First of all lets agree on the point that auditor is required to obtain sufficient appropriate audit evidence to form reasonable conclusions and on the same conclusions auditor base his opinion. If we are clear on this part than we are half way through.
The next question is how auditor is going to obtain sufficient appropriate audit evidence? This question is answered in the form of selecting appropriate audit methodology or in other words audit approach. Selecting the right audit approach is important in many aspects and is selected by the auditor by considering many factors including nature of audit engagement and the circumstances surrounding the engagement, cost-benefit analysis, time, resources and skills available etc. There are different approaches to conduct the audit which are as follows:
- Substantive approach
- Systems-based approach
- Transaction cycle approach
- Directional testing
- Risk-based approach
Whereas the procedures are the tasks that are carried out after a particular methodology is selected. Procedures are applied or executed in the form of confirmation, recalculation, re-performance, inquiry, observation etc.
Simply put, procedures are defined on the basis of the methodology adopted by the auditor. Approach/methodology will determine what needs to be found, done or executed whereas, procedures are the tasks that will find, do or execute what was determined in accordance with the approach.
As per your question, in substantive approach auditor right from the beginning will go detailed testing which will surely involve substantive procedures. However, substantive procedures can be applied even if substantive approach is not selected. For example if auditor is following risk based approach and he establishes that internal control system is working efficiently and effectively then he will apply procedures to test the system i.e. test of controls and just to confirm that his preliminary risk assessment was correct he will apply substantive procedures alongside tests of controls.