hi cpu usage at 1.5x

[gestapo]

hi,
why there is a huge cpu usage difference between dd 1.4x and dd 1.5x. i mean dd 1.4i uses 10% or 15% cpu at my system. but dd 1.5a, 1.5b or 1.5c uses about 65% cpu. i tried several codec combinations but no chance. there isnt any other program uses increases cpu usage.

any idea?