real part of the natural logarithm of the insertion transfer function NOTE - In French, the term 'affaiblissement d'insertion' is also used for a power ratio, defined in IEC 60050-702 and IEC 60050-731, in English 'insertion loss'.the ratio, generally expressed in decibels, of the power delivered to the load impedance before insertion of the filter to the power delivered to the load impedance after insertion of the filter