Vocal registers are one of the most talked about - and yet still misunderstood - concepts in voice training. As far back as the 1970s, the Collegium Medicorum Theatri (CoMeT) - an international organization of voice specialists - formed a committee to attempt to clarify the concept of vocal registers. The fact that the debate still rages nearly fifty years later is an indication of how confusing this concept can be.
The confusion comes from the fact that the term 'register' means different things to different people. An accepted definition is that a register is 'a series of consecutive tones with similar properties'. But what those properties are depends on your point of view.
Although there is some correlation between the terminology of registers and the mechanisms involved in their production, it is important to differentiate between the terms 'mechanism' and 'register'.
The easiest way to make this distinction is by referring to Scientific registers (i.e. mechanical) and Singing registers (i.e. perceptual)
Using the Body-Cover model explained above, we can define 'registers' in terms of which parts of the vocal fold are vibrating - the Laryngeal Mechanism.
Research in recent years (by Natalie Henrich and others) has identified four different Laryngeal Mechanisms, numbered from 0 to 3:
The decision to number the Laryngeal Mechanisms rather than name them was made to move away from the confusing and inexact concepts of 'Head' and 'Chest' registers / voices.
But if you want to understand Laryngeal Mechanisms in other, more familiar terms:
You'll notice that 'Mix' and 'Middle' are listed as both M1 and M2. This is because singers access their 'Mix' in different ways, as explained below.
Although the vocal fold vibration can be determined precisely in terms of the laryngeal mechanism used, the sounds produced by an individual mechanism can have great variations in timbre and intensity, due to the shaping of the vocal tract.
Singers rely heavily on acoustic and perceptual feedback. Although this feedback is personal, it's vital to be able to discuss the voice with singers in these terms, as the sound and associated sensations are often all they have to go on.
But whatever you call the Voice Quality, the voice is still subject to the same natural laws and produced by physical structures. My personal approach is that it's fine to describe your voice in terms of how it feels and sounds to you - and to 'name' it accordingly - but an understanding of the mechanism producing that sound is very helpful, and can eliminate a lot of doubt and confusion.
Although flexible, the vocal folds still have physical limitations. As you sing higher in an M1 (Body and Cover, Thick, 'Chest') vibration, the vocal fold tissues stretch. Up to a certain higher pitch (different in every individual, but around B3 to F4) the Body is still involved in the vibration. Beyond that point, the Body can't stretch and it decouples itself, leaving the Cover to vibrate alone (M2, Thin, 'Head')
Similarly, when singing from high to low in an M2 vibration, the Cover will vibrate alone until you reach a certain lower pitch, at which point the Body will abruptly resume its vibration.
In an untrained singer, these transitions in and out of M1 and M2 wil be heard as 'breaks', 'cracks' and 'yodels'. A trained singer recognises these transition points and learns to manipulate other factors to minimize the effects.
Register transitions happen to all singers - the good ones just learn to disguise them!
The frequency ranges produced by two consecutive mechanisms partially overlap each other, sometimes by as much as an octave. Blending or 'mixing' (aka 'singing in the mix') is a vocal technique utilised in this overlap region, with the aim of disguising the transition from one mechanism to the other.
The aim of mixing is to simulate the sound quality of a different laryngeal mechanism (M2 when in M1, M1 when in M2) so that you can have Thick-sounding Thin folds and Thin-sounding Thick folds. This blending is realized by various means: adjusting the sound intensity and modifying the sound spectrum. For the voice geeks among you, the intensity adjustments required are approximately -10 dB to simulate M2 while in M1, and +5dB to simulate M1 while in M2.
It's very important to recognise that from a physical perspective there is NO separate 'middle' voice or 'mix' register - Mix is either M1- or M2+. But from an acoustic perspective, there's a very definite sensation of not being in a pure M1 or a pure M2 - hence why singers feel that a separate register exists.
The challenge for a professional singer is to learn how to maintain a certain mechanism beyond the limits of its natural attractor state, OR to allow the mechanism to change and manipulate other structures to keep the sound consistent.
A great technique comes from a solid understanding of the laryngeal mechanisms, and how they can be manipulated. Vocal fold mass, medial compression, resonance effects etc all contribute to the overall voice quality. Having independent, isolated control over each of these components gives the singer the ability to blend and adapt the sound in very subtle ways.
Every singer’s voice has to change mechanisms at various points in the range. The skilled singer learns to disguise those changes - hence why, to a listener, it can sound as though the singer is in the same mechanism. For example when you hear a female singer with a strong high note, you may well believe that she's singing in M1. But if that note is beyond the natural boundary of her M1, she's actually singing in M2 and making it sound like M1 - the definition of 'Mix'.
making different things sound the same
It's this misconception that often leads untrained or inexperienced singers to push and force the voice, mistakenly thinking that they can take M1 up to those higher pitches.
Think about it - the whole point of this technique is to disguise the natural physical changes that happen when you sing through your entire vocal range. If you can hear those changes, your technique is faulty!
The ideal technique in a nutshell: making different things sound the same.
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