Cross-sectional studies of boys' voices
In a cross-sectional study, we visit the largest practical number of cases once. This allows us to identify broad patterns, associations and correlations, but a cross-sectional study can give a misleading picture of an individual for the simple reason that individuals are unique. The alternative is a longitudinal study in which we look at one individual repeatedly over time. This gives us a much better picture of how a voice develops, but another individual the same age might develop quite differently, so generalisations cannot be made. A classic error in musicology is to assume that voices "broke" at a certain age on the strength of only a small number of cases not studied longitudinally.
Mean Speaking Voice Pitch
The largest cross-sectional study I have undertaken was of the mean speaking voice pitch of boys aged between nine and fifteen. Between 2010 and 2012 over a thousand boys were seen in thirteen schools and nine choirs distributed across England, Scotland, Wales and the Isle of Man. Recordings were made of each boy counting backwards from twenty and reading the phonetic passage Arthur the Rat. The recordings were analysed for pitch and cross-referenced against age. This was done because at the level of a cross-sectional study the pitch of the speaking voice can be regarded as a suitable surrogate indicator of progression through puberty.The aggregate data are shown in the table below. The considerable range should be noted. For example, the highest twelve-year-old voice was 296Hz in pitch, which is undoubtedly pre-pubertal, whilst the lowest was 96Hz which is a certain indication of puberty completed. For this reason, the data are only meaningful as a population trend. Longitudinal study is necessary to determine the status of any individual. Here is a non-technical explanation of what it means for singing.
For a full and detailed account see chapter 5 of Dead Composers and Leaving Boys​
Child Voices
Boys develop proficiency in singing throughout childhood. By the time the speaking voice pitch has fallen from infant levels to anywhere between 220 and 290 Hz the boy is technically still a child, but voices that have been taught to access a singing rather than speaking register have been described by John Cooksey as optimal, and the "climax of beauty and fullness". Childish sweetness or "innocence" is still present, leading some listeners prefer the weightier and "fruitier" sound of the phase one voice (see below).
Pitch range of childhood phase 200-290Hz
Tanner stage 1.
Adolescent Voices
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Once the speaking voice has fallen below 200Hz, a boy may generally be considered to be adolescent (see below). The three phases below cover the period until a new baritone voice is finally established as puberty completes.
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Phase One
The voice will be a little deeper than that of a young child, but this deepening is not at first attributable to puberty. Most boys will still be soprano/alto, but preparations for change need to be in hand. The term "peripubertal" can be used to describe this time when boys are likely to approach and just cross the threshold of medical puberty.
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Pitch ranges of phase approx 195 - 215Hz​
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Tanner stage 1 , beginning stage 2
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Phase Two
Initially, the voice sounds slightly deepened to most ears, but still retains a boy-like timbre. This is gradually lost as puberty is now having an impact. Ideally boys should have a cambiata part, but if not possible, low alto is likely to be nearer than tenor. Onset of instability marks the end of the phase, when the voice starts to deepen much more rapidly.
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Pitch ranges of phase approx 170 - 199 Hz
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Tanner stages 2 and 3
Phase Three
The voice contunues and accelerates its rapid descent and many boys at first have difficulty adjusting their singing. "Boy-like" timbre is lost from the whole range which now sounds "young-man" like, causing some listeners to say it has "broken". The term "emerging baritone" conveniently covers what most boys will be able to do.
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Pitch range of phase approx 99 - 169 Hz
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Tanner stages 3 and 4
Perceptual Study
Two more cross-sectional studies were undertaken to explore these data further. The first was a perceptual study in which medical professionals and public-school music directors listened to ten voices 15Hz apart from the data base and allocated them to the three puberty/voice phases described in the Royal College of Paediatrics and Child Health adolescent growth standards.
This table indicates that a voice just below 200Hz is perceptually associated with the beginning of puberty whilst voices below about 160 Hz are perceived as “broken” and associated with the final stages of puberty. You can hear the test (and have a go yourself!) here. A full account is given in Chapter 3 of Dead Composers and Living Boys.
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Paediatric Clinic Study
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The final cross-sectional study was undertaken in collaboration with a consultant paediatric endocrinologist to establish an objective link between these perceptual judgements and recognised clinical measures of puberty. Sixty-two boys aged between ten and seventeen attending a clinic for measurement of puberty completed the same voice tests. It was then possible to state an objective relationship between pubertal development and speaking voice. This is shown in the graph and table.
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Here we can see a clear association between the voice pitch of 200 Hz and the medical standard for the commencement of puberty a testicular volume of 4 ml. This vindicates the perceptual judgements. Thus, the voices you can hear above listed in phase one are representative of what a boy sounds like when he is just beginning puberty.