Improved Patch-Mix Transformer and Contrastive Learning Method for Sound Classification in Noisy Environments

In urban environments, noise significantly impacts daily life and presents challenges for Environmental Sound Classification (ESC). The structural influence of urban noise on audio signals complicates feature extraction and audio classification for environmental sound classification methods. To address these challenges, this paper proposes a Contrastive Learning-based Audio Spectrogram Transformer (CL-Transformer) that incorporates a Patch-Mix mechanism and adaptive contrastive learning strategies while simultaneously improving and utilizing adaptive data augmentation techniques for model training. Firstly, a combination of data augmentation techniques is introduced to enrich environmental sounds. Then, the Patch-Mix feature fusion scheme randomly mixes patches of the enhanced and noisy spectrograms during the Transformer's patch embedding. Furthermore, a novel contrastive learning scheme is introduced to quantify loss and improve model performance, synergizing well with the Transformer model. Finally, experiments on the ESC-50 and UrbanSound8K public datasets achieved accuracies of 97.75% and 92.95%, respectively. To simulate the impact of noise in real urban environments, the model is evaluated using the UrbanSound8K dataset with added background noise at different signal-to-noise ratios (SNR). Experimental results demonstrate that the proposed framework performs well in noisy environments.