"Winter" has a very, um, seasonal flavor to it. Its sounds try both to convey an idea of "winter" but also the idea of changing seasons more generally. As far as giving us an idea of what "winter" sounds like, consider the poem's use of onomatopoeia in several instances. Twice the speaker attempts to imitate the owl's song ("Tu-whit, tu-who!"), a song that, in this poem, symbolizes winter. If the owl's song is an outdoor, wintry sound, the "hiss" (another onomatopoetic sound) is a wintry, indoor sound—the sound of a certain food-beverage (roasted crab apples in ale) consumed when it's cold outside.
While these are the most "wintry" sounding moments of the poem, there are other, more subtle moments where the sounds of winter take over. Consider the long O sound in a word like "frozen" (4); it shows up all over the poem ("home," "Joan," "nose," "blow"). The repetition of the key vowel sound of "frozen," a word that might as well be synonymous with winter, is yet another way in which the poem sonically renders the idea of winter.
The repetition, or assonance, of the long O in this poem, however, is by no means the only instance of repetition. The last three lines of each stanza (the refrain) are the same (a fact that tells us this poem is also a song), and the speaker often uses anaphora (with the repetition of the same word at the beginning of successive lines). All the monotonous repetition points to the monotony of winter. Cold, ice, snow—yup, it's all pretty much the same until the spring arrives.
The repetition also, however, gives us an idea of the cycles of the seasons. The refrain, for example, appears in the same place in each stanza, in much the same way that winter appears at about the same time every year. The same goes for the other forms of repetition like anaphora—they give the poem's sounds a sameness that mimics the sameness or regularity of the seasons, of which winter is one (and seasons are important when you consider that "Winter" is paired with "Spring" in Love's Labour's Lost). Pretty nifty, eh?