A method and apparatus are provided for estimating the noise spectrum of an audio signal occupying a certain frequency range. The package 13 is provided with a stepped level-difference 26 in the inner wall surface, and an internal contact electrode 14 formed on the upper surface of the stepped level-difference 26. The instrumentation of the present invention, all of which is inserted from a lateral position into the spine in the preferred embodiment, comprises a guide pin, a distractor, an extended outer sleeve, an inner sleeve an adjustable drill and an implant driver. AlsoIn addition, the generated watermark may comprise one or more of a unique identifier for the device, a source of the data, for example, a service provider, a date and a time.