A system and method of estimating metric values from digital samples of received communications signal carrying symbols modulated in a selected first modulation format and symbols modulated in a second modulation format. The selected first modulation format can be selected from among multiple supported first modulation formats. The system can receive the digital samples in sample blocks a plurality of which constitute a data frame. Each sample block can comprise a first region that contains first samples corresponding to the selected first modulation format or overhead samples regardless of the selected first modulator format or an index of the sample block in the frame; a second region that contains second samples corresponding to a second modulation format regardless of the selected first modulator format or an index of the sample block in the frame; and a third region in which whether the samples are first samples or second samples depends on the selected first modulation format or the index of the sample block in the frame. The system estimates first metrics according to the selected first modulation format for each of the first samples and second metrics according to the second modulation format for each of the second samples. The system also estimates both first metrics and second metrics for each of the third samples and then selects valid ones of the first metrics and second metrics for the third samples in accordance with the selected first modulation format or the index of the sample block in the frame.