This paper presents a new approach to estimating the speech spectral envelope that is adapted for Voice Conversion (VC). In particular, we represent the spectral envelope as a sum of peaks that evolve smoothly in time, within a phoneme. We highlight important properties of our proposed spectral envelope estimation and illustrate its potential for use in a VC context. We analyse natural speech using the proposed methods and we compare results with those from a more traditional frame-by-frame cepstrum-based analysis. Subjective comparisons of synthesized speech quality, as well as implications of this work in future research are also discussed.