Which research method is better for investigating the impact of music on my client’s mood, qualitative or quantitative?
Good day, I think it is best to use the Mixed method, Sequential-Explanatory design. You need to assess the level of perceived impact then analyze the result, then you will conduct interviews to explore detailed data that can explain the result. You can study more on some papers. https://journals.sagepub.com/doi/abs/10.1177/1525822X05282260?journalCode=fmxd
A major potential limitation of a quantitative study (including the use of a quantitative study as the primary method in a sequential explanatory model) is the need for a large enough N to produce significant results. You can use the G*power program online to determine how large a sample you would need to have enough power to detect an effect.
In addition, you would need a clear set of measures for both your independent and dependent variables. For example, you would need to be able to measure "impact on mood."