De-crackling Virtual Analog Controls with Asymptotically Stable Recurrent Neural Networks

Recurrent neural networks are used in virtual analog modeling applications to digitally replicate the sound of analog hardware audio processors. The controls of hardware devices can be used as a conditioning input to these networks. A common method for introducing control conditioning to these models is the direct static concatenation of controls with input audio samples, which we show produces audio artifacts under time-varied conditioning. Here we derive constraints for asymptotically stable variants of commonly used recurrent neural networks and demonstrate that asymptotical stability in recurrent neural networks can eliminate audio artifacts from the model output under zero input and time-varied conditioning. Furthermore, our results suggest a possible general solution to mitigate conditioning-induced artifacts in other audio neural network architectures, such as convolutional and state-space models.