For decades, speech recognition relied on HMMs with Gaussian mixtures. Around 2010–2012, teams at Toronto, Microsoft, Google, and IBM showed DNNs substantially improved acoustics.
The shift was among the first mass industrial deployments of deep learning, even before AlexNet’s fame among the broader technical public.
Today speech is dominated by end-to-end and multimodal models, but the HMM→DNN bridge was a critical rung of enterprise trust in deep nets.