The most popular forms in Arab music have their roots in the Ottoman period, and their names are often Arabic versions of the original Turkish (e.g. Arabic bashraf from Turkish pesrev). In fact, most of the well-known pieces in the Arab classical repertoire were written by Ottoman composers, and the most famous pieces are referred to using the composer's name, e.g. Sama'i Tatyos (after Tatyos Efendi). Since the end of Ottoman rule these pieces have remained popular throughout the Arab world, although Arab musicians often perform them quite differently to their Turkish counterparts. The most frequently encountered instrumental forms are described below.
The Arab sama'i is equivalent to the Turkish saz semai, and is made up of four sections called khanat (sing. khana), each of which is followed by a refrain (taslim). The first three khanat are in the samai thaqil rhythm (10/8) and the fourth is in samai darij (3/4 or 6/8), although each taslim remains in samai thaqil rhythm. A samai will be based on a particular maqam, and the melodic progression of the piece will follow loosely the sayr of the maqam. The melody will begin in the 'home' maqam for the first khana, introduce modulation to related maqamat in the second khana, move to the upper register of the scale in the third khana, and then return to the initial theme in the final khana.
As mentioned above, the Arab bashraf derives from the Turkish pesrev. The bashraf is very similar in structure to the samai and also consists of four khanat, each followed by a taslim. The main difference is that the rhythmic structure of the bashraf is generally more complex (with a rhythmic grouping in 'twos' rather than a mixture of 'twos' and 'threes') and the same rhythm is preserved throughout the piece. As with the samai, the bashraf is based on a particular maqam and its melody follows the sayr of that maqam (including modulations).
The longa is an instrumental form in a 2/4 rhythm consisting of several khanat, each followed by a taslim. Note, however, that the last khana is normally in a 3/4 rhythm, as in the case of a samai.
The tahmilah is an insrumental piece made up of alternating sections played by the ensemble and solo instruments. The parts played by the ensemble are relatively fixed compositions, whereas the solo parts are mostly improvised, providing plenty of room for individual expression.
This is a short instrumental prelude, normally performed in unison by an ensemble, with the aim of presenting the basic outline of a particular maqam before subsequent elaboration in a longer picece of music.
The taqsim is a semi-improvised form (usually without rhythmic accompaniment) that demonstrates perfectly the structure of a particular maqam and its relation to similar maqamat. Its performance is a highly skilled art and relies on an intimate knowledge of the structure of the different maqamat and the relationships between them. During a taqsim the performer will follow the general sayr of the maqam, emphasising important tones and using key melodic phrases, and will usually modulate to several related maqamat before returning to the original maqam.
[Note: For more detailed information on a wide range of instrumental and vocal forms in Arab music, including those listed above, visit the comprehensive Arabic Maqam World website.]