A method for customizing a voice in a multi-media message created by a sender for a recipient is disclosed. The CD also stores an ISRC that specifies the content of the CD, that is, the music data present on the CD. The upper surface of a street area of the substrate is oxidized so that the oxidized region extends under the sealing layer. This prevents a voltage differential at the input of the operation amplifier, eliminating to a great extent undesired signal fluctuations, which could falsify the measurement result. Methods of marketing such products are also contemplated.