Amplifiers are classified under heading 8518 and sub-heading 8543.70. Amplifiers of sub-heading 8518.40 are used to amplify electrical signals which are within the frequency range audible by human beings. Such amplifiers reside in sub-heading 8518.50 when they are as a set. Those of sub-heading 8543.70 are used to amplify mid and high frequency range audio signals. Moreover, amplifiers that are used to perform functions other than audio amplifying, such as sound mixing or combining, are also classified under sub-heading 8543.70. Amplifiers used for data communication and telecommunication processing, are classified under sub-heading 8517.62. Integrated circuits comprising amplifiers reside in sub-heading 8542.33.