2427959-A cites 2 patents.
The Acoli language has 4 types of tones called voices and 3 combinations of tones. These voices and combinations fall under two categories, group A and group B. With group A the vowels are pronounced from the throat. With group B the vowels are pronounced from the chest and they are louder than group A vowels. An orthography is defined combining vowels of the Latin alphabet with diacritical marks to indicate the appropriate pronunciation.