a method that uses time - domain processing on a spectrally efficient digital modulation scheme to reduce the bandwidth expansion in envelope elimination and restoration amplifiers is disclosed . the method identifies and localizes sections of the signal responsible for the out of band emissions , or spectral regrowth , using a filter . the detected sections are flagged and extended to allow for introduction of a lower frequency transition in place of the extended section , thus reducing spectral regrowth from the output of an eer amplifier . the method is particularly useful for improving the quality of digital am radio transmission .