Hand vibrato or "wah wah" is an effect which is used to add expression to harmonica playing. If you have ever seen a good harmonica player, it is likely that you have seen them using this technique.
To somebody watching, it looks like the player is waving or fluttering one hand back and forth while holding the harmonica with the other. The hand vibrato alters the flow of air through the harmonica, thus altering the sound.
When playing the hand vibrato, the right hand is moving between two basic positions. The first is formed by cupping the right hand around the left in its normal holding position, as shown in the photograph. The heels of both hands should be touching and the right hand fingers should curl up along the left hand little finger and around and upwards past the end of the left hand little finger and ring finger. This position results in the air being closed off by the two hands.
To complete the movement for the hand vibrato, the right wrist is swivelled slightly around to the right. This results in the "cup" being opened up and allowing air through. The wrist can then be swivelled back to the left to close the cup again. It is this movement back and forth that causes the vibrato or wah wah effect to sound.
The hand vibrato is indicated in the notation by a v above the note or chord to which it applies. Experiment with slow, medium and fast vibrato, there is no right or wrong speed for this technique, as different approaches will sound best in different musical situations.
This example applies the hand vibrato technique to single notes and chords.