Pushing the Limit of Sound Event Detection with Multi-Dilated Frequency Dynamic Convolution

Frequency dynamic convolution (FDY conv) has been a milestone in the sound event detection (SED) field, but it involves a substantial increase in model size due to multiple basis kernels. In this work, we propose partial frequency dynamic convolution (PFD conv), which concatenates outputs by conventional 2D convolution and FDY conv as static and dynamic branches respectively. PFD-CRNN with proportion of dynamic branch output as one eighth reduces 51.9% of parameters from FDY-CRNN while retaining the performance. Additionally, we propose multi-dilated frequency dynamic convolution (MDFD conv), which integrates multiple dilated frequency dynamic convolution (DFD conv) branches with different dilation size sets and a static branch within a single convolution layer. Resulting best MDFD-CRNN with five non-dilated FDY Conv branches, three differently dilated DFD Conv branches and a static branch achieved 3.17% improvement in polyphonic sound detection score (PSDS) over FDY conv without class-wise median filter. Application of sound event bounding box as post processing on best MDFD-CRNN achieved true PSDS1 of 0.485, which is the state-of-the-art score in DESED dataset without external dataset or pretrained model. From the results of extensive ablation studies, we discovered that not only multiple dynamic branches but also specific proportion of static branch helps SED. In addition, non-dilated dynamic branches are necessary in addition to dilated dynamic branches in order to obtain optimal SED performance. The results and discussions on ablation studies further enhance understanding and usability of FDY conv variants.