“How does timbre work into advanced heterophony concepts?” In the twentieth century, The Radshidiyya Institute in Tunis looked to expand the ma’luf.
[Ma’luf] is characterized by small, solo instrumental ensembles, traditionally made up of a rabab… which may be replaced by a violin… an ud… [a] naqqarat… and tar. (The Garland Encyclopedia of World Music: The Middle East Ruth Davis 327)
The leader of the ensemble, called a shaykh, had been chosen for his depth of musical knowledge.
The shaykh… provided the authoritative rendering for the chorus. Within this framework, however, each soloist interpreted the melodies in his own individual way, embellishing them spontaneously… The result was a heterophonic texture. (327)
The Radshidiyya expanded the ma’luf by adding more instruments. The best shaykhs joined, and they had an ensemble that included:
…six violins, two [rababs], five [uds], three qawanin, a tar and a naqqarat, as well as six male vocalists and one female vocalist. (327)
The experiment failed. Ruth Davis explains:
Such an ensemble was unprecedented, not only in the size and variety of its instruments but, more critically, in that it combined several instruments of the same type. As several shaykhs, unaccustomed to performing together, struggled against one another’s versions of the melodies, heterophony turned into cacophony. (327)
To Western ears, ethnic bowed string instruments can have a nasal sound. However, listeners must be careful not to assume that the instrument makers created inferior instruments. In fact, a large part of the string tone comes from the playing technique.
Because the bow is applied near the bridge, the rebab has a more nasal quality than the violin. (Sethares 210)
For heterophony to work the different versions of the melody must be performed on instruments with different timbres or the heterophony turns into a mess.