Abstract Lombard and Clear speech represent two acoustically and perceptually distinct speaking styles that humans employ, depending on context, in order to increase intelligibility. In particular, increased spectral energy in a band spanning the range of formants is consistently observed for Lombard speech, effectively augmenting loudness, while vowel space expansion is exhibited in Clear speech, representing greater articulation and vowel discrimination. Though these two acoustic phenomena are largely attributed with the re- spective intelligibility gains of the styles, the analyses illustrated in this work would suggest that they are mutually exclusive in human speech pro- duction. Signal processing algorithms, on the other hand, can achieve both feats simultaneously. In the case of Lombard speech, augmenting spectral energy in a formant band is a relatively straightforward modification that is currently exploited in many algorithms that successfully increase intelligi- bility. Conversely, the vowel space expansion exhibited by Clear speech is a more challenging phenomena to address and is consequently rarely explored. For this reason, the modifications examined in this work focus especially on this latter task. Specifically, a novel Clear speech-inspired frequency warp- ing technique is presented and shown to achieve vowel space expansion. The frequency warping is then incorporated into an established Spectral Shaping method that mimics Lombard spectral gains and that also pairs with Dy- namic Range Compression to maximize speech audibility (SSDRC). In the end, objective and subjective evaluations are presented in order to assess and compare the intelligibility gains of the different styles and modifications.