Abstract: Methods, apparatus, systems and articles of manufacture (e.g., physical storage media) to detect media watermarks in magnetic field data are disclosed herein. Example methods disclosed herein to detect media watermarks can include accessing multidimensional magnetic field data representative of values of a magnetic field measured within a first distance of audio circuitry that is to output an audio signal corresponding to media presented by a media device. Such example methods can also include processing the multidimensional magnetic field data to detect a watermark included in the audio signal.

Abstract: Methods and apparatus are disclosed for updating an index of a reference data database. An example method includes, in response to receiving reference data at a reference database, inserting the reference data in a first portion of the reference database, updating a first portion of an index corresponding to the first portion of the reference database; and updating a second portion of the reference database by shifting the reference data from the first portion of the reference database to the second portion of the reference database, and after shifting, recomputing a second portion of an index corresponding to the second portion of the reference database.

Abstract: Methods and apparatus to present supplemental media on a second screen are disclosed. An example method includes obtaining, at a digital media device, media identifying data from audio data of a portion of first media being presented via the digital media device; determining that the portion of the first media is an advertisement based on the media identifying data; detecting, at the digital media device, a command to cause the digital media device to skip the portion of the first media; and providing an indication to a second device in response to detecting the command, the indication to cause the second device to present second media.

Abstract: Example methods, apparatus, systems and articles of manufacture to implement down-mixing compensation for audio watermarking are disclosed. Example methods disclosed herein to compensate for audio channel down-mixing when embedding watermarks in a multichannel audio signal include obtaining a watermark to be embedded in respective ones of a plurality of audio channels of the multichannel audio signal. Such example methods also include embedding the watermark in a first one of the plurality of audio channels based on a compensation factor that is to reduce perceptibility of the watermark when the first one of the plurality of audio channels is down-mixed with a second one of the plurality of audio channels after the watermark has been applied to the first and second ones of the plurality of audio channels.

Abstract: Methods and apparatus for multi-purpose metering are disclosed. An example method includes transmitting a first discovery inquiry message in response to a wakeup timer expiration signal, disabling a media detection circuit of the portable device when a base unit responds to the discovery inquiry message, and enabling the media detection circuit of the portable device when the base unit response to the discovery inquiry message is absent.

Abstract: Methods and apparatus for multi-purpose metering are disclosed. An example method includes acquiring a rate of data transfer to/from the monitored location and comparing the acquired rate of data transfer to a threshold. The example method also includes setting at least one media monitoring device in a first bandwidth mode when the acquired rate of data transfer exceeds the threshold, and setting the at least one media monitoring device in a second bandwidth mode when the acquired rate of data transfer is below the threshold.

Abstract: Methods and apparatus to perform audio watermark detection and extraction are disclosed. An example method includes sampling a media signal to generate samples, wherein the media signal includes an embedded message, determining a first symbol value for a first block of the samples, determining a second symbol value for a second block of the samples, and determining, using a processor, a resulting symbol value, representative of a part of the embedded message, based on the first symbol value and the second symbol value for the first block of samples and the second block of samples, wherein the first block and the second block partially overlap.

Abstract: Methods and apparatus are disclosed for identifying media and, more particularly, to methods and apparatus for decoding identifiers after broadcast. An example method includes a portion of an identifying code from a media signal, determine a partition of the look-up table based on the portion of the identifying code wherein the partition of the look-up table includes reference signatures associated with the portion of the identifying code, and identify the media signal by comparing a signature extracted from the media signal to reference signatures in the partition of the look-up table.

Abstract: Methods and apparatus for performing variable block length watermarking of media are disclosed. An example method to encode auxiliary data in audio data comprises selecting a frequency based on a code, selecting a block size based on the code, a combination of the block size and the frequency to represent of the code, encoding the code in an audio stream according to the block size and the frequency, and transmitting the audio stream including the encoded code.

Abstract: Methods and apparatus to predict audience composition and solicit audience members are disclosed. A method to predict audience composition for future media involves obtaining indications of intent from first audience members to consume first media, determining a portion of the first audience members that were actually exposed to the first media, and predicting audience composition for a second media of second audience members based on the portion of the first audience members.

Abstract: Methods and apparatus for characterizing media are described. An example method includes converting at least a portion of a block of audio into a frequency domain representation, dividing the frequency domain representation into bands, determining a characteristic difference of a first band of the bands, and determining a signature bit based on the characteristic difference, wherein determining the signature bit is performed differently based on whether an index of the first band has a first property.

Abstract: Methods and apparatus to tracker web browsing sessions are disclosed. An example method includes computing a sequence of numbers to be generated by a random number generator during a first browsing session associated with a browser given a first seed value; and determining whether a web site visit is associated with the first browsing session based on a received number.

Abstract: Methods and apparatus for multi-purpose metering are disclosed. An example method includes acquiring a rate of data transfer to/from the monitored location and comparing the acquired rate of data transfer to a threshold. The example method also includes setting at least one media monitoring device in a first bandwidth mode when the acquired rate of data transfer exceeds the threshold, and setting the at least one media monitoring device in a second bandwidth mode when the acquired rate of data transfer is below the threshold.

Abstract: Methods, apparatus, and articles of manufacture are disclosed in which auxiliary information is added to or removed from an audio signal. In one example, the information may be added to the audio signal using at least two frequencies that are dictated by two different frequency transformation block sizes, such that the two frequencies are not fully visible when an incorrect block size is used to perform a frequency transformation. Additionally, in another example, a decoder may compensate for time and frequency affects caused by removing old samples and adding new samples, which, in one example, alleviates the need to perform repeated frequency transformation using different frequency transformation block sizes. Other examples are described.

Abstract: Methods and apparatus for characterizing media are described. In one example, a method of characterizing media includes capturing a block of audio; converting at least a portion of the block of audio into a frequency domain representation; dividing the frequency domain representation into a plurality of bands; determining a characteristic difference of a first band of the plurality of bands based on a comparison of a characteristic of the first band and a characteristic of a second band different from the first band, wherein the characteristic of the first band occurs at a time that is different than a time at which the characteristic of the second band takes place; and determining a signature bit based on a characteristic difference. Other examples are shown and described.

Abstract: Methods and apparatus for characterizing media are described. A disclosed example apparatus includes a transformer, a decision metric processor, a signature determiner, and a processor to implement the transformer, the decision metric processor, and/or the signature determiner. The example transformer is to convert at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components. The example decision metric processor is to: define a band of the frequency components; determine a difference in energy between a first convolution of a first complex vector with a first group of frequency bins in the band and a second convolution of a second complex vector with a second group of frequency bins in the band; and determine a decision metric for the band based on the difference. The example signature determiner is to determine a signature based on a value of the decision metric.

Abstract: Methods and apparatus to audio watermarking and watermark detection and extracted are described herein. An example method includes receiving a media content signal, sampling the media content signal to generate samples, storing the samples in a buffer, determining a first sequence of samples in the buffer, determining a second sequence of samples in the buffer, wherein the second sequence of samples is of substantially equal length as the first sequence of samples, calculating an average of the first sequence of samples and the second sequence of samples to generate an average sequence of samples, extracting an identifier from the average sequence of samples, and storing the identifier in a tangible memory.

Abstract: Methods and apparatus for characterizing media are described. An example apparatus includes a transformer to convert at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components; a decision metric processor to: define a band of frequency components having real and imaginary spectral components, define a plurality of frequency bins within the band, determine respective difference functions for each of the frequency bins using a product of the real and imaginary spectral components of a corresponding group of the frequency bins, the corresponding group for a first one of the frequency bins including at least the first one of the frequency bins and a second one of the frequency bins selected based on the first frequency bin, and determine a decision metric by summing the difference functions; and a signature determiner to determine a signature based on the decision metric.

Abstract: Methods and apparatus to audio watermarking and watermark detection and extracted are described herein. An example method includes receiving a media content signal, sampling the media content signal to generate samples, storing the samples in a buffer, determining a first sequence of samples in the buffer, determining a second sequence of samples in the buffer, wherein the second sequence of samples is of substantially equal length as the first sequence of samples, calculating an average of the first sequence of samples and the second sequence of samples to generate an average sequence of samples, extracting an identifier from the average sequence of samples, and storing the identifier in a tangible memory.

Abstract: Methods and apparatus for characterizing media are described. A disclosed example apparatus includes a transformer, a decision metric processor, a signature determiner, and a processor to implement the transformer, the decision metric processor, and/or the signature determiner. The example transformer is to convert at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components. The example decision metric processor is to: define a band of the frequency components; determine a difference in energy between a first convolution of a first complex vector with a first group of frequency bins in the band and a second convolution of a second complex vector with a second group of frequency bins in the band; and determine a decision metric for the band based on the difference. The example signature determiner is to determine a signature based on a value of the decision metric.