Describe the techniques used for bending notes on a harmonica, explaining the mechanics of note bending and how it’s applied for expression.

Bending notes on a harmonica is a crucial technique for blues players, allowing them to access a wider range of notes and create the expressive, soulful sounds characteristic of the genre. Bending involves altering the pitch of a note by manipulating the airflow and the oral cavity, which effectively changes the resonant frequency of the reed. The mechanics of bending require precise control of the mouth, tongue, and breath.

The basic principle of bending involves creating a pressure difference between the mouth cavity and the air channels within the harmonica. To bend a draw note, which are the notes created by inhaling, the player needs to create a larger cavity in the mouth, and pull back the tongue. When you draw on the harmonica you are sucking air in through the harmonica, which causes the reeds to vibrate and create a note. By enlarging the oral cavity and lowering the back of the tongue, the player can lower the pitch of the note. This creates a low pressure in the mouth which is essential for bending draw notes. It is the same principle as creating a lower pitch by covering an opening on a bottle. When this is done properly, the draw note will drop in pitch to the desired note. The amount of air you draw, and the position of your mouth and tongue will control how low you bend.

To bend a blow note, which are created by exhaling, the player needs to do the opposite, using a small, tight oral cavity, and raise the tongue. When you blow into the harmonica you are blowing air through the instrument which vibrates the reeds to create a note. By making the mouth cavity tighter and pushing up with the back of the tongue the pitch will be lowered. This creates a high pressure in the mouth which is essential for bending blow notes. Similarly the amount of air you blow, and the position of your mouth and tongue will control how low you bend a blow note.

The tongue is one of the most important instruments in bending. Players will use their tongue to change the shape of the oral cavity which controls the amount of bend that they get. The tongue can also be used for articulation. When bending a draw note, the tongue is usually positioned further back in the mouth, which helps to enlarge the oral cavity, while when bending a blow note, the tongue is positioned more forward, which helps to make the oral cavity smaller. The tongue also controls the airflow and can be used to create different bend techniques. For example, a player might use the tongue to create a slow, deliberate bend by moving it slowly, or to create a quick, sharp bend by moving it more abruptly.

Breath control is also critical in bending, as it controls the stability of the note and the bend itself. You must have stable breath control to ensure that the note is not going up and down in pitch by accident. When bending, a player needs to be able to maintain a steady breath, and adjust the pressure and speed of the air to create the desired pitch and sound. The amount of air you breathe and the control of your airflow will also determine the quality of the note that you get. Beginners will often find that their bends sound a little bit rough. With practice they can learn to make their bends more fluid and smoother.

The notes that are easiest to bend on a harmonica are typically the draw notes. The 2, 3, and 4 draw notes on a diatonic harmonica are commonly bent. When playing a C harmonica in the second position (key of G) the 3 draw bent to the minor third is one of the most important blues notes. Blow notes can also be bent, especially on a harmonica with the proper reed setup for it, however they are often more difficult to bend than the draw notes.

The expression that comes from bending notes is central to playing the blues harmonica. The bends create the characteristic "blues notes" – the notes that are in between the notes of the major scale that give the blues their characteristic sound. Bends can be used to mimic the human voice, creating phrases that feel like moans, cries and calls, or simply to add a feeling of sadness. Players often combine bending with vibrato by subtly oscillating the tongue and airflow as they hold the bent note. Bends are often not just about hitting a note; they are also about how you get to that note, creating slides and glides by controlling the movement of the tongue. A skilled harmonica player can bend notes to different degrees, hitting half-step, whole step and sometimes even larger bends, each giving different qualities to the bends.

In summary, bending notes on a harmonica requires a combination of precise control of the mouth cavity, tongue, and breath. It's a nuanced technique that is central to blues harmonica playing, enabling musicians to create the expressive, soulful sounds that are characteristic of the genre and is used to emulate the human voice.