Seiji Kobayashi

An audio watermarking method using a two-dimensional pseudo-random array

In this paper, we describe a multiple-bit audio watermarking method which is robust against wow-and-flutter, random sample cropping, and pitch shifting. Though these processings are easy to perform, they are difficult for audio watermarks to survive, because they introduce mis-synchronization between the embedded and detection watermarks. Our main ideas against these mis-synchronization attacks are a two-dimensional pseudo-random array (PRA), magnitude modification, and non-linear subbands. The embedding algorithm modifies the magnitudes of segmented areas in the time-frequency plane of the content, according to a two-dimensional pseudo-random array, while the detection algorithm correlates the magnitudes with the PRA. The two-dimensional array makes the watermark robust against cropping because, even when some portions of the content are heavily degraded, other portions of the content can match the PRA and contribute to watermark detection. Secondly, the magnitude modification enables detection even from displaced detection windows. This is because magnitudes are less influenced than phases by fluctuations of the analysis windows caused by random cropping. The last idea, wider bandwidths at higher frequencies, keeps the correspondence of the embedded and detection PRA even for pitch-shifted content. We theoretically and experimentally analyze the robustness of the proposed algorithm against a variety of signal degradations.

Audio watermarking method robust against time- and frequency-fluctuation

In this paper, we describe an audio watermarking algorithm that can embed a multiple-bit message which is robust against wow-and-flutter, cropping, noise-addition, pitch-shift, and audio compressions such as MP3. The algorithm calculates and manipulates the magnitudes of segmented areas in the time-frequency plane of the content using short-term DFTs. The detection algorithm correlates the magnitudes with a pseudo-random array that maps to a two-dimensional area in the time-frequency plane. The two-dimensional array makes the watermark robust because, even when some portions of the content are heavily degraded, other portions of the content can match the pseudo-random array and contribute to watermark detection. Another key idea is manipulation of magnitudes. Because magnitudes are less influenced than phases by fluctuations of the analysis windows caused by random cropping, the watermark resists degradation. When signal transformation causes pitch fluctuations in the content, the frequencies of the pseudo-random array embedded in the content shift, and that causes a decrease in the volume of the watermark signal that still correctly overlaps with the corresponding pseudo-random array. To keep the overlapping area wide enough for successful watermark detection, the widths of the frequency subbands used for the detection segments should increase logarithmically as frequency increases. We theoretically and experimentally analyze the robustness of proposed algorithm against a variety of signal degradations.

Automatic music monitoring and boundary detection for broadcast using audio watermarking

An application of watermarking for automatic music monitoring of radio broadcasts is discussed. By embedding information into the music as a watermark before broadcasting it, it is possible to keep track of what music has been on the air at what time, and for how long. However, to effectively implement this application, the handling of content transitions is important, because the detection reliability deteriorates at the content boundaries. In this paper, a method of detecting content boundaries using overlapping detection windows is described. The most probable pattern of content transition is selected under the condition that detection results from multiple windows are available. The derived rules are represented using a finite state model, which is useful for detection in real time. Experimental results on FM radio broadcasts are also presented.