Tone terracing is a type of phonetic downdrift, where certain tones shift downward in pitch after other tones. The result is that a tone may be realized at a certain pitch over a short stretch of speech, shift downward and then continue at its new level, then shift downward again, until the end of the prosodic contour is reached, and the pitches reset. A graph of the change in pitch over time of a particular tone resembles a terrace. Phonetics (from the Greek word φωνή, phone = sound/voice) is the study of sounds (voice). ... Downdrift is a linguistic phenomenon defined as the lowering of high tones that are separated by low tones. ... It has been suggested that Tonal language be merged into this article or section. ... Prosody may mean several things: Prosody consists of distinctive variations of stress, tone, and timing in spoken language. ... Terraced vineyards near Lausanne The Incan terraces at Písac are still used today. ...

Tone terracing is particularly common in the languages of West Africa.  Western Africa (UN subregion)  Maghreb West Africa or Western Africa is the westernmost region of the African continent. ...

Two basic types of tone terracing are found. In one, all tones shift downward, so that their difference in pitch remains constant; in the other, the pitch of the low tone remains at the lower end of the speaker's vocal range, while the other tones shift downward, so that their difference in pitch narrows. Pitch reset is required in the first instance because the tones approach the lower end of the speaker's comfort range, and in the second because the tonal distinctions of the language start being lost.

It is very common for only the low tone to cause a downstep in pitch, whether the result is that all tones, including subsequent low tones, are terraced, or whether only non-low tones are. Downstep is a phonemic or phonetic downward shift of tone between the syllables or words of a tonal language. ...

A somewhat more intricate system is found in the Twi language of Ghana. Twi has three phonemic tones: high, mid, and low. A word, and therefore a prosodic chunk of speech, may only start with a high tone or a low tone on its first syllable. As in many languages, a low tone starts out and remains at the bottom of the speaker's range. After a low tone, a subsequent high tone is downstepped. (A temporary exception occurs when a single low tone is found between two high tones. In this case the low tone is raised from its base value, but the second high tone is still downstepped, and subsequent low tones return to the base pitch.) Twi (pronounced chwee) is a language spoken in Ghana by about 6 million people. ...

However, a phonetic downstep occurs between any two adjacent mid tones as well. In fact, a high tone is defined as any tone that is at the same pitch as a preceding high or mid tone; a mid tone will always be lower in pitch than a preceding high or mid tone. The result is that every instance of a mid or low tone shifts the upper end of the pitch range downward, until all pitches are reset at the end of the prosodic melody.

Table 1. The phonetic terracing effect in Twi of a series of mid tones. (The first tone must be either high or low.)

Table 2. The phonetic terracing effect in Twi of an alternating series of high and mid tones.

Table 3. The phonetic terracing effect in Twi of an alternating series of high and low tones.

From tables 2 and 3 it can be imagined that the tone sequences high-low-high and high-mid-high may be difficult for a non-native speaker to distinguish.

Bibilography

• J.E. Redden and N. Owusu (1963, 1995). Twi Basic Course. Foreign Service Institute (Hippocrene reprint). ISBN 0-7818-0394-2