6.4 The final step: identifying the speaker

Formant comparisons and identifying the speaker

After everything is broken down, all that is left for the system to do is the easy part–make a simple comparison between the input formants and the formant in thedatabase. The first step is in determining which vowel is actually being spoken. This is simply an examination of the location of thefirst two formant peaks. If they both fall within the range of a specific vowel’s first two formants, they are representing that vowel. That range is stored within the database. These ranges arevery well defined for each individual vowel and are adjusted to the members of the group. For example, the first formant of a vowel hasa range that will include formants at frequencies just above the highest frequency first formant in the group and just below thelowest frequency first formant. If it does not fall in the range of the vowel, that vowel is not the correct one, and it continues totry the next vowel. It repeats this process until either it finds a vowel or goes through all vowel sounds in the database. If theformants do not fall within any particular formant range, the vowel sound will be ignored.

The second step is the actual comparison. The frequency response of the input vowel sound is multiplied in a dotproduct with each member’s previously stored frequency response for the vowel. This is the vowel that was determined in the first step.A resulting score matrix is produced from the dot product. The score matrix will output a value from 0 to 1, with 1 being aperfect match and a 0 being an entirely incorrect match.

This process is repeated for each vowel sound in the word. The score matrices are then added together, and thesystem identifies the speaker as the individual with the highest score. If, however, that individual does not pass a thresholdvalue, then the system determines there is no match.