Remote control signaling using audio watermarks

• US 20040169581A1
• Filed: 03/05/2004
• Published: 09/02/2004
• Est. Priority Date: 02/16/2000
• Status: Abandoned Application

• Current Assignee: Verance Corporation
• Original Assignee: Verance Corporation
• Inventors: Petrovic, Rade, Winograd, Joseph M.
• Application Number:
  US10/794,520
• Publication Number:
  US 20040169581A1
• Time in Patent Office: Days
• US Class Current: 340/5.2
• CPC Class Codes: G06F 7/00 Methods or arrangements for processing data by operating upon the order or content of the data handled logic circuits H03K19/00
• CPC Class Codes: G06Q 30/0264 based upon schedule
• CPC Class Codes: G08C 23/02 using infrasonic, sonic or ultrasonic waves
• CPC Class Codes: G10L 19/018 Audio watermarking, i.e. embedding inaudible data in the audio signal
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves

Abstract

A system for using a watermark embedded in an audio signal to remotely control a device. Various devices such as toys, computers, and appliances, equipped with an appropriate detector, detect the hidden signals, which can trigger an action, or change a state of the device. The watermarks can be used with a “time gate” device, where detection of the watermark opens a time interval within which a user is allowed to perform an action, such as pressing a button, typing in an answer, turning a key in a lock, etc. To prevent fraudulent activation of a time gate, the time gate device can be configured to react only to watermarks coming from live broadcasts, and not from replays from tapes or other storage devices. In another feature, robustness of the watermark is improved, e.g., for acoustic propagation channels, by shifting the detection time of the watermark based on a measured bit error count of the watermark. Furthermore, the watermark may be inserted before the desired action along with corresponding offset information if the audio signal is not suitable at the time of the action.

Claims

1. A method for robustly embedding data in an audio signal, comprising the step of:

embedding at least a first message as a corresponding first watermark in an audio source signal to provide a composite audio signal by modifying the audio source signal so that data symbols of the first message are determined according to corresponding values of an autocorrelation function of the composite audio signal;

wherein;

the values of the autocorrelation function are determined using delays that differ for adjacent data symbols; and

the first watermark is carried substantially inaudibly in the composite audio signal.

2. The method of claim 1, wherein:

each autocorrelation value is calculated over a time interval of a corresponding data symbol.

3. A method for recovering data that is robustly embedded in an audio signal, comprising the steps of:

(a) receiving a composite audio signal;

wherein;

at an encoder, at least a first message is embedded as a corresponding first watermark in an audio source signal to provide the composite audio signal by modifying the audio source signal so that data symbols of the first message are determined according to corresponding values of an autocorrelation function of the composite audio signal;

the values of the autocorrelation function are determined using delays that differ for adjacent data symbols; and

the first watermark is carried substantially inaudibly in the composite audio signal; and

(b) recovering the first message from the composite audio signal.

4. The method of claim 3, wherein:

each autocorrelation value is calculated over a time interval of a corresponding data symbol.

5. A method for robustly embedding data in an audio signal, comprising the steps of:

determining a first, candidate time segment of an audio source signal for embedding at least a first message as a corresponding first watermark to provide a composite audio signal;

evaluating the audio source signal to determine if the first time segment is suitable for masking the first message; and

if the first time segment is found to be unsuitable;

(a) selecting another, second time segment of the audio source signal that is suitable for masking the first message; and

(b) embedding the first message in the second time segment along with information indicative of a time shift between the first and second time segments.

6. The method of claim 5, wherein:

the second time segment precedes the first time segment.

7. A method for recovering embedded data from a composite audio signal, comprising the steps of:

(a) receiving the composite audio signal;

wherein;

at least a first message is embedded as a corresponding first watermark in a first time segment of the composite audio signal, along with time shift information indicative of a time shift between the first time segment and another, second time segment; and

an audio source signal of the composite audio signal is suitable for masking the first message during the first time segment, but is unsuitable for masking the first message during the second time segment;

(b) recovering the first message and the time shift information from the first time segment of the composite audio signal;

(c) determining when the time shift has elapsed in accordance with the time shift information; and

(d) providing a control signal for controlling a device after the time shift has elapsed in accordance with said determining step.

8. The method of claim 7, wherein:

the second time segment precedes the first time segment.

9. A method for decoding embedded data in an audio signal, comprising the step of:

(a) receiving a composite audio signal;

wherein data symbols of at least a first message are embedded as a corresponding first watermark in an audio source signal to provide the composite audio signal, and the first watermark is carried substantially inaudibly in the composite audio signal;

the audio source signal is modified so that data symbols of the first message are determined according to corresponding values of an autocorrelation function of the composite audio signal; and

each autocorrelation value is calculated over a time interval of a corresponding data symbol; and

(b) recovering the embedded data symbols from the received composite audio signal according to polarities of the composite audio signal.

10. A decoding method for improving the time resolution of the position of a message that is embedded in an audio signal, and encoded according to an error-correcting code, comprising the steps of:

(a) receiving the audio signal;

(b) determining an initial position in the audio signal at which the message is initially detected;

(c) determining a bit error count for the message at each of a plurality of positions, including the initial position and at least one other position that is shifted relative to the initial position;

(d) determining an optimum position at which it is most probable that the message is embedded in the audio signal in accordance with the bit error counts; and

(e) recovering the message at the optimum position.

11. The method of claim 10, wherein:

the optimum position is determined according to the position that yields a bit error count that is a minimum among the plurality of positions.

12. The method of claim 10, wherein:

the optimum position is determined according to a mid-point of the positions that yield bit error counts that are minimums among the plurality of positions.