I'm not clear how is the input features are stacked in wakeword applications. Taking https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/43969.pdf as an example, the author mentioned that
First, in the feature extraction module, 40 dimensional log-mel filterbank features are computed every 25ms with a 10ms frame shift. Next, at every frame, we stack 23 frames to the left and 8 frames to the right, and input this into the DNN.
So, given a one second audio, sample rate: 16000, frame length: 25ms, frame shift: 10ms and mel bins: 40. We can have a feature with the shape of [98, 40], where 98 is the number of frames.
How can we stack this feature? Thanks