Any frequency other than zero Hz is AC, in that the direction of the current alternates at some rate. Digital signals and analog audio signals both contain a mix of many non-zero frequency components that are simultaneously present. Certain digital signals may have a significant DC component in addition to their AC frequency components, an example being USB signals which have one of their two voltage states at or near zero, and the other at some positive voltage. But a signal having both DC and AC components is nevertheless "operating in an AC circuit," it seems to me.
So the only audio-related cables I can think of which are "not operating in an AC circuit" are cables conducting the outputs of DC power supplies that are external to the component being powered.
Regards,
-- Al