 The sound wave created by a sound source is referred to as the fundamental frequency or F0. On a musical instrument, F0 is the result of the vibration of a piece of reed, a string or lip vibration. In speech, F0 is the result of vocal fold vibration. In both cases, F0, normally a complex sound wave, is filtered. That is, it is intensified and damped by numerous parts of the resonating body, which, in the case of a guitar, is the whole resonating body. The resulting bundles of resonance frequencies or harmonics are multiples of F0. They are called formants and are numbered F1, F2 and so on. In speech, the situation is more complicated, since the formant pattern of a speech sound is the outcome of the whole vocal tract, working as one resonance system and there are several resonance chambers, the pharynx, the aural cavity, the nasal cavity and the skull, where the pharynx and the aural cavity have shown to be the most important. They are associated with F1 and F2. Unlike on musical instruments, in speech the resonance chambers are subject to changes depending on the type of speech sound. In vowels such as E and R, we have different resonance chambers and thus different values for F1 and F2. Even though all speech sounds can be associated with specific formant patterns, aspects such as interspeaker variation that is different F0 input and different vocal tract sizes and shapes, and additional noises complicate the situation.