The Origins of Thai Ethnic Musical Instrruments
Over time, the people who were to later become "Thai," migrated from China or perhaps further east or north into what is now northern and central Thailand somewhere very roughly estimated between 2255 B.C. and 1254 A.D. Archeologists aren't certain where exactly they migrated from but some believe that they are from the area between the Hwang-ho and Yangtze rivers. Todays' Chinese music is derived from this region. In the 6th century, Khmers settled in what is now Northern Thailand. The Khmers eventually held rulership over north and central Siam, forcing the people further south to endure the invaders rulership. In the 13th century the Thai people of Siam rose up and overthrew the Khmer.
The Thais had instruments of their own and some were from China such as the khim dulcimer, malaw cymbal and klawng jin drum. The music of India had penetrated into the Mon (southern Burma) and Khmer (Cambodia) cultures previously. Later, the Thais also came in contact with Indian music. They successfully copied many of the Indian instruments. The Thai's also created their own instruments from this interaction, namely the phin, sang, pichanai, krachappi, chakhe and thon. These are mentioned in one of the oldest books to come out of Thailand called the Tribhunikuthai and also on a stone inscription called the sila-ja rerk created during the reign of king Ramkhamhaeng who was considered the father of the nation during the Sukhothai period 1283 A.D. (Sukhothai translates as Dawn of Happiness since they overthrew the Khmer rulers). At this time they adopted some instruments such as the glawng khaek from java, the klawng malayu from Malaysia, the perng mang from the Mon people and the glawng yao from Burma.
Actually, India and Persia were already having an influence on music in China by 126 B.C. China had a book on Indian music within 5 years prior to 642. Indian music also was having an impact in Java at least by the thirteenth century, so any instruments or music borrowed from there at that time may also have been affected by India. Not much is known about Malaysian history prior to the 15th century since little was recorded except that Hinduism was having a strong presence there obviously coming from India. China records contact with Malaysia at this time and up until 1824 it was predominantly under Thai control.
The Thai tuning system is originally derived from the Javanese which in turn was derived from Chinese music theory. The Thai system is based on seven pitches an equal distance apart from each other. This results in a scale which not only does not have a perfect fifth but also has no notes which will be the same as any in the western scales. In Thai music, the fourth and seventh pitches are usually avoided, a practice similar to the avoidance of the 3rd and 7th in China. They function as ornaments or passing tones.
Thai music is in duple meter and progresses from slow, to medium to fast, similar to Indian and Korean music. Accents fall on the last beat in a group of four, the same as Korean and gamelan music of Java and Bali. The accents are played by open and closed cymbal patterns. These can be further subdivided. This relates to the rhythmic structure of gamelan music but which is played by gongs instead.
Thai music has no chords per se. The core melody is played simultaneously with its variations. They only play in unison or octaves at important points in the form then go back to playing different variations.