The Couriers is an a cappella setting of Sylvia Plath's short poem by the same name. The music was originally written 1997 and intended for a human choir. However, after discovering the programming interface to the voice synthesizer built in to Apple's OS-X, I thought it would be an interesting experiment and a great test of the state of the art to try to synthesize all the parts instead. This is the result, as recorded in November 2013:
The Apple Speech Synthesis API is still quite primitive, and was in any case designed for speech synthesis, not synthesis of the singing voice. In normal use, the programmer would hand the synthesizer a line of text — something like "Press the button to start" — which the synthesizer would then render as best it is able, without any further guidance from the programmer. However, the synthesizer also supports an input mode called TUNE which allows the programmer to specify the duration and frequency of every portion of the text, including the duration of silences between words. The only caveat is that the text must be broken down and rewritten as a sequence of phonemes, since duration and frequency may only be specified on the phonemic level.
As one might imagine, the resulting script is cumbersome, arcane, and bears no resemblance to a musical score. The high-level symbolism and efficiency of musical notation is entirely lacking. This is the soprano part to the short fragment "talking and crackling", rewritten in Apple's ASCII phonetic symbols as "tAOkIYN AEnd krAEklIYN":
In this script, the percent sign is used to notate silence. The characters +, ~ and _ notate different levels of syllabic stress (similar to poetic scansion). Duration (D) is in milliseconds, and pitch (P) is in cycles per second (Hz). Volume changes are notated with the "volm" directive. The Speech Synthesis API provides a number of different voices, but only a few of the voices work in TUNE mode. The voice called "Junior" was found to have the best all-round characteristics for the present purpose.
Speaking of Sylvia Plath, this is a setting of her poem Elm composed in 1997, as performed by mezzo-soprano Catherine Treadgold and violist Scott Ligocki: