raŭka

One root, no seam. Raŭk- looks for a moment as though it might come apart - plenty of Esperanto words that end -ka do not, but the language has enough short roots that a learner starts hunting for them anyway. There is nothing to find here. Raŭka is a single borrowed root from Latin raucus, the -a is just the adjective ending, and there is no raŭ and no -ka suffix in Esperanto. Take it whole.

Watch the aŭ. It is a diphthong, one syllable, so raŭ-ka has two syllables and the stress falls on the first: RAŬ-ka. The ŭ is the same semivowel as in aŭto and laŭ, and it never begins a syllable of its own.

What it describes and what it does not. Raŭka is a rough, grating, worn-out voice: after shouting, after a cold, after a night of singing. It belongs to voĉo and to gorĝo, and it will happily describe a crow, a rusty hinge or a saxophone. It does not mean quiet - that is mallaŭta - and it does not mean low-pitched, which is basa. The abstract noun is raŭkeco, hoarseness, and raŭkiĝi is the verb for what happens to a football crowd by full time: to go hoarse.