Initially, voice signal components are extracted from the audio signal in a procedure for determining a measure of quality of an audio signal. The adaptor-side circuit converts a high alternating voltage coming from a power source to a low direct voltage and has a positive output terminal and a negative output terminal. There is a gusset on the bottom edge and on the side edges from the bottom to the fold lines. The trench in this regard comprises a sidewall air-gap immediately adjacent the side walls of the trench and the conductive metal column, the sidewall air-gap extending down to the via to a depth below a line fixed by the bottom of the trench, and continues downward in the via for a distance of from about 1 Angstrom below the line to the full depth of the via. By preparing solid preparations for oral use composed of a trace amount of the drug ingredient together with pharmaceutical carriers, it is possible to provide tablets which contain the drug component in a uniform content and can be easily and quantitatively taken. A part of the base plate holding an area of the electronic circuit board generating a large quantity of heat is composed of the metal.