Phonation

The process of speech production by the human voice may be divided into phonation, resonation, and articulation. Phonation is the process by which energy from the lungs in the form of air pressure is converted into audible vibrations.

One method of phonation involves using the air pressure to set the elastic vocal folds into vibration, a process called voicing. The other involves allowing air to pass through the larynx in to the vocal tract where modifications of the airstream produce transient or aperiodic sound waves.

Aperiodic sounds can be combined with voiced sounds to create voiced consonants like /d/.

Aperiodic Phonation

Aperiodic phonation involves allowing air to pass through the larynx in to the vocal tract where modifications of the airstream produce transient or aperiodic sound waves.

Voice Vibrato

Included in the distinguishing characteristics of a musical sound which determine its timbre is vibrato/tremolo. The term vibrato for the singing voice is more commonly used to describe the variations in the voice during a sustained note. When analyzed, it is found that both the pitch and amplitude change periodically so that both vibrato and tremolo are present. The presence of vibrato, within limits, adds richness and expression to the voice. It is often the case that the amount of vibrato increases as a given note is sustained, and many singers use variations of vibrato for expression in singing. Excessive vibrato gives an impression of instability to the tone, so control of the amount of vibrato is a matter of practice and musical judgement.

This recording of a sustained vocal sound shows the periodic change in the amplitude of the sound. You could also clearly hear the accompanying periodic pitch change, so both amplitude modulation and frequency modulation were present.

If the precise harmonic content of a sustained voice sound is reproduced and sounded, the ear can easily distinguish the sound without the vibrato. Stanley suggests that a good vibrato rate for the singing voice is about 6 pulses per second, and that the average pitch variation is about a semitone accompanied by about 3 decibels of intensity variation. The amount of vibrato tends to increase with loudness, reaching about a full tone for very loud vocalization (fortissimo).

Vibrato with Musical Instruments

Included in the distinguishing characteristics of the sound of a musical instrument which determine its timbre is vibrato/tremolo. With a violin, almost pure vibrato (periodic pitch variations) can be produced with the finger on the string by a rocking motion which periodically changes the length and therefore the resonant frequency. Likewise a trombone player can produce almost pure vibrato by wiggling the slide in and out to change the pitch. On the other hand when a flute player uses the diaphragm to produce a tone variation, sometimes called "diaphragm vibrato", it is actually almost pure tremolo (periodic amplitude variation). For most tone variations which come under the general term vibrato, such as that produced with instruments employing a reed, the tone variation includes both true vibrato and tremolo since it is hard to produce a pitch variation without producing some amplitude variation as well. Voice vibrato also includes both pitch and amplitude variation.