In OE the fricatives f, s, Þ were subjected (подверглись) to a process of voicing and devoicing. They became voiced intervocally – between vowels, sonorants and voiced consonants. In other positions they remained voiceless.
weorÞan – (становиться) [ð],
wearÞ (стал) - [θ]
Palatalization
The velar consonants [k, g, g:, х] were palatalized before a front vowel and approached (приближаться) affricates in Late OE.
k>k’>ʧ cild ‘child’
sk>sk’>ʃ scip ‘ship’
g(g:)>g’(g:’)>dʒ senʒean ‘singe’
brycʒ ‘bridge’
Assimilation
Assimilation is a process when two adjacent consonants within a word influence each other in such a way that the articulation of one sound becomes similar to or identical with the articulation of the other one.