A hearing prosthesis system (101, 200) comprising: a first receiver (102, 232) arranged to receive an input signal (110,210), the input signal (110, 210) having at least one audio attribute; output circuitry (105, 238) for providing an output to a user; and a processor (104, 230) arranged to transform the input signal (110, 210) into a transformed signal and to provide the transformed signal to the output circuitry (105, 238), wherein the output circuitry (105, 238) provides the output based on the transformed signal, wherein transforming the input signal into the transformed signal comprises (i) applying a candidate signal processing function to the input signal to generate a candidate transformed signal having a first modification of the audio attribute, (ii) applying a reference signal processing function to the input signal to generate a reference transformed signal having a second modification of the audio attribute, the second modification being different than the first modification, (iii) determining which of the candidate transformed signal and reference transformed signal has better quality, and (iv) outputting as the transformed signal the determined signal, wherein the processor (104, 230) repeatedly conducts the transforming, the hearing prosthesis system (101, 200) further comprising: in one instance of conducting the transforming, the candidate signal processing function has one or more candidate signal processing parameters and the reference signal processing function has one or more reference signal processing parameters different than the one or more candidate signal processing parameters, and wherein if in the one instance of conducting the transforming, the processor (104, 230) determines that the reference transformed signal has better quality than the candidate transformed signal, the processor (104, 230) then changes the candidate signal processing function characterized in that the processor (104, 230) changes the candidate signal processing function to have as the one or more candidate signal processing parameters the one or more reference signal processing parameters, so as to have a modified candidate signal processing function for a next instance of conducting the transforming. a first receiver (102, 232) arranged to receive an input signal (110,210), the input signal (110, 210) having at least one audio attribute; output circuitry (105, 238) for providing an output to a user; and a processor (104, 230) arranged to transform the input signal (110, 210) into a transformed signal and to provide the transformed signal to the output circuitry (105, 238), wherein the output circuitry (105, 238) provides the output based on the transformed signal, wherein transforming the input signal into the transformed signal comprises (i) applying a candidate signal processing function to the input signal to generate a candidate transformed signal having a first modification of the audio attribute, (ii) applying a reference signal processing function to the input signal to generate a reference transformed signal having a second modification of the audio attribute, the second modification being different than the first modification, (iii) determining which of the candidate transformed signal and reference transformed signal has better quality, and (iv) outputting as the transformed signal the determined signal, wherein the processor (104, 230) repeatedly conducts the transforming, the hearing prosthesis system (101, 200) further comprising: in one instance of conducting the transforming, the candidate signal processing function has one or more candidate signal processing parameters and the reference signal processing function has one or more reference signal processing parameters different than the one or more candidate signal processing parameters, and wherein if in the one instance of conducting the transforming, the processor (104, 230) determines that the reference transformed signal has better quality than the candidate transformed signal, the processor (104, 230) then changes the candidate signal processing function in one instance of conducting the transforming, the candidate signal processing function has one or more candidate signal processing parameters and the reference signal processing function has one or more reference signal processing parameters different than the one or more candidate signal processing parameters, and wherein if in the one instance of conducting the transforming, the processor (104, 230) determines that the reference transformed signal has better quality than the candidate transformed signal, the processor (104, 230) then changes the candidate signal processing function characterized in that the processor (104, 230) changes the candidate signal processing function to have as the one or more candidate signal processing parameters the one or more reference signal processing parameters, so as to have a modified candidate signal processing function for a next instance of conducting the transforming.