Second Germanic sound shift

The second Germanic sound shift (zweite germanische Lautverschiebung in German), which took place during the 7th and 8th centuries, separated High German from Low German. High and Low German are separated by the Benrath line.

Under the influence of the sound shift, the unvoiced plosives p, t and k were transformed to pf or f, ts or s, and ch, respectively. Thus, the German word Straße corresponds to the English word street and the Dutch word straat. In other words, Straße is one of the High German words that formed during the time when the second Germanic sound shift took place while the forms street and straat are relics of the Low German languages of which Anglo-Saxon, later Old English, and Old Dutch were part.

Some of the phonemes (specifically, /pf/, /ts/, and in Swiss German /kx/) created by the second sound shift are known as affricates, a combination of a plosive plus a fricative; in particular. the affricate [pf] is phonetically quite rare among the languages of the world.