An apparatus for analysing the condition of a machine having a part rotating with a variable speed of rotation (f ROT), comprising: a first sensor adapted to generate an analogue measurement signal (S EA) dependent on mechanical vibrations (V MD) emanating from rotation of said part; an analogue-to-digital converter adapted to sample said analogue measurement signal at an input sampling frequency (fs) so as to generate a digital measurement signal (S MD) in response to said analogue measurement signal (S EA); a digital filter adapted to receive said digital measurement signal (S MD) and to deliver a filtered digital signal (S F) dependent on said digital measurement signal (S MD); a digital enveloper adapted to generate a digitally enveloped signal (S ENV) dependent on said filtered digital signal (S F); a first decimator adapted to perform a decimation of the digitally enveloped signal (S ENV) so as to achieve a first decimated digital signal (S RED1, S ENV) having a first reduced sampling frequency such that the first reduced sampling frequency is reduced by an integer factor as compared to the input sampling frequency (fS); a second decimator (470, 470A, 470B), and an evaluator (230, 290, 294) adapted to perform a condition analysis function (F 1, F2, Fn) for analysing the condition of the machine; characterized by said second decimator (470, 470A, 470B) having a first input for receiving said first decimated digital signal (S RED1, S ENV), and a second input for receiving a signal indicative of said variable speed of rotation (f ROT) associated with said rotating part; a third input for receiving a signal indicative of an output sample rate setting signal; and by said second decimator (470, 470A, 470B) being a fractional decimator adapted to generate a second digital signal (S RED2) having an output sample rate (f SR2) such that the number of sample values per revolution of said rotating part is kept at a substantially constant value; said second decimator (470, 470A, 470B) generating said second digital signal (S RED2) in response to said first decimated digital signal (S RED1, S ENV), said signal indicative of said variable speed of rotation (f ROT); and said signal indicative of an output sample rate setting signal; and by said evaluator (230, 290, 294) being adapted to perform said condition analysis function (F1, F2, Fn) dependent on said second digital signal (S RED2). a first sensor adapted to generate an analogue measurement signal (S EA) dependent on mechanical vibrations (V MD) emanating from rotation of said part; an analogue-to-digital converter adapted to sample said analogue measurement signal at an input sampling frequency (fs) so as to generate a digital measurement signal (S MD) in response to said analogue measurement signal (S EA); a digital filter adapted to receive said digital measurement signal (S MD) and to deliver a filtered digital signal (S F) dependent on said digital measurement signal (S MD); a digital enveloper adapted to generate a digitally enveloped signal (S ENV) dependent on said filtered digital signal (S F); a first decimator adapted to perform a decimation of the digitally enveloped signal (S ENV) so as to achieve a first decimated digital signal (S RED1, S ENV) having a first reduced sampling frequency such that the first reduced sampling frequency is reduced by an integer factor as compared to the input sampling frequency (fS); a second decimator (470, 470A, 470B), and an evaluator (230, 290, 294) adapted to perform a condition analysis function (F 1, F2, Fn) for analysing the condition of the machine; said second decimator (470, 470A, 470B) having a first input for receiving said first decimated digital signal (S RED1, S ENV), and a second input for receiving a signal indicative of said variable speed of rotation (f ROT) associated with said rotating part; a third input for receiving a signal indicative of an output sample rate setting signal; and by a first input for receiving said first decimated digital signal (S RED1, S ENV), and a second input for receiving a signal indicative of said variable speed of rotation (f ROT) associated with said rotating part; a third input for receiving a signal indicative of an output sample rate setting signal; and by said second decimator (470, 470A, 470B) being a fractional decimator adapted to generate a second digital signal (S RED2) having an output sample rate (f SR2) such that the number of sample values per revolution of said rotating part is kept at a substantially constant value; said second decimator (470, 470A, 470B) generating said second digital signal (S RED2) in response to said first decimated digital signal (S RED1, S ENV), said signal indicative of said variable speed of rotation (f ROT); and said signal indicative of an output sample rate setting signal; and by said first decimated digital signal (S RED1, S ENV), said signal indicative of said variable speed of rotation (f ROT); and said signal indicative of an output sample rate setting signal; and by said evaluator (230, 290, 294) being adapted to perform said condition analysis function (F1, F2, Fn) dependent on said second digital signal (S RED2).