1. A computer-implemented method performed by a speech recognition system having at least a processor, the method comprising: obtaining, by the processor, a frequency spectrum of an audio signal data; extracting, by the processor, periodic indications from the frequency spectrum; inputting, by the processor, the periodic indications and components of the frequency spectrum into a neural network; estimating, by the processor, sound identification information from the neural network; and performing, by the processor, a speech recognition operation on the audio signal data to decode the audio signal data into a textual representation based on the estimated sound identification information, wherein the neural network includes a plurality of fully-connected network layers having a first layer that includes a plurality of first nodes and a plurality of second nodes, and wherein the method further comprises training the neural network by initially isolating the periodic indications from the components of the frequency spectrum in the first layer by setting weights between the first nodes and a plurality of input nodes corresponding to the periodic indications to 0.