This is a good idea and quite successful. The program enables the Spectrum to 'speak', enabling a vocabulary of 46 pre-defined words to be stored above Ramtop.
This set includes all whole numbers, plus a vocabulary derived from Star Trek, including words like "phasor" and "starbase" as well as some colours and directions.
Also included is the "s" sound to pluralise many words. Clever programmers might also be able to split words by altering the addresses of the stored data, for example to get "speed" from "s" and "torpedo".
The quality of the sound is surprisingly good, though it takes a bit of getting used to. But there is a great deal of background fuzz, and amplifying the output sometimes seems to amplify the fuzz at the expense of the speech.
It takes two lines of program to produce a word, but long utterances can easily be programmed. However very few long sentences are possible with the vocabulary provided. Most applications will be simple single word warnings or hints in games programs.
Certainly not as good as most speech chips, but quite a remarkable manipulation of the Spectrum's primitive sound system.