Science News: To determine the dimensions of a room without use of a tape measure, researchers have used a speaker, five microphones, and a mathematical algorithm. As they explain in their paper published in the Proceedings of the National Academy of Sciences, Ivan Dokmanić of the Swiss Federal Institute of Technology in Lausanne and coworkers were able to sift through the multiple echoes bouncing off the walls and ceiling of a convex polyhedral room, group the echoes by which surface they bounced off of, and use that data to accurately describe the interior. Such a technique could be used to improve teleconferencing and online video gaming by minimizing echoes. The group is now working to refine the technique so that rooms could be mapped with a cellphone.
BBC: Only one in 10 000 people have perfect pitch—the ability to identify a given musical note without the help of a reference note. Although long believed to be innate, perfect pitch may not be so perfect after all, say Howard Nusbaum of the University of Chicago and his colleagues. In their paper published in Psychological Science, the researchers discuss their study in which they played a long piece of music to a group of 27 people with perfect pitch. Over a period of 45 minutes, the researchers gradually turned the tones slightly flat. Not only did the change go unnoticed, but when the tones were returned to normal, the listeners claimed they sounded too sharp. The researchers determined that the ability to recognize pitch, rather than being absolute, can change with listening experience. Next they hope to see whether adults without perfect pitch can improve in their ability to recognize notes.
Science: Scientists have long puzzled over how such a small animal as a cicada can produce such a deafening drone. Now Derke Hughes of the US Naval Undersea Warfare Center and colleagues have used microcomputed tomography to image the tiny noise-making structures, called tymbals, that are on either side of a cicada’s abdomen. Each of a cicada’s two tymbals consists of a series of microscopic ribs connected by a membrane. Unlike many insects, which make noise by rubbing body parts together, cicadas cause the tymbals to vibrate. They pull the tymbals’ ribs together and then allow them to snap apart some 300–400 times per second, and the sound is amplified by the creatures’ hollow abdomen. Some cicadas can produce sounds up to 120 decibels—loud enough to cause hearing loss in humans. The investigators hope to use their study of cicadas to improve current sonar systems for underwater exploration.
Daily Mail: Amanda Ghassaei, a software engineer from California, has previously shown how to use 3D printers to make vinyl music records. Now she has posted online instructions for an alternative method that uses a laser cutter to cut records out of wood. The process involves converting an MP3 into a digital waveform, which is then saved as a pdf. The pdf becomes the “vector cutting path” that the laser cutter follows to carve the pattern into the wood. Because the laser’s resolution is relatively low, the groove is twice as thick as a normal record groove. Hence, only about three minutes of music will fit on a standard-sized record, and the sound fades to static the closer the needle moves to the center as the sampling rate decreases. If no laser cutter is available, Ghassaei says that a computer numerically controlled (CNC) mill or CNC razor-blade paper cutter could also be used. Because of the lower resolution, the technique works best with songs that are dominated by low- to mid-range sounds. Ghassaei provided a video of one of the records playing Radiohead’s “Idioteque.”
BBC: The greater wax moth has been shown in a recent study to be able to detect some sounds with frequencies up to 300 kHz. In comparison, humans top out at 20 kHz and dolphins, which can communicate in ultrasound, at 160 kHz. The study was led by James Windmill of Strathclyde University in Glasgow, Scotland, who says the moths may have evolved the capability as a defensive response to predatory bats, which employ ultrasound to communicate. Ultrasound waves degrade quickly when traveling through air, so a better understanding of how moths utilize the frequencies might help Windmill ‘s team and other scientists in the development of microacoustic devices such as miniature microphones.
Smithsonian: A wealth of early sound recordings made by Alexander Graham Bell and his assistants in the late 19th century have long remained “mute artifacts” because the method of playing them back was unknown. Now more than a century later, Bell’s voice has been heard for the first time. Researchers at the Smithsonian’s National Museum of American History, which holds a cache of more than 400 of Bell’s wax-and-cardboard disks and cylinders, teamed up with researchers at the Library of Congress and Lawrence Berkeley National Laboratory (LBNL). To create digital audio files of Bell’s recordings, LBNL researchers used the optical measurement technique they had developed to align the silicon detectors in the ATLAS experiment at CERN. They took multiple high-resolution images of the soundtracks, moving the camera in a spiral pattern to follow the path of the grooves, then used a computer to calculate the sound pressure waveform and used the data to create the audio file. The result was the sound of muffled voices reciting Hamlet’s soliloquy, number sequences, and “Mary Had a Little Lamb.” By deciphering notes scratched in wax on one of the disks, dated 15 April 1885, they discovered a recording of Bell himself. Perhaps reminiscent of Bell’s father, who was a renowned elocution teacher, Bell can now be heard making the ringing declaration, “In witness whereof—hear my voice, Alexander Graham Bell.”
Science News: Most cloaking devices attempt to prevent sound or light waves from reflecting by redirecting the waves around the cloaked object. José Sánchez-Dehesa of the Polytechnic Institute of Valencia in Spain and his colleagues have taken a different approach and created a cloak that uses the same principle as noise-canceling headphones. They created a design of 60 rings of varying sizes that form a cage-like structure around a sphere and used a 3D printer to make the rings. The rings are shaped and placed in such a way that the reflected sound waves interfere with each other, resulting in no detectable reflected sound wave. The researchers tested the cloak by hanging the caged sphere in an anechoic chamber and shooting it with sound waves. For most frequencies, sensors were able to detect reflections, but at 8.55 kHz, they detected nothing. While a very small step forward in sound cloaking, this is the first time that an object has been hidden in three dimensions. Future applications could range from reducing public noise pollution to creating stealthier submarines.
Ars Technica: Humans hear by using their ears to detect vibrations and their brain to translate those vibrations into nerve inpulses. Most models of human hearing assume that the sound measurements made by the ear and brain are linear. The result is a direct correlation between the abilities to accurately determine the frequency and the duration of a sound. Such linear models are used in modern audio compression algorithms to save space by removing presumably inaudible tones. To fine-tune the model, Jacob Oppenheim and Marcelo Magnasco of Rockefeller University in New York tested the ability of subjects to determine both the frequency and duration of so-called Fourier-limited sound pulses. Such pulses are pairings of specific frequencies and shortest possible durations that together result in the minimum amount of uncertainty possible according to linear models. The researchers found that across the board the test subjects outperformed by a factor of 10 the linear model’s predictions for ability to determine the sound pulses’ frequency, duration, or both. Better understanding of the way that humans detect sound may produce audio compression algorithms that improve sound quality and don’t cut out parts of the sound that people can actually hear.
Ars Technica: In 2001, seismometers in the Spokane, Washington, area recorded more than 100 earthquakes, some as large as magnitude 4.0. One of the characteristics of the 2001 activity was the reports of loud booms, which are often associated with small quakes. Examining data recorded by the European Space Agency’s GOCE satellite during the 2011 Tohoku earthquake, an international team of researchers has determined that large earthquakes also produce sound waves, but at infrasonic wavelengths. The satellite’s accelerometer detected the passing sound wave at an altitude of 270 km. It was also able to detect changes in atmospheric density due to the sound wave’s compression of the air. The compression increased the drag on the satellite, causing it to activate control jets to maintain a precise orbit. Researchers from the US Geological Survey and the Pacific Northwest Seismic Network have begun using satellite data to understand the nature of seismic events in the area. Interferometric synthetic aperture radar measurements from European Space Agency and Canadian Space Agency satellites showed surface movement of 15 mm along a thrust fault that passes through the city’s center. Computer models suggest that the quake activity was centered at depths of 0.3 to 2 km.
Science: Dolphins, which are known for their complex cognitive and social behavior, appear to be able to call each other—by whistling. Stephanie King of the University of Saint Andrews in the UK and her colleagues studied recordings made by the Sarasota Dolphin Research Program of 250 wild bottlenose dolphins that were briefly captured between 1984 and 2009; they also looked at 4 captive dolphins. All dolphins have their own distinctive whistle, learned from their mothers. But the dolphins in the study also could imitate the whistle of their closest social partner—such as mothers and their calves, or allied males. “They produce the copies when they are separated, which we think shows that they want to reunite with a particular individual,” said King. Now her group hopes to expand its study beyond captured dolphins to see how dolphins use their whistling ability in the wild.