"Learning vocabulary in your sleep" sounds like an empty promise – but it is partly backed by science. What matters is what exactly you mean by it: the sleeping brain cannot absorb new knowledge from scratch. But it can do something at least as valuable: consolidate what was learned before.
During deep sleep, the brain replays activity patterns from the day – a process researchers call memory consolidation. Material learned shortly before falling asleep is preferentially transferred from short-term to long-term memory. Studies from the universities of Zurich and Bern also showed that replaying previously learned vocabulary during certain sleep phases can improve recall the next day.
This leads to a simple, effective routine: first learn the words while awake – for example with the vocabulary trainer or a learning video. Then, while falling asleep, listen to an audiobook containing exactly those words. Repetition in a relaxed state and the subsequent consolidation during sleep work hand in hand.
That is exactly what the 1000 Words audiobooks with triple repetition are made for: every word pair is spoken three times in a row – first in your native language, then in the target language. The pace is deliberately calm, without music and without abrupt changes, so you can fall asleep to it.
One thing remains important: sleep does not replace active learning, it amplifies it. If you only listen passively and never practice actively, you will hardly make progress. The combination makes the difference – short active sessions with spaced repetition during the day, listening repetition in the evening. That way you use both systems of your memory optimally.