Patent ID: 7259700

Claim:
A method of converting sampling frequency according to a predetermined ratio comprising a first initialisation stage consisting in acquiring a first sampling frequency, called Fsin, associated with a first digital signal, called an input signal, and in selecting a second sampling frequency, called Fsout, called an output signal, wherein the ratio between the said first and second sampling frequencies constitute the said predetermined ratio, said method comprising an initialisation phase that includes: a first initialisation stage consisting in determining a single whole number k, so that the relation: (Fsin/Fsout)/2 k >1≧(Fsin/Fsout)/(2 (k+1) ) is satisfied, and in recording the said number in storage means; a second initialisation stage consisting, if k>0, in configuring a digital filter for under-sampling the said input signal by a factor 2 k , and in recording the parameters associated with this configuration in storage means; a third initialisation stage consisting in configuring a digital band-pass limiting filter with a cut-off frequency Fsout/2 and in determining its coefficients if, and only if one of the following relations is satisfied: Fsin≦Fsout, Fsin>Fsout≧Fsin/2 or Fsin/2<Fsout, and in recording the said coefficients in storage means; and a process phase carried out in real time, comprising: a first process stage consisting, if and only if k>0, in applying the said digital under-sampling filter by a factor 2 k to the said input signal so as to generate an intermediate signal; a second process stage consisting, if and only if k≧0, in applying the said digital band-pass limiting filter to the said first intermediate signal, and in short-circuiting this filter if k<0, so as to generate a second intermediate signal; a third process stage consisting in over-sampling the said second intermediate signal by a predetermined factor L; and a fourth process stage consisting in applying to the said third signal a stage for interpolating digital data so as to generate the said output signal at the sampling frequency Fsout.