Internal soundgen function.
checkInputType(x)
path to a .wav or .mp3 file, Wave object, or a numeric vector representing the waveform with specified samplingRate
Checks the types of audio input to another function, which could be a folder with audio files, a single file, a Wave object, or a numeric vector. The purposes of this helper function are to ascertain that there are some valid inputs and to make a list of valid audio files, if any.