# US 7,466,742 B1 · Detection of entropy in connection with audio signals

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- Number: US 7,466,742 B1
- Document ID: US7466742B1
- Status: Granted
- Kind: B1
- Application number: 09/553,776
- Filed: 2000-04-21
- Granted: 2008-12-16
- Earliest claimed: 2000-04-21
- Assignees: Nielsen Media Research, Inc.
- Inventors: Venugopal Srinivasan
- Web page: https://patentgrep.com/patent/US7466742B1

## CPC

- G10L 19/018: Audio watermarking, i.e. embedding inaudible data in the audio signal
- G10L 19/035: Scalar quantisation
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

An encoder calculates an entropy of at least a portion of a signal and encodes the signal with the calculated entropy. A decoder decodes the signal in order to recover the encoded entropy. The decoder may also determine an entropy of the signal and may compare the entropy that it determines to the decoded entropy. The decoder detects compression/decompression based upon results from the comparison, and/or the decoder prevents use of a device based upon results from the comparison.

## Claims

### Claim 1

A decoder having an input and an output, wherein the input receives a signal, which includes an encoded entropy value, wherein the decoder decodes the signal to read the encoded entropy value from the signal, and wherein the output carries a signal based upon the encoded entropy value, and wherein the decoder is configured to calculate an entropy of the signal and compare the calculated entropy to the encoded entropy value.

### Claim 2 (depends on 1)

The decoder of claim 1 wherein the decoder is configured to detect at least one of a compression operation or a decompression operation based on the comparison.

### Claim 3 (depends on 1)

The decoder of claim 1 wherein the decoder is configured to prevent use of a device based on the comparison.

### Claim 4 (depends on 1)

The decoder of claim 1 wherein the decoder is configured to calculate the entropy of the signal based on a sum of probabilities.

### Claim 5

A method of decoding a signal, which includes a first calculated entropy value, the method comprising:
decoding the signal to extract an ancillary code representing the first calculated entropy value from the signal;
calculating a second entropy of the signal;
comparing the second calculated entropy of the signal to the first calculated entropy value; and
providing an output based on the comparison of the second calculated entropy of the signal to the first calculated entropy value.

### Claim 6 (depends on 5)

The method of claim 5 wherein the signal is an audio signal.

### Claim 7 (depends on 5)

The method of claim 5 wherein the first calculated entropy value is based on a sum of probabilities.

### Claim 8 (depends on 5)

The method of claim 5 wherein decoding the signal comprises decoding the signal by amplitude demodulating pairs of frequencies.

### Claim 9 (depends on 5)

The method of claim 5 wherein decoding the signal comprises determining swapping events that correspond to swapping of a spectral amplitude of at least two frequencies in the signal.

### Claim 10 (depends on 5)

The method of claim 5 wherein decoding the signal comprises using frequency hopping.

### Claim 11 (depends on 5)

The method of claim 5 wherein decoding the signal comprises using spectral demodulation.

### Claim 12 (depends on 5)

The method of claim 5 wherein the output prevents playing of the signal.

### Claim 13 (depends on 5)

The method of claim 5 wherein the entropy of the signal is based on a sum of probabilities.