Time-stretched (-expanded or -slowed, versus, after “negative stretching”, sped-up or “compressed”) audio is of obvious benefit to language learners during listen comprehension skill training exercises, as well as other audio-lingual activities (commonly associated with non- or virtual (online) “language labs”) and an affordance of digital audio media.
As well as compressed audio, especially for repetitive audio-lingual exercises, beyond the obvious possibility of fitting more content into the same time frame since “listeners can process at a much higher rate than normal conversational speech, with some loss of comprehension” (see Roby (1996), Auditory Presentations and Language Laboratories. Handbook of Research on Educational Communications and Technology, 821-850).
Roby, W.B. (2004). Technology in the service of foreign language teaching: The case of the language laboratory. In D. Jonassen (ed.), Handbook of Research on Educational Communications and Technology, 523-541, 2nd ed., 526f. summarizes language learning applications of the “technical advance [of the] speech compressor–expander. This device allowed a recording to be sped up(com-pressed) or slowed down (expanded). Articles on this technology were numerous in the general educational literature from the start of the decade. Sanford Couch (1973),a professor of Russian, advocated its use. Paradoxically, it was not until 1978 that anything on speech compression appeared in the NALLD Journal (Harvey, 978). One would have expected a greater enthusiasm for this feature among language laboratory professionals. The ability to slow down a tape would seem to be a boon to students struggling with a difficult passage. Moreover, variable speed technology was not unknown in foreign-language / teaching, for Hirsch 1954) had commended the use of the soundstretcher (p.22) in the early 1950s. “
The application pictured above simplifies common audio-material producing tasks involving slowing or speeding up (or both) digital audio, with a twist: It allows for pauses being stretched more than non-pauses, thus remediating the common disadvantage of common time stretching applications that – even though pitch is now routinely maintained when altering the speed of digital audio – the result can remind one of drunk speak.
I hope this will help you use more of the many authentic foreign language audio materials available free on the internet.