0.9 Sampling rate conversion

Sampling rate conversion

In general, sampling rates are converted only in rational fractions such as from 32 to 48 kHz by a factor of 3/2 which are performed byappropriate sequences of up- and down-sampling.

Practical considerations:

• First interpolate, then decimate (preserve signal quality)
• the low-pass filters used after upsampling (2nd step of interpolation) and before downsampling (1st step of decimation)can be combined into the one filter with the smaller pass-band.
• Interpolation and Decimation by large factors should be done in steps, keeping $N$ and $M$ below or at 6 at most.
• Matlab commands: decimate , downsample , interp , upsample , resample . See the corresponding help manual ( help decimate etc).
• The ideal sinc filter is not realizable since it requires knowledge of the infinite past and future; one uses FIR filters with linearphase to avoid audible artifacts.