<p>Increased walking variability is associated with risk of falling in older adults. Walking to a beat (Rhythmic Auditory Stimulation; RAS) can improve walking performance, however not all individuals benefit. Previous research shows that older adults show greater costs to performance compared to younger adults when performing a cognitive and a motor task simultaneously (i.e., dual tasking), particularly when the cognitive task is complex. The current study conceptualizes RAS as a dual-task situation (i.e., walking and synchronizing) with the aim of better understanding response (positive or negative) to RAS. We hypothesized that increasing task complexity would attenuate the benefit of RAS, particularly for older age groups. Young, middle-aged, and older adults performed walking as a single task and in three dual-task conditions: while synchronizing steps to low tones (<i>Simple</i>); to low and high tones (<i>Moderate</i>); to low and high tones while monitoring for a target sequence of tones (<i>Complex</i>). Middle-aged adults improved their walking in the <i>Simple</i> condition relative to walking in silence, but younger and older adults did not. This benefit was attenuated in the <i>Complex</i> condition. Stronger beat perception was associated with greater benefit to walking in the <i>Complex</i> condition. Stronger auditory selective attention was associated with greater benefit to walking in the <i>Moderate</i> condition. In conclusion, task complexity modulated response to RAS in middle-aged adults. Beat perception and selective auditory attention supported a positive response to RAS. Understanding when RAS benefits versus interferes with walking can help individuals optimize their environment to reduce risk of falls.</p>