Source-Filter Model

The vocal cords produce a sound at the bottom of the throat. However, this is not what we hear coming out of the mouth. The shape of the vocal track filters out certain frequencies of the sound produced by the vocal cords, while letting other frequencies pass undampened (those corresponding to standing waves).

Thus when diagnosing our voices, we must determine whether the problem is with the source (our vocal cords) or the filter (the shape of the vocal tract).