Whispering changes the sound of speech
A whisper is not simply ordinary speech turned down. In normal speech, the vocal folds vibrate, giving vowels a strong, patterned sound. In a whisper, they usually do not vibrate; air passes through the throat as noise instead. The result has less of the clear harmonic structure and pitch information that speech-recognition systems can use to distinguish sounds.
Whispering also tends to soften or reshape parts of words. Vowels may be less distinct, and consonants can blend into the breathy sound. That leaves a recognition system with a less familiar acoustic pattern to match to words.
Quiet rooms and distant microphones make it harder
Assistants are generally built to recognize speech across many voices and settings, but their recognition models and microphone-processing systems are typically tuned around ordinary spoken voices. A quiet whisper may fall below the level that a device’s voice detector expects, especially when the speaker is across a room. If background noise is present, it can mask the faint speech before the assistant has a chance to interpret it.
So the problem is not that the assistant cannot hear a whisper at all. It is that whispering changes both the sound pattern and the signal strength, making the words harder to separate from noise and identify. Speaking at a normal, clear volume gives the microphones and recognition system a cleaner signal to work with.
