Encoding and decoding of information in audio signals

Abstract

Systems and methods are provided for decoding a message symbol in an audio signal. This message symbol is represented by first and second code symbols displaced in time. Values representing the code signals are accumulated and the accumulated values are examined to detect the message symbol.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS AND U.S. PATENT DOCUMENT[0001]This is an application to reissue U.S. Pat. No. 6,871,180 issued Mar. 22, 2005 from application Ser. No. 09 / 318,045 filed May 25, 1999.BACKGROUND OF THE INVENTION[0002]The present invention relates to methods and apparatus for extracting an information signal from an encoded audio signal.[0003]There are various motivations to permanently or indelibly incorporate information signals into audio signals, referred to as “watermarking.” Such an audio watermark may provide, for example, an indication of authorship, content, lineage, existence of copyright, or the like for the audio signals so marked. Alternatively, other information may be incorporated into audio signals either concerning the signal itself or unrelated to it. The information may be incorporated in an audio signal for various purposes, such as identification or as an address or command, whether or not related to the signal itself.[0004]There is considera...

AI Technical Summary

Benefits of technology

[0009]Therefore, an object of the present invention is to provide systems and methods for detecting code symbols in audio signals which alleviate the problems caused by periods of low signal levels and burst errors.

[0010]It is another object of the invention to provide such systems and methods which afford reliable operation under adverse conditions.

[0011]It is a further object of the invention to provide such systems and methods which are robust.

Problems solved by technology

During a lengthy period of low amplitude levels, it may be difficult to incorporate a code signal in an audio signal without causing the encoded audio signal to differ from the original in an acoustically perceptible manner.

A further problem is the occurrence of burst errors during the transmission or reproduction of encoded audio signals.

Burst errors may appear as temporally contiguous segments of signal error.

Such errors generally are unpredictable and substantially affect the content of an encoded audio signal.

Burst errors typically arise from failure in a transmission channel or reproduction device due to severe external interferences, such as an overlapping of signals from different transmission channels, an occurrence of system power spikes, an interruption in normal operations, an introduction of noise contamination (intentionally or otherwise), and the like.

In a transmission system, such circumstances may cause a portion of the transmitted encoded audio signals to be entirely unreceivable or significantly altered.

Absent retransmission of the encoded audio signal, the affected portion of the encoded audio may be wholly unrecoverable, while in other instances alterations to the encoded audio signal may render the embedded information signal undetectable.

In many applications, such as radio and television broadcasting, real-time retransmission of encoded audio signals is simply unfeasible.

In systems for acoustically reproducing audio signals recorded on media, a variety of factors may cause burst errors in the reproduced acoustic signal.

Commonly, an irregularity in the recording media, caused by damage, obstruction, or wear, results in certain portions of recorded audio signals being unreproducable or significantly altered upon reproduction.

Also, misalignment of or interference with the recording or reproducing mechanism relative to the recording medium can cause burst-type errors during an acoustic reproduction of recorded audio signals.

Further, the acoustic limitations of a speaker as well as the acoustic characteristics of the listening environment may result in spatial irregularities in the distribution of acoustic energy.

Such irregularities may cause burst errors to occur in received acoustic signals, interfering with code recovery.

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