CNN-n-GRU: end-to-end speech emotion recognition from raw waveform signal using CNNs and gated recurrent unit networks

We present CNN-n-GRU, a new end-to-end (E2E) architecture built of an n-layer convolutional neural network (CNN) followed sequentially by an n-layer Gated Recurrent Unit (GRU) for speech emotion recognition. CNNs and RNNs both exhibited promising outcomes when fed raw waveform voice inputs. This inspired our idea to combine them into a single model to maximise their potential. Instead of using handcrafted features or spectrograms, we train CNNs to recognise low-level speech representations from raw waveform, which allows the network to capture relevant narrow-band emotion characteristics. On the other hand, RNNs (GRUs in our case) can learn temporal characteristics, allowing the network to better capture the signal’s time-distributed features. Because a CNN can generate multiple levels of representation abstraction, we exploit early layers to extract high-level features, then to supply the appropriate input to subsequent RNN layers in order to aggregate long-term dependencies. By taking advantage of both CNNs and GRUs in a single model, the proposed architecture has important advantages over other models from the literature. The proposed model was evaluated using the TESS dataset and compared to state-of-the-art methods. Our experimental results demonstrate that the proposed model is more accurate than traditional classification approaches for speech emotion recognition.