Fractional Resampler - GNU Radio
&quot;Phase shift&quot; is poor terminology as time delay is not exactly the same, but the significance of the 0 to 1 factor is a fractional delay in units of samples.
The filter itself will always have additional delay, as a causal filter which is simply a processing delay independent of resampled delay as given by the phase shift parameter. For example a resampling delay of 0.5 will resample the original waveform such as to provide all new samples that are midway in between the current samples, and this new resampled waveform will be completely delayed by the filtering delay in time related to the input waveform.
The example in the figure below shows the original samples as blue dots of an underlying continuous time waveform as the line. If we used a &quot;phase shift&quot; parameter of 0.2, the samples as given by the red dots would be determined as the interpolated fractional delay values. These red dots would all be shifted even further to the right relative the original locations as shown in the lower plot due to the processing delay of the filter itself. (As we would see with any causal filter).