Possible Methods of Copy-Restriction for Analog Audio Recording

Copy-restricted Recordings

It is possible to add inaudible artifacts to a recording that will, to a limited extent, interact with the subsequent recording (i.e. copying) process to generate audible tones or other artifacts that significantly degrade the quality and value of such copies.

The advantage of such a method is that it requires no modification to the reproducing system, but instead derives its operational effect from the nature of the recording process itself.

The disadvantage of the method is that its effectiveness is based on assumptions about specific operational parameters of the copying system which may not be true and which are not under the control of the copyright holder, reducing or eliminating the effectiveness of the method. Also, such methods may be comparatively easily defeated by a knowledgeable recordist.

Copy-restricted Recordings/Systems
In a copy-restricted system, some inaudible (see above - "Effect on Copyrighted Work") modification or artifact is added to the copy-restricted recording that provides a unique "signature" that can be detected by the circuitry in a subsequent recorder (i.e. copying) system, which in turn disables the recording mechanism whenever such a signature is detected.

The advantages of such a system are that it positively identifies copy-restricted recordings and restricts only those recordings and it completely inhibits copying (instead of simply making a degraded copy). Further, such systems may be used to inhibit "analog realm" digital recorder copies (i.e. digital recordings that are copied via a transfer into the analog realm to defeat digital code copy-restriction protocols - in fact the CBS Copycode system for Digital Audio Tape recorders was proposed for use in exactly this way).

The disadvantages are that the effectiveness is limited by the extent to which recorders in use are fitted with detecting/disabling circuits, and the quite substantial cost of adding such hardware modifications to all recorders (which may prove to be a substantial part of the cost of each such recorder, if principles of reliability and performance are to be met).

Comment
It is my opinion that the cost, difficulty in implementation and unreliability of the above technologies make their generalized adoption undesirable and/or ineffective, particularly given the rapid transition being made from analog to digital recording. By the time that analog recording systems may be broadly equipped with copy-restriction detecting/disabling circuits, such recording systems will generally have fallen into obsolescence and disuse.

There is a further political issue: a significant segment of the general "recording" public objects to the modification of any analog recording, believing that such modifications are generically "audible." Again, the CBS Copycode case is instructive: the primary objection to the system by the "recording" public was that it would audibly degrade recordings. When this was confirmed by the National Bureau of Standards, it was generally reported as being the primary reason for the system to be regarded as not fulfilling its design objective, while scant attention was paid to the fact that the primary problem with the system was reliability (i.e. the proposed system simply did not work – it often failed to inhibit the copying of encoded recordings and often inhibited the recording of unencoded recordings).