Multiple channels simultaneously provide multiple, modified digital audio signals, respectively, based on the same digital audio input signal. Each channel has a respective nonlinear effects section to apply a nonlinear transfer function, such as one that emulates a vacuum tube guitar amplifier, based on the input signal. In addition, a respective audio effects section is provided in each channel to apply an audio effect, such as a linear audio effect, based on the input signal. This audio effect is set in each channel by a controller. In another embodiment, multi-tracker (e. g. , double tracker) functionality is provided by the multiple channels wherein at least one of the delay effect, pitch shift, and gain change in a channel is automatically changed as a function of the input signal.