An audio system includes a channel (10) for processing signals. The channel (10) includes a processing module (50) that follows a chain of modules (40) wherein the chain (40) includes a preceding processing module (45). The following processing module (50) is coupled to the preceding processing module (45) in the chain of modules (40) for receiving the output signal (25). The channel (10) further includes a combiner (60). The combiner (60) has two inputs, a first input (65) receives the signal (30) to be processed in the channel (10), and a second input (70) receives a reference signal (75). The combiner (60) further includes an output (80) coupled to an input of the preceding processing module (45) in the chain (40). By coupling a combination of the signal (30) to be processed and the reference signal (75) to the input (55) of the preceding processing module (45) in the chain (40) and by having a correction signal (90) from the processing unit (85) generated in response to a modification of the reference signal (75) in the output signal (25) of the preceding processing module (45) in the chain (40), the amount and type of processing in the preceding processing module (45) in the chain (40) can be estimated in the processing unit (85) and be corrected for in the following processing module (50).