Tone letter

A series of iconic tone letters based on a musical staff was devised by Yuen Ren Chao in the 1920s[2] by adding a reference stave to the existing convention of the International Phonetic Alphabet.

[3] When the contours had been drawn without a staff, it was difficult to discern subtle distinction in pitch.

Only nine or so of the possible tones were commonly distinguished: high, medium and low level, [ˉa ˗a ˍa] (or as dots rather than macrons for 'unaccented' tones); high rising and falling, [ˊa ˋa]; low rising and falling, [ˏa ˎa]; and peaking and dipping, [ˆa ˇa], though more precise notation was found and the IPA specifically provided for mid rising and falling tones if needed.

[4] The Chao tone letters were originally x-height, but are now taller to make distinctions in pitch more visible.

For example, [ma˨˩˦] represents the mid-dipping pitch contour of the Chinese word for horse, 馬／马 mǎ.

Single tone letters differentiate up to five pitch levels: ˥ 'extra high' or 'top', ˦ 'high', ˧ 'mid', ˨ 'low', and ˩ 'extra low' or 'bottom'.

[9] The phonetic realization of neutral tones are sometimes indicated by replacing the horizontal stroke with a dot: ⟨꜌ ꜋ ꜊ ꜉ ꜈⟩.

This is an extension of the pre-Kiel IPA convention of a dot placed at various heights to indicate the pitch of a reduced tone.

Until the spread of OpenType computer fonts starting in 2000–2001, tone letters were not practical for many applications.

Conversely, in Africa the lowest pitch is assigned a 5 and the highest a 1, barring a few exceptional cases with six tone levels, which may have the opposite convention of 1 being low and 6 being high.

For example, an Otomanguean language with three level tones may denote them as 1 (high /˥/), 2 (mid /˧/) and 3 (low /˩/).

The International Phonetic Association suggests using the tone letters to represent phonemic contrasts.

The Hmong Romanized Popular Alphabet was devised in the early 1950s with Latin tone letters.

A unified Miao alphabet used in China applies a different scheme: In Highland Chatino, superscript capital A–L, ᴬ ᴮ ꟲ ᴰ ᴱ ꟳ ᴳ ᴴ ᴵ ᴶ ᴷ ᴸ, indicate pan-dialectical tone-cognate sets.

Ozumacín Chinantec uses the following diacritics: Sample: Jnäꜘ Paaˊ naˉhña̱a̱nˊ la̱a̱nˈ apóstol kya̱a̱ꜗ Jesucristo läꜙ hyohˉ dsëꜗ Dio.

The related Lahu and Akha use the following spacing diacritic marks, which occur at the end of a syllable.