The vibrato is a most necessary part of any great singing voice. Not only is it a means of expression, but it is also a functional part of the vocal mechanism as it frees the voice of constriction and tension. A well managed vibrato can add tremendous emotive affects to a song or an aria. Therefore, it is crucial to understand the mechanics of the vibrato, as well as what can cause it to be negatively impacted.
Let us begin with an explanation of a proper vibrato action. A proper vibrato action is a fluctuation of pitch around a fundamental note being sung. Since there is a fluctuation in pitch it is important to understand that this fluctuation has a quantifiable oscillation and accent. The peak of the vibrato is about 1/3 above the fundamental pitch and 2/3's below the fundamental pitch. One might think that this would make the singer sound like that are singing out of tune, but this fluctuation also has a certain stress to it. The peak of the vibrato is approximately 5 decibels louder than the trough of the vibrato. As a result, the listener hears the voice centered in the fundamental pitch with the vowel being at its core. It is interesting to note that since there is this pitch oscillation the voice is rarely actually singing on the fundamental as it is going above and below it at all times. Conversely, when one is singing straight-toned the voice is always in the center of the fundamental pitch.
Additionally, the vibrato also has a certain ideal speed to it. This speed is determined by the number of pulses per second are achieved by the peak of the vibrato. Ideally this speed is at 6.2 pulses per second. In order to determine what the proper speed of the vibrato should be a test was done in which all of the greatest singers of the Golden Age of opera were studied. The figure of 6.2 pulses per second was an average of all of these amazing singers. However, there is also a window of acceptability with the speed of the vibrato. A singer can be a bit slower or a bit faster. As well the fluctuation can bit a bit more narrow,or wider, but it must not go past a certain point in either direction or it is no longer a functional, musical action of the singing voice. Instead it becomes an affect rather than an expressive tool.
It must be clearly stated that the vibrato action is semi-reflexive. That means that it will happen on its own, but a singer also be able to control it. This is comparable to blinking - it happens on its own, but you can control it also. Having control over the vibrato action is a vital tool of every singer. A singer should be able to sing straight-toned, speed up the vibrato or slow it down (within the confines of acceptability for expression), as well as make the fluctuation wider or more narrow. In fact, the louder one sings the bigger the vibrato is in amplitude. This kind of control not only is a means of artistic expression, but it also helps free the voice as the singer is able to increase its action when singing louder or higher. With the increase in amplitude the pulses of the vibrato must not slow down too much if at all. Otherwise it will become a wobble.
With the definition of the proper vibrato action comes the plethora of wrong vibrato actions or faulty movements of the voice. These movements are affects of wrong function or tension. There are several different forms of these actions:
1) Tremolo vibrato - is too fast and does not have enough or any fluctuation in pitch. It is entirely a reflexive action do to tension or a wrong connection in the brain signaling the muscles of the larynx. The latter problem is the hardest to fix.
2) Wobble - this is when the vibrato fluctuation is too great and the speed of the pulses is too slow. This is usually do to constrictive tension in the throat.
3) Inverted vibrato - this is when the accent of the fluctuation is skewed. It could be that the singer is accenting the trough too loudly or they are not getting the peak high enough above the pitch etc. this can make the voice sound different or even sharp depending on the issue. Many soprani who take out lower register from their voices end up with this problem.
All of these faulty vibrato issues are due to technical problems in the voice whether it is the wrong breathing coordination, improper vocal registration development or constriction. Knowing how the vibrato works and how to counter these issues is key. Unfortunately the vibrato is a very misunderstood vocal action. Hopefully this information helps singers understand the vibrato action properly. I will be covering more about the vibrato in later blog posts.