Solfeggio frequencies: meanings and evidence

What are the nine Solfeggio frequencies?

The set runs 174, 285, 396, 417, 528, 639, 741, 852 and 963 Hz. Six of the tones, from 396 Hz to 852 Hz, carry the syllables UT, RE, MI, FA, SOL and LA from a medieval hymn, in that order. The other three were added later and carry none. 528 Hz sits in the middle of the set and is the best known, and 963 Hz closes it at the top.

Each tone also travels with a meaning, across playlists, tuning forks and apps. The table gives the meaning Harmonance uses on each tone's page and what has actually been tested in people. The sections below explain where each column comes from.

The nine tones, their meanings and testing

Tone	Meaning	Tested in people
174 Hz	Comfort and grounding	Two listeners in one pilot
285 Hz	Restoration	No listening study found
396 Hz	Release and steadying	Two listeners in one pilot
417 Hz	Change and clearing	No listening study found
528 Hz	Love and renewal	A few small studies, mixed
639 Hz	Connection and communication	Two listeners in one pilot
741 Hz	Expression and clarity	One skin response study
852 Hz	Inner listening	One skin response study
963 Hz	Stillness and unity	Two listeners in one pilot

Where does the name Solfeggio come from?

Solfeggio is the Italian word for singing by syllables, the do, re, mi of every singing lesson. The syllables come from a Latin hymn to Saint John the Baptist, Ut queant laxis, sung at Vespers on his feast day, 24 June. Each half line of its first verse starts one note higher than the last, so the first syllables, UT, RE, MI, FA, SOL and LA, fall on the first six notes of the scale of C.

The six half lines and the note each begins on

Half line	Syllable	First note
Ut queant laxis	UT	C
resonare fibris	RE	D
mira gestorum	MI	E
famuli tuorum	FA	F
solve polluti	SOL	G
labii reatum	LA	A

In Richard Tarrant's translation, the verse asks for one thing, a free voice to sing with:

So that your servants may sound forth the wonders of your deeds with loosened hearts, remove the guilt of our tainted lips, Saint John.

Who wrote the words is uncertain. A medieval writer, Durandus, said Paul the Deacon composed the hymn when he was hoarse and due to sing at Easter, asking for the help that Saint John's father found when his voice returned. Some editors doubt that Paul wrote it at all.

The hymn became a teaching tool in the eleventh century. Guido of Arezzo, a monk who trained choirboys, used it so that singers could find any note by remembering how the hymn began on it. He described the method in a letter to a fellow monk, Michael, written no later than 1032, the year the pope it describes him meeting, John XIX, died. Sir John Hawkins's history of music sums up Guido's claim: his boys learned to sing "in no greater a space of time than three days what they could not have mastered by any other method in less than many weeks".

Whether Guido himself named the notes after the syllables is disputed; one scholar argued that the names grew out of the habit. Two later changes gave the familiar scale. UT became DO, which is easier to sing, and a seventh syllable, SI, was made from the initials of the hymn's last words, Sancte Ioannes.

None of this involved numbers. The syllables named steps of a scale, not fixed pitches: in medieval practice the same syllable did not always sit on the same note, and nobody could yet measure how fast a string vibrates. The hymn gives the Solfeggio frequencies their name and their syllables, and nothing more.

Where do the Solfeggio numbers come from?

The numbers first appear in a book printed in 1999, Healing Codes for the Biological Apocalypse, by Leonard G. Horowitz and Joseph Puleo. The Library of Congress catalogues it under subjects that include prophecy and numerology. Its publisher's press release says the co-author was "intuitively guided to find the pattern of six repeating codes in the Book of Numbers, Chapter 7, verses 12 through 83".

The method is simple enough to check at home. Numbers 7 describes twelve days of offerings, and each day takes six verses, from verse 12 to verse 83. Take three verse numbers six apart, add up the digits of each until one digit is left, and read the three digits as one number. Verses 12, 18 and 24 give 3, 9 and 6: 396. Verses 13, 19 and 25 give 4, 1 and 7: 417. Starting from each verse from 12 to 17 gives the book's six numbers.

Verse numbers in Numbers 7 and the digits they reduce to

Start	Verses	Digits	Number
12	12, 18, 24	3, 9, 6	396
13	13, 19, 25	4, 1, 7	417
14	14, 20, 26	5, 2, 8	528
15	15, 21, 27	6, 3, 9	639
16	16, 22, 28	7, 4, 1	741
17	17, 23, 29	8, 5, 2	852
18	18, 24, 30	9, 6, 3	963
19	19, 25, 31	1, 7, 4	174
20	20, 26, 32	2, 8, 5	285

Three things follow. The rule reads only the verse numbers, never the words. Those numbers are far younger than the text: Hebrew verse numbers are usually credited to a concordance made around 1440, and the first English Bible with both chapters and verses was the Geneva Bible of 1560. And nothing about the rule is special to Numbers 7. Any three verse numbers six apart give one of the same nine results, so verses 1, 7 and 13 of any long chapter give 174.

Horowitz did not present the book as music scholarship. Replying to a reviewer, he wrote:

We ask forgiveness for our limited knowledge in the fields of music and physics

The lowest two tones and the highest, 174, 285 and 963 Hz, are not in the 1999 book, and who first added them is not recorded. A tuning fork maker's page later asked "Why 6 forks when others have gone to 9?", and a trademark application filed by Horowitz in February 2007 lists all nine. Carry the verse rule on to starts 18, 19 and 20, as the table shows, and it gives exactly those three numbers.

Where do the Solfeggio meanings come from?

The meanings arrived after the numbers. By the end of 2002, the tuning fork site of a sound teacher, David Hulse, paired each of the six with a syllable and a purpose: UT, 396 Hz, "Liberating Guilt and Fear", and RE, 417 Hz, "Undoing Situations and Facilitating Change". A 2006 copy of his site explains how: he looked at the definitions of each syllable, using what he called hidden entries in Webster's Dictionary, and from them assigned a use to each tone.

So the meanings are a modern reading of Latin syllables through an English dictionary, not a teaching handed down from medieval singers. Harmonance uses gentler names on each tone's page, such as grounding for 174 Hz and stillness for 963 Hz, and offers them as intentions to listen with. The guide to chakras and frequencies follows the body maps that later attached to the same tones.

Are the Solfeggio frequencies a musical scale?

Not in any sense a musician would use. The hymn climbs six notes in whole and half steps. The six numbers of 1999 climb unevenly: 417 sits less than one piano key above 396, and 528 is then four keys higher again. Set on the same ladder of piano keys, the two climbs part company from the second step.

Piano keys (semitones) above the first note

Hymn	Keys above UT	1999 number	Keys above 396 Hz
UT	0	396 Hz	0
RE	2	417 Hz	0.89
MI	4	528 Hz	4.98
FA	5	639 Hz	8.28
SOL	7	741 Hz	10.85
LA	9	852 Hz	13.26

Pitch was not something the medieval world could measure. Grove's dictionary of music admits "no positive data as to the pitch used in the earliest music". The first known estimate of how many times a second a note vibrates is Marin Mersenne's, in 1636, six centuries after Guido. The hertz entered the international system of units in 1960, and the A at 440 Hz that tunes most music today was agreed at a conference in London in 1939.

One of the numbers does have an older musical history. Grove records that in 1834 a congress of physicists at Stuttgart adopted Johann Scheibler's proposal to fix A at 440, with "true C = 528". The arithmetic is plain: 528 is 440 times six fifths, the pure minor third above that A. So 528 Hz was an ordinary C a century and a half before 1999, with no hymn involved. Two of the original six also sit in a simple ratio: 396 and 528 are 3 to 4, a pure fourth.

Against a modern piano tuned to A at 440 Hz, the nine tones scatter. Five sit close to a key: 174 Hz near F, 396 Hz near G, 417 Hz near G sharp, 528 Hz near C and 741 Hz near F sharp. The other four, 285, 639, 852 and 963 Hz, fall almost halfway between two keys, about a quarter tone from either. The set is not a scale you could play on a standard piano. It works best the way it is usually heard, one held tone at a time. The guide to 432 Hz and Pythagorean tuning covers how tuning standards came about.

Why do the Solfeggio numbers add up to 3, 6 and 9?

Add up the digits of any of the nine and keep going until one digit is left. 174 gives 12, then 3. 528 gives 15, then 6. 963 gives 18, then 9. Every tone ends on 3, 6 or 9, and tuning fork makers pointed to the pattern as a sign that the set is special.

The arithmetic behind it is ordinary. All nine numbers are multiples of 3, and adding up a number's digits keeps its remainder after dividing by 9, the old bookkeeper's check called casting out nines. A multiple of 3 can only end on 3, 6 or 9. Any other multiple does the same: 222 gives 6, and 450 gives 9.

The set does have more order than that. Laid out in rows of three, each row climbs by 111: 174, 285, 396, then 417, 528, 639, then 741, 852, 963. Each column reuses the same three digits in turn, as 174, 417 and 741 do, and the three columns use exactly the digits of the three columns of a phone keypad: 1, 4 and 7; 2, 5 and 8; 3, 6 and 9. In the star below, each column is one triangle.

The three digit families

Digits	Tones	Digit sum	Reduces to
1, 4, 7	174, 417 and 741 Hz	12	3
2, 5, 8	285, 528 and 852 Hz	15	6
3, 6, 9	396, 639 and 963 Hz	18	9

None of this depends on sound. The pattern belongs to writing numbers in tens. Write the same tones in another base, as a computer does in binary, and the digit sums no longer fall on 3, 6 and 9. That is why the pattern can be lovely to look at and still say nothing about how a tone sounds. The guide to angel numbers looks at number symbolism more widely.

What does research say about Solfeggio frequencies?

Very little, and most of it concerns 528 Hz. No large, blinded trial has yet compared a Solfeggio tone with an ordinary tone while listeners did not know which they heard. That is the test that would separate a number from the music, the quiet and the expectation around it, and it is the design of a small double-blind pilot that compared music tuned to 432 Hz and to 440 Hz.

528 Hz. In a study of nine adults, the same piano music was played in a 528 Hz version and the standard 440 Hz version on different days. Saliva readings of cortisol and oxytocin shifted only after the 528 Hz version, but each version was compared only with its own starting point, never with the other, and nine people cannot settle anything. The authors' own abstract is plain:

Various effects have been ascribed to the solfeggio frequency, but none of these have any scientific basis.

A larger trial randomised 162 students to 20 minutes of silence, "528 Hz" music or "432 Hz" music before an exam. Its abstract reports two saliva markers higher after the 528 Hz music, but the paper's own results call one of them comparable with silence, and an attention test showed no difference between the groups. Comparing music with silence also cannot single out the tuning.

The rest is animals. Rats exposed to a 528 Hz tone at a very loud 100 decibels showed changes in brain chemistry, and zebrafish played "solfeggio-frequency music" did better on a memory task after a day of constant light. Neither can say what a tone does for a person listening at home, and the zebrafish abstract does not name its frequencies.

The other tones. A Japanese pilot played five of the tones, 174, 396, 528, 639 and 963 Hz, to two people each, with no comparison group, and its authors say comparing the frequencies was not its purpose. A study of six pure tones reports that 741 and 852 Hz raised skin conductance, a sign of arousal, though its size and controls could not be checked. For 285 and 417 Hz no listening study was found: a 2025 preprint claims twelve studies of 417 Hz, but the 417 Hz papers it cites could not be traced in PubMed or Crossref. Even a 2026 review that favours the tones concedes "little direct empirical evidence" for 639, 741 and 852 Hz.

174 Hz as a base tone. Several studies of binaural beats, which play a slightly different tone in each ear, have used 174 Hz as the base, such as a week-long study with twenty students. They test the beat between the ears, not 174 Hz itself; the guide to brainwave frequencies explains the difference between a carrier pitch and a beat.

For music in general, the US National Center for Complementary and Integrative Health puts it this way:

However, because much of the research on music-based interventions is preliminary, few definite conclusions about their effects have been reached.

So the honest summary is short. The Solfeggio frequencies are a modern tradition built on a number game, and research has not singled out any of them. A fact-check by Science Feedback reaches the same view of their origin, and the music scholar Robin James found that the method "has nothing to do with any of the math behind" Western music theory. The tones can still be pleasant, steady sounds to sit with, which is how Harmonance offers them. The guide to the science of sound healing covers the wider evidence.

What do listeners say about the Solfeggio frequencies?

Comments under the Harmonance videos show how differently the same tones land. They are quoted whole, without names. Under the Solfeggio scale journey, which climbs from 174 to 963 Hz:

pure power.

Under the 639 Hz video, two listeners on the same tone:

this is so good

Didn't vibe right with me ,.....I must need another htz

And under 417 Hz, a note on the sound itself:

i like volume graduation

A tone that suits one person may not suit the next, and trying another is part of listening.

How do you listen to the Solfeggio frequencies?

Start with the player at the top of this page, which plays 174 Hz, the lowest of the nine. Keep the volume low and comfortable. Listen for a few minutes, then stop and notice how the room sounds without it.

To hear the whole set, the Solfeggio collection has a play button for each of the nine, free and with no ads. Each tone's page also has a Strings mode, which plays soft strings tuned to the tone's octaves, and Harmonance Studio lets you layer tones yourself. For headphones and volume, the guide to listening safely has the details, and the history of sound healing puts the Solfeggio tones among much older traditions.

Sources and limits

The 1999 book was read through its catalogue record and its publisher's own release and reply, not a printed copy. Who first added the three later tones is not recorded. Several studies were read in abstract only, and the skin conductance study's size could not be checked. The listener comments are a handful of public reactions, not evidence.

1. The Catholic Encyclopedia, Ut queant laxis: the hymn, its feast, its six notes, and the changes to UT and SI.
2. Richard Tarrant, musical settings of Horace's Odes: the translation of the first verse.
3. Dizionario Biografico degli Italiani, Guido d'Arezzo: the date of Guido's letter.
4. Sir John Hawkins, A General History of the Science and Practice of Music: Guido's method and the three days.
5. Grove's dictionary, Hexachord: syllables named steps, not notes.
6. Grove's dictionary, Pitch: early pitch, and Stuttgart's C of 528.
7. Dictionary of Scientific Biography, Joseph Sauveur: Mersenne's first estimate of a frequency.
8. BIPM, the international system of units: the hertz.
9. Nature, International Standard of Concert Pitch: the A at 440 Hz.
10. Library of Congress, the 1999 book's catalogue record.
11. Tetrahedron Publishing Group, the book's press release, archived copy.
12. Leonard G. Horowitz, reply to a review, archived copy.
13. King James Version, Numbers 7: the verse numbers.
14. Chapters and verses of the Bible: when verse numbers were added.
15. David Hulse, the Solfeggio scale frequencies, archived copy: the labels.
16. David Hulse, about the Solfeggio frequencies, archived copy: how the labels were made, and 3, 6, 9.
17. SomaEnergetics, six forks or nine, archived copy.
18. US Patent and Trademark Office, application 77099679: all nine tones listed.
19. Calamassi and Pomponi, 432 Hz and 440 Hz double-blind pilot.
20. Akimoto and colleagues, 528 Hz music in nine adults.
21. Bozok and colleagues, 528 Hz and 432 Hz music in 162 students.
22. 528 Hz sound in rats.
23. Solfeggio music in zebrafish.
24. Five Solfeggio tones, a ten-person pilot.
25. Pure Solfeggio tones and skin conductance.
26. A 417 Hz review preprint.
27. A 2026 review of music and healing frequencies.
28. A binaural beat on a 174 Hz carrier, twenty students.
29. NCCIH, Music and health.
30. Science Feedback, on the origin of the Solfeggio frequencies.
31. Robin James, the Solfeggio maths and music theory.
32. Public comments on the Harmonance videos Solfeggio scale journey, 639 Hz and 417 Hz.