In this paper, we consider nonconvex minimax optimization, which is gaining prominence in many modern machine learning applications, such as GANs. Large-scale edge-based collection of training data in these applications calls for communication-efficient distributed optimization algorithms, such as those used in federated learning, to process the data. In this paper, we analyze local stochastic gradient descent ascent (SGDA), the local-update version of the SGDA algorithm. SGDA is the core algorithm used in minimax optimization, but it is not well-understood in a distributed setting. We prove that Local SGDA has order-optimal sample complexity for several classes of nonconvex-concave and nonconvex-nonconcave minimax problems, and also enjoys linear speedup with respect to the number of clients. We provide a novel and tighter analysis, which improves the convergence and communication guarantees in the existing literature. For nonconvex-PL and nonconvex-one-point-concave functions, we improve the existing complexity results for centralized minimax problems. Furthermore, we propose a momentum-based local-update algorithm, which has the same convergence guarantees, but outperforms Local SGDA as demonstrated in our experiments.

We describe a learnable modulation spectrogram feature for speech activity detection (SAD). Modulation features capture the temporal dynamics of each frequency subband. We compute learnable modulation spectrogram features by first calculating the log-mel spectrogram. Next, we filter each frequency subband with a bandpass filter that contains a learnable center frequency. The resulting SAD system was evaluated on the Fearless Steps Phase-04 SAD challenge. Experimental results showed that temporal modulations around the 4–6 Hz range are crucial for deep-learning-based SAD. These experimental results align with previous studies that found slow temporal modulation to be most important for speech-processing tasks and speech intelligibility. Additionally, we found that the learnable modulation spectrogram feature outperforms both the standard log-mel and fixed modulation spectrogram features on the Fearless Steps Phase-04 SAD test set.