A digital modulator having a sample rate converter that does not require that the final output sampling rate, FOUT, of the sample rate converter be at least twice as great as the input sampling rate, FIN, of the sample rate converter. The upsampling interpolation filter stages of the sample rate converter of the invention do not require any reference clocks to be provided by the NCO of the sample rate converter. Therefore, the upsampling interpolation filter stages are decoupled from the final output sampling rate, FOUT. The interpolation algorithms may be implemented in software, hardware, or a combination of software and hardware. In addition, the polynomial-based interpolator of the Farrow Structure of the invention is capable of using an even or odd number of basepoints.