Ladefoged & Maddieson (1996) note that there is "a complication in the case of uvular fricatives in that the shape of the vocal tract may be such that the uvula vibrates."

Although they are not normally differentiated in study, languages in which they have been (Hebrew, Wolof, as well as the northern and central varieties of European Spanish) have been found to specifically possess the fricative trill.

It is found as either the fortis counterpart of /ɣ/ (which itself is voiceless at least in Northern Standard Dutch: [x]) or the sole dorsal fricative in Northern SD and regional dialects and languages of the Netherlands (Dutch Low Saxon and West Frisian) spoken above the rivers Rhine, Meuse and Waal (sometimes termed the Rotterdam–Nijmegen Line).

A plain fricative that is articulated slightly further front, as either medio-velar or post-palatal is typical of dialects spoken south of the rivers (mainly Brabantian and Limburgish but excluding Ripuarian and the dialect of Bergen op Zoom), including Belgian SD.

This is the case in Northern Standard Dutch as well as some varieties of Arabic, Limburgish and Madrid Spanish.