seconds at a consistent dynamic. This is necessary to build up the stamina needed for all the other forms of breathing.
Some variations include playing in a crescendo, diminuendo, constantly loud dynamics, constantly soft dynamics. Playing larger (and therefore deeper) dizi can also help build up good breathing techniques because of the larger volume of air support needed.
``Breath snatching'' (qiangqi (抢气)) can be trained through specific etudes that work on single, double, and triple tonguing, techniques that will be talked about in a future article.
With good breathing techniques, it is hard to feel dizzy when playing a hard-driving piece.
One's ability to drive a good tone from breathing diminishes significantly when one is sick, mostly because the breath is too hot. Hot breaths tend to result in a weaker tone. This condition is also known as being qixu (气虚). Tone will tend to be off-pitch and it will become hard to sustain the correct dynamics at the correct duration. It is best to rest under such circumstances.