Evidence No. 1: ‘It’s safer, but not completely safe.’
Murray Walker, the famous British motor racing commentator, once said in a radio interview: ‘When I consider Formula One racing now with what it was twenty years ago, it’s safer, but not completely safe.’ Click on the loudspeaker to hear all of the words he said, or click on a line to hear it on its own. (The voice is not Murray Walker’s, it’s Richard Cauldwell’s).
Interestingly, both syllables of the word 'safer' are prominent: the second syllable, containing the comparative morpheme 'er' (normally unstressed with schwa) is made both prominent and tonic (referring, fall-rise tone). Murray's choices illustrate that the desire to be absolutely clear and at the same time economic ('improving in safety' is conveyed in the one word 'safer') means that speakers can dramatically alter the sound shape of a word. Thus 'fer' becomes prominent and tonic and the vowel quality changes from schwa to the 'nurse' vowel.
For the same reasons, we might - in other contexts - expect to find similar distortions of the soundshapes of words. Click on the loudspeaker to the right, and listen to the recording. Notice that, as with 'safe' above, tone-units 07 and 09 have 'dark' and 'bright' respectively as non-prominent - these concepts are brought fully 'in play' in 06 and 08 and do not need to be made prominent in 07 and 09. For more on the meaning of prominence, see Streaming Speech Chapter 2, and Brazil (1997, chapter 2) and Brazil (1995, chapter 8).