There are many reasons to encode an inaudible message in audio data and many groups would like to have access to such technology. A group with such an interest is the group of copyright owners. Copyright owners would like such an encoding technique to facilitate copyright enforcement and protection. Copyright enforcement would be facilitated by encoding pieces of copyrighted works with a watermark to provide ownership information for copyright enforcement. Alternatively, the copyrights of a work may be protected by a copy protection scheme, e.g. encryption keys encoded onto the audio data, which would prevent unauthorized use of the protected matter.
Another group with an interest in using inaudible messages encoded into audio data would be the group of audio listeners. The encoding would provide listeners with useful information about the programs they are listening to without affecting the audio experience. For example, the names of the performers, the name of the performance, or the name of the broadcaster may be given and relayed to the listener via the listener's receiver.
Still another group with an interest in the encoding of inaudible messages into audio data would be market researchers who make use of audience estimating techniques, as well as customer loyalty programs, commercial verification functionality and program identification. Inaudible messages encoded into broadcast or recorded audio are particularly useful in implementing such techniques and activities.
Yet still another group with an interest in the encoding of inaudible messages into audio data would be those seeking additional bandwidth to communicate data that is totally unrelated to the audio data. For example, telecommunications companies could utilize the bandwidth to carry their data and/or news organizations could relay real time news such as breaking headlines or stock quotes.
There are many other good reasons that other interested groups have for the encoding of inaudible messages into audio data. One problem encounterd in attempting to encode multiple messages inaudibly within audio data is that there is only a limited amount of bandwidth available for this purpose.
The limited bandwidth is due to the fact that audio data can only receive a finite amount of energy in the encoding process before the encoding becomes audible. This level of acceptable ancillary data energy in audio data is application dependent. For example, in high fidelity applications such as music distribution or broadcasting, the messages must be keep inaudible. However, in certain other applications such as voice data communication, e.g. cell phone communications, the constraints on the amount of acceptable ancillary data energy in the audio data are less rigorous. The bandwidth limitations due to these constraints are further restricted by the administrative load imposed by error detection and correction data, marker data, sync data, address data and the like.
A further problem arises in applications requiring the encoding of one or more messages in audio data that is already encoded with another message. This is desired in certain broadcast and recording applications, such as audience measurement, commercial and network clearance, and content identification. It has been proposed to reserve different respective time intervals along the time base of the audio data for encoding of plural messages at various levels of distribution (for example, at the production level, the network level and the local affiliate level). Such time division multiplexing of encoded messages substantially restricts bandwidth available for each of the messages and requires a reliable means of determining in each case the permissible time interval for inserting each different message.
Accordingly, what is needed is a way to encode multiple messages inaudibly in audio data in which one or more such messages are encoded in the audio data at different times and/or levels of distribution which achieves desirably high bandwidth and is easily implemented.
It is also desired to provide expanded data communication capability in the limited bandwidth available for ancillary data in an audio channel. It is desired, therefore, to increase the bandwidth afforded by an audio channel to communicate information in the form of ancillary data encoded in the audio data, so that the encoded ancillary data remains inaudible or beneath an acceptable level of audibility when the audio data is reproduced acoustically.