Concept

Formant — where it appears

A peak in the response of a resonator, fixed by its shape, that stays put while the notes played through it move. Which vowel is heard depends on where the peaks are relative to each other; who is speaking depends on the scale of the whole pattern.

Named by 16 essays across 3 fields — each of them below, with the objects they name alongside it.

The vowel in "hod", sung at 110 Hz. The partials of a 110 Hz note, each drawn at the amplitude the vocal tract's resonances give it. The peaks of the curve are the formants — 730 Hz and 1090 Hz — and they stay where they are when the pitch changes, because they are a property of the shape of the mouth and not of the note being sung.

A vowel is two resonances

The vowel in "heed" is the same vowel sung high or low, and nothing about it is a property of the note. It is two peaks in the response of the mouth, sitting at fixed frequencies while the partials of the voice slide underneath them.

timbre · Spectrum

Long-term average spectra: an orchestra, playing forte against a trained operatic soloist. Each source's mean spectrum over a long passage, in decibels below its own strongest region, on a logarithmic frequency axis. An orchestra, playing forte peaks at 250 Hz and is 30 dB down by 3,150 Hz; a trained operatic soloist peaks at 250 Hz and is 11 dB down by 3,150 Hz. The shapes are the same until about 1 kHz and separate above it: at 3153 Hz the difference is 19.0 decibels, which is the largest anywhere in the range. Nothing here is about level. Both curves are drawn against their own peaks, so what is being compared is shape.

One voice over ninety players

A soloist heard over a full orchestra is not louder than it and could not be. What the trained voice does instead is put a peak of energy at three kilohertz, which is where the orchestra's spectrum has already fallen away and where the ear's own threshold happens to be lowest. Nineteen decibels of advantage, in a place nobody is competing for.

timbre · The voice

The sound a listener knows best

A voice is recognisable across every vowel it says, across two octaves of pitch, down a bad telephone line and in a whisper where there is no pitch at all. Nothing that survives all of that can be a frequency. What survives is a ratio: the resonances of a vocal tract are set by its length, so a shorter tract multiplies every formant by the same factor, and identity is a scale on the spectral envelope rather than a position within it. Between an adult man and a child the whole pattern moves by a fifth, and the vowel does not change at all.

timbre · The voice

The note that moved by a minor third

A has been anywhere between 392 and 465 hertz in the surviving record, which is 296 cents — a minor third short of six. The usual conclusion is that absolute pitch level is a convention and nothing musical depends on it. That is true of everything written on paper and false of everything that happens in a throat or a body: a singer's register break sits at a fixed frequency, so across the historical range it lands three semitones further down the written page. Transposing a piece is not a uniform operation, because the performer does not transpose.

tuning · Pitch standard

How many intervals a duet is smooth at. Every ordered pairing of 5 radiators, with the number of wells in its dissonance curve over an octave from 262 hertz. Rows are the instrument underneath and columns the one above, so the grid is not symmetric about its diagonal and that asymmetry is the result. The count runs from 1 to 7 across the grid, and a cell and its mirror need not agree: a violin under a clarinet has 1 and a clarinet under a violin has 2. The fifth is a well in every one of the 25 pairings and no other interval is.

Which instrument is underneath

Every roughness curve so far compares two tones of the same timbre, which is a duet nobody plays. Give the two notes different instruments and the sum stops being symmetric: the same written interval, on the same two players, is up to five times rougher depending on which of them takes the lower note. From G3 upward the fifth is a well in all twenty-five pairings and no other interval is; below it, three pairings lose even that, and all three have a clarinet on top.

timbre · Spectrum

What the climb costs, in tonnes and in inharmonicity. The total string tension a piano frame carries at each historical standard, computed from the string scaling used here. Tension goes as the square of the pitch, so the climb from 392 to 465 hertz is a rise from 11.5 to 16.2 tonnes on one instrument. The same ratio runs the other way through inharmonicity, which is inversely proportional to tension: the same wire at 465 hertz has 29 per cent less of it than at 392, so its partials are that much closer to a true series.

What the climb was a search for

The four-hundred-year rise in the pitch standard is usually explained as a search for brilliance, and an earlier essay ended by asking whether that was even coherent: does raising a string's tension change its spectrum as well as its pitch? Mostly it does not. What changes the timbre is something else entirely, and it is a mechanism that applies to instruments with no strings at all — every filter in the chain is fixed in absolute frequency while the notes move against it, so raising the standard is not a brightening but a reshuffling, and some notes lose.

tuning · Pitch standard

Which pairs blend is a question about the note. The level at which a doubled pair's composite changes owner, drawn for all 15 pairs of 6 radiators over 2.6 octaves from 131 to 784 hertz. A pair blends when that level is inside the shaded band, which is the twenty-four decibels either way two players can manage; a curve outside it, or absent, is a pair one instrument owns at every balance. 6 of 15 pairs blend at the bottom of the range and 12 at the top. Every filter in this collection is fixed in frequency and the fundamental is not, so a radiator's shape is a function of pitch and so is everything computed from two of them — the blend ranking at the bottom and at the top disagree on 70 of 105 comparisons, which is more than half, so the order has turned over rather than merely shuffled.

The blend table has a row for every note

Eight earlier essays sound their instruments at one note, and one of them says why that cannot be innocent: every filter here is fixed in frequency and the fundamental is not. Swept over four octaves, the number of pairs that blend doubles from six to twelve, the ranking turns over rather than shuffles — seventy of a hundred and five comparisons swap — and a clarinet with an oboe goes from the best pair in the collection to the eleventh.

timbre · Spectrum

Partials 3, 4, 12 of "hod", over one vibrato cycle. The level of three partials of a 220 hertz note on the vowel in "hod", each about its own mean, over one cycle of a vibrato of ±71 cents at 6.0 hertz. The pale curve is the frequency deviation itself, for phase reference. Partial 3 at 660 hertz swings 4.22 decibels and peaks with the frequency; Partial 4 at 880 hertz swings 0.41 decibels and peaks twice a cycle; Partial 12 at 2640 hertz swings 8.62 decibels and peaks against it. The formants of this vowel are at 730, 1090, 2440 hertz and do not move; a partial below one rises as the frequency rises and one above it falls, so the modulations of a single note run in opposite directions at the same instant.

The partial that gets louder as it goes sharp

Eleven earlier essays sweep a set of partials and hold their amplitudes still, and a real tract does not move with the fundamental. Put the formant account and the sweeping account together and every partial acquires an amplitude modulation at the vibrato rate: 0.07 decibels on the fundamental and 8.6 on the twelfth partial of the same note. They are in phase below a formant and anti-phase above one — not ninety degrees apart — and the whole note swings 0.82 decibels, because they cancel.

instruments · The voice

Where a section's fluctuation stops being a beat, on 220 hertz. Two rates up the spectrum of a 220 hertz note sung by a section whose voices are spread by 15 cents. The rising line is the beat rate between a typical pair of them, which grows with the partial because a mistuning in cents is a difference in hertz that scales with frequency; it reaches the 15 hertz at which a beat stops being a beat by partial 5.5, at 1217 hertz. The flat line is the amplitude modulation the vibrato imposes through the formants, which is 6.0 hertz at every partial because the vibrato modulates every partial by the same number of cents at the same rate. The two are equal at 487 hertz. Above 1217 hertz the beating has become roughness and the only fluctuation left is the vibrato's — and that frequency is the same one an octave up, where it is partial 2.8 instead.

The rate that does not rise with the partial

Twelve earlier essays give every vibrato the same six hertz, and the measured spread is 5.5 to 7.5. Putting the two fluctuations a choir contains on one axis shows why the rate matters: the beating between mistuned voices rises with the partial and leaves the range a listener follows as fluctuation at 1,217 hertz, while the vibrato's own modulation is six hertz at every partial. Above that frequency a section fluctuates by vibrato alone — and if every singer had the same rate, it would barely fluctuate at all.

instruments · The voice

Every pair has a worst note, and for most of them it is at one end of the compass. The margin at the strike — how much nearer the composite spectrum sits to the decaying instrument's own spectrum than to the held instrument's, in decibels of log-spectral distance — for every ordered pair of six radiators at every semitone from C3 to C7, with the decaying instrument entering 6 dB above. violin over voice: worst −34.9 dB at E♭3, best 14.9 dB at C♯6, behind at 35 of 49 pitches; violin over clarinet: worst −2.2 dB at B♭4, best 19.6 dB at F♯6, behind at 3 of 49 pitches; violin over oboe: worst −0.3 dB at B♭4, best 11.4 dB at E3, behind at 1 of 49 pitches; violin over flue pipe: worst 2.7 dB at C7, best 16.9 dB at E3; violin over trumpet: worst −13.8 dB at B♭4, best −3.4 dB at D3, behind at 49 of 49 pitches; voice over violin: worst −9.2 dB at C♯6, best 41.8 dB at E3, behind at 8 of 49 pitches; voice over clarinet: worst 1.4 dB at C♯6, best 43.1 dB at E3; voice over oboe: worst −8.2 dB at C♯6, best 44.5 dB at E3, behind at 6 of 49 pitches; voice over flue pipe: worst −14.7 dB at C7, best 47.5 dB at E♭3, behind at 8 of 49 pitches; voice over trumpet: worst −24.2 dB at C7, best 39.5 dB at E3, behind at 20 of 49 pitches; clarinet over violin: worst −14.0 dB at F♯6, best 7.0 dB at B♭4, behind at 26 of 49 pitches; clarinet over voice: worst −36.6 dB at E3, best 3.5 dB at C♯6, behind at 46 of 49 pitches; clarinet over oboe: worst −14.2 dB at F♯6, best 5.5 dB at C3, behind at 27 of 49 pitches; clarinet over flue pipe: worst −14.5 dB at G6, best 13.3 dB at C3, behind at 18 of 49 pitches; clarinet over trumpet: worst −25.5 dB at F♯6, best −6.5 dB at C3, behind at 49 of 49 pitches; oboe over violin: worst −7.5 dB at E3, best 5.8 dB at B♭4, behind at 43 of 49 pitches; oboe over voice: worst −37.7 dB at E3, best 13.8 dB at C♯6, behind at 37 of 49 pitches; oboe over clarinet: worst −0.8 dB at C3, best 19.2 dB at F♯6, behind at 10 of 49 pitches; oboe over flue pipe: worst 2.4 dB at C7, best 14.3 dB at C3; oboe over trumpet: worst −14.2 dB at F4, best −12.8 dB at F♯6, behind at 49 of 49 pitches; flue pipe over violin: worst −12.7 dB at D3, best 3.0 dB at C7, behind at 43 of 49 pitches; flue pipe over voice: worst −40.4 dB at E♭3, best 19.4 dB at C7, behind at 34 of 49 pitches; flue pipe over clarinet: worst −7.7 dB at C3, best 18.9 dB at G6, behind at 24 of 49 pitches; flue pipe over oboe: worst −10.4 dB at C3, best 2.1 dB at C7, behind at 45 of 49 pitches; flue pipe over trumpet: worst −21.0 dB at C4, best −16.3 dB at C7, behind at 49 of 49 pitches; trumpet over violin: worst 8.7 dB at C3, best 17.3 dB at B♭4; trumpet over voice: worst −29.3 dB at E3, best 29.9 dB at C7, behind at 26 of 49 pitches; trumpet over clarinet: worst 10.7 dB at C3, best 30.6 dB at F♯6; trumpet over oboe: worst 16.9 dB at D5, best 18.8 dB at C7; trumpet over flue pipe: worst 21.2 dB at C7, best 24.7 dB at B♭3. A pale cell is a pitch at which the two spectra nearly coincide and the room has almost nothing to multiply; an unfilled cell is one at which the decaying instrument never leads at all.

A doubling's worst note belongs to one instrument, not to the pair

The essay before this one found one pitch at which a violin and a flue pipe nearly share a spectrum and asked which pitch that is for every pair. Run over six radiators, thirty ordered pairs and forty-nine semitones, the answer is that seventeen pairs choose a worst note and thirteen simply run out of compass — and that the seventeen do not choose thirty different notes. They cluster in fours and threes, and each cluster is one instrument's own filter: the violin's worst note is B flat 4, its strongest body resonance; the clarinet's is F sharp 6, its cutoff; the voice's is C sharp 6, where its second partial meets its second formant. A doubling fails at a note that belongs to one of its players.

timbre · Spectrum

Inside the compasses the instruments have, 8 of the map's seventeen worst notes cannot be played by both. The margin at the strike for every ordered pair of six radiators from C3 upward, with every note outside the pair's shared compass greyed: the violin from G3 to E7, a soprano from C4 to C6, a B♭ clarinet sounding D3 to B♭6, the oboe B♭3 to A6, a B♭ trumpet sounding E3 to B♭5, a flue pipe throughout. violin over voice: shared C4 to C6, worst inside it −30.6 dB at C4; violin over clarinet: shared G3 to B♭6, worst inside it −2.2 dB at B♭4; violin over oboe: shared B♭3 to A6, worst inside it −0.3 dB at B♭4; violin over flue pipe: shared G3 to C7, worst inside it 2.7 dB at C7; violin over trumpet: shared G3 to B♭5, worst inside it −13.8 dB at B♭4; voice over violin: shared C4 to C6, worst inside it −5.9 dB at C6; the full map's worst, C♯6, is outside; voice over clarinet: shared C4 to C6, worst inside it 6.9 dB at F♯5; the full map's worst, C♯6, is outside; voice over oboe: shared C4 to C6, worst inside it −3.4 dB at C6; the full map's worst, C♯6, is outside; voice over flue pipe: shared C4 to C6, worst inside it −2.5 dB at C6; voice over trumpet: shared C4 to B♭5, worst inside it −12.6 dB at F♯5; clarinet over violin: shared G3 to B♭6, worst inside it −14.0 dB at F♯6; clarinet over voice: shared C4 to C6, worst inside it −31.3 dB at C4; the full map's worst, E3, is outside; clarinet over oboe: shared B♭3 to A6, worst inside it −14.2 dB at F♯6; clarinet over flue pipe: shared D3 to B♭6, worst inside it −14.5 dB at G6; clarinet over trumpet: shared E3 to B♭5, worst inside it −22.7 dB at A♭5; the full map's worst, F♯6, is outside; oboe over violin: shared B♭3 to A6, worst inside it −6.0 dB at E4; the full map's worst, E3, is outside; oboe over voice: shared C4 to C6, worst inside it −33.0 dB at C4; the full map's worst, E3, is outside; oboe over clarinet: shared B♭3 to A6, worst inside it 0.2 dB at B♭3; oboe over flue pipe: shared B♭3 to A6, worst inside it 4.2 dB at A6; oboe over trumpet: shared B♭3 to B♭5, worst inside it −14.2 dB at F4; flue pipe over violin: shared G3 to C7, worst inside it −11.3 dB at G3; flue pipe over voice: shared C4 to C6, worst inside it −34.8 dB at C4; flue pipe over clarinet: shared D3 to B♭6, worst inside it −7.7 dB at D3; flue pipe over oboe: shared B♭3 to A6, worst inside it −10.4 dB at B♭3; flue pipe over trumpet: shared E3 to B♭5, worst inside it −21.0 dB at C4; trumpet over violin: shared G3 to B♭5, worst inside it 9.1 dB at F4; trumpet over voice: shared C4 to B♭5, worst inside it −22.4 dB at C4; the full map's worst, E3, is outside; trumpet over clarinet: shared E3 to B♭5, worst inside it 11.0 dB at E3; trumpet over oboe: shared B♭3 to B♭5, worst inside it 16.9 dB at D5; trumpet over flue pipe: shared E3 to B♭5, worst inside it 22.7 dB at B♭5. Of the seventeen worst notes the full map chose, 8 lie outside a compass and 9 inside.

Half the worst notes of a doubling are notes nobody can play

A map of where two instruments' spectra come closest found seventeen pairs with a worst note of their own, gathered into four clusters, each belonging to one instrument's filter. It drew every instrument over the same five octaves. Read inside the compass each pair can actually play, eight of the seventeen worst notes are out of reach — the voice's C♯6 lies a semitone above a soprano's top C, and its E3 below her lowest note — and two pairs that seemed only to run downhill turn out to have a worst note after all. Of the four clusters, only the violin's B♭4 is advice every pair in it can use.

timbre · Spectrum

A vibrato hides a section's beats above about four hundred hertz. Two voices of a section whose tuning is spread by 15 cents, singing one note: how many nulls of their beating a listener can follow each second — counted only while the beat is at or below fifteen a second — at the frequency of the partial compared, sung straight and with a 71-cent vibrato at about six hertz. 220 Hz 2.2 straight, 5.3 with vibrato; 330 Hz 3.3 straight, 4.4 with vibrato; 440 Hz 4.2 straight, 3.9 with vibrato; 550 Hz 5.0 straight, 3.3 with vibrato; 660 Hz 5.1 straight, 2.8 with vibrato; 880 Hz 5.5 straight, 2.4 with vibrato; 1100 Hz 4.8 straight, 2.0 with vibrato; 1320 Hz 4.6 straight, 1.5 with vibrato; 1760 Hz 3.9 straight, 1.2 with vibrato; 2200 Hz 3.5 straight, 1.1 with vibrato; 2640 Hz 3.2 straight, 0.9 with vibrato; 3200 Hz 2.3 straight, 0.7 with vibrato; 3520 Hz 2.0 straight, 0.7 with vibrato. Below 413 hertz the vibrato adds followable beats, because it sweeps a slow difference faster. Above it the vibrato removes them, because it carries the pair's difference past fifteen hertz most of the time; at 3,200 hertz, the singer's formant, a straight section gives 3.4 times as many.

A vibrato hides a choir's tuning above four hundred hertz

Thirteen essays drew a vibrato that had always been running; a real one grows out of a straight tone over the first quarter-second of a note. Counting the beats a listener can follow between two voices of a section shows what that front edge is worth. A vibrato takes most of a section's countable beats away above about 400 hertz — seven in ten of them at the singer's formant — and adds some below. The straight start gives them back only while the vibrato is still growing, and in the band where a voice carries that is less than one beat.

instruments · The voice

A choir's vibratos must lock to two milliseconds

A vibrato hides a section's mistuning from a listener counting beats, and the obvious way it could stop hiding it is for the singers' vibratos to move together. They would have to move very nearly together. Half-entrained vibratos leave a section as hidden at the singer's formant as independent ones; locked to nine-tenths they expose three-quarters of what a straight section does; only past nineteen parts in twenty does the section's tuning show as if they sang straight. At six cycles a second that is two vibratos peaking within two milliseconds of each other — and the better a section is tuned, the tighter the lock has to be.

instruments · The voice

Heard a little late, two vibratos lock in step; heard a third of a cycle late, they lock in opposition. Two singers' vibratos at 6.0 and 6.2 a second, each pulled towards the phase it hears from the other with a strength of 10 radians a second, the hearing delayed by a stated time: how far apart the two vibratos' peaks settle, in milliseconds, after twenty seconds. 0 ms: 1.6 apart (4°); 20 ms: 2.4 apart (5°); 40 ms: 61.9 apart (-169°); 60 ms: 70.7 apart (-176°); 80 ms: 79.5 apart (-176°); 100 ms: 88.1 apart (-176°); 120 ms: 95.7 apart (-175°); 140 ms: 1.6 apart (4°); 160 ms: 1.6 apart (4°); 180 ms: 1.8 apart (4°); 200 ms: 69.6 apart (-176°). Under about forty milliseconds the lock is near in phase; from about forty to a hundred and twenty it is near antiphase, the peaks most of half a cycle apart; from about a hundred and forty, nearly a whole cycle late, it is near in phase again. The shaded band is the two milliseconds the formant asked for.

Singers who hear each other late lock their vibratos in opposition

A choir's vibratos give back the section's tuning at the singers' formant only if they are locked to within about two milliseconds. Singers who lock do it by hearing each other, and they hear each other late. Two vibratos pulled towards what each hears of the other settle near in step while the delay is under about forty milliseconds, and even then come within two milliseconds only if each singer corrects a phase error in about thirty. From forty to a hundred and twenty milliseconds late — a third to two-thirds of a vibrato cycle — they lock in opposition, peaks seventy to ninety milliseconds apart, and hide the section's tuning more completely than vibratos that never locked at all.

instruments · The voice

Where a pair would lock in opposition, a section of sixteen does not lock at all. Sixteen singers in two rows of eight, sixty centimetres apart, each hearing every other after the sound's travel and a common latency, each vibrato pulled towards all it hears with a total strength of 10 radians a second; four draws of rates and phases. Against the latency: R1, the length of the mean of the vibratos' phases, one when every vibrato is in step; and R2, the same for twice the phases, one also when the section has split into two opposed halves. 0 ms: 0.96, 0.86; 10 ms: 0.94, 0.83; 20 ms: 0.89, 0.71; 30 ms: 0.72, 0.52; 40 ms: 0.47, 0.31; 50 ms: 0.09, 0.24; 60 ms: 0.07, 0.22; 70 ms: 0.08, 0.23; 80 ms: 0.08, 0.22; 90 ms: 0.10, 0.24; 100 ms: 0.19, 0.22; 110 ms: 0.68, 0.46; 120 ms: 0.90, 0.73; 135 ms: 0.96, 0.85; 150 ms: 0.97, 0.87. A section split in two would show R2 high with R1 low; it never does.

Sixteen singers cannot all oppose each other

Two singers who hear each other a third of a vibrato cycle late lock their vibratos in opposition and hide their tuning better than if they had not listened at all. Sixteen cannot do it, because no arrangement puts every one of them opposite every other. At the latencies where a pair opposes, a section of sixteen does not lock at all: each singer keeps a vibrato rate of its own, and a listener hears the section's tuning exactly as through independent vibratos. Outside that band the section locks in step and gives most of its tuning back. A section that listens to itself can expose its tuning or leave it as it was, but never hide it.

instruments · The voice

A row that hears its neighbours late hides the tuning between them, exposes it between every second singer, and leaves the whole as it was. Sixteen singers in one row sixty centimetres apart, a draw of fifteen cents apart with 71-cent vibratos, each pulled at ten radians a second towards what it hears, each voice's pull weighted by the inverse of its distance to the power 8; four draws. The beats a second a listener can follow at 3,200 hertz, against the latency, for neighbouring pairs, for pairs two places apart, and over every pair. neighbours: 0 ms 1.62, 20 ms 1.36, 40 ms 0.69, 60 ms 0.30, 80 ms 0.28, 100 ms 0.29, 120 ms 0.78, 150 ms 1.63; every second singer: 0 ms 1.23, 20 ms 0.90, 40 ms 0.82, 60 ms 0.94, 80 ms 1.21, 100 ms 1.15, 120 ms 0.90, 150 ms 1.21; every pair: 0 ms 0.96, 20 ms 0.77, 40 ms 0.72, 60 ms 0.67, 80 ms 0.67, 100 ms 0.69, 120 ms 0.75, 150 ms 0.92. Sung straight 2.33, independent vibratos 0.68, a pair in opposition 0.19.

A row that hears its neighbours moves its tuning, it does not hide it

Sixteen singers who all hear each other alike cannot lock in opposition, because opposition between every pair is impossible. A row that hears mainly its neighbours has no such obstacle — opposition along a chain is consistent — and at the latencies that make a pair oppose, it half-alternates: neighbours opposite each other, every second singer nearly in step. That hides the tuning between neighbours as well as a duet hides it, and exposes it between every second singer more than independent voices would. Over the whole row the two cancel to the hundredth. With no latency, the same local hearing stops the row locking at all, and hides nearly half of what a whole-row lock would show.

instruments · The voice

Named alongside it

The objects these essays reach for when they reach for this one.

Modulation Vibrato Beating Source-filter Unison Register Spectrum Orchestration Resonance Roughness Critical bandwidth Spectral envelope

All concepts