Categories
IEEE Spectrum

Coming Soon: Augmented Reality Glasses for the Masses

A lot can change in seven years. Google Glassa wearable display with a camera and other tools that feed wearers information and allow them to capture photos and videos, began shipping to selected developers in 2013. It was released as a more open beta test in 2014. Then, in early 2015, Google withdrew the product. It has since reemerged, along with a variety of competitors, as a specialized product for use in industry—often for training or displaying diagrams or other information during specific tasks.

As a consumer product though, the technology stalled.

Until now, that is. Facebook last month confirmed that it’s building augmented reality (AR) glasses. Apple is rumored to be getting ready to release its own version of AR glasses next year.

But are AR glasses finally ready for prime time?

I asked Nandan Nayampally, vice president and general manager of ARM’s Immersive Experience Group, to consider whether the technology—and consumers—are ready for AR glasses. Here’s what he had to say.

Categories
ScienceDaily

Solving the mystery of quantum light in thin layers

It is an exotic phenomenon that nobody was able to explain for years: when energy is supplied to a thin layer of the material tungsten diselenide, it begins to glow in a highly unusual fashion. In addition to ordinary light, which other semiconductor materials can emit too, tungsten diselenide also produces a very special type of bright quantum light, which is created only at specific points of the material. It consists of a series of photons that are always emitted one-by-one — never in pairs or in bunches. This anti-bunching effect is perfect for experiments in the field of quantum information and quantum cryptography, where single photons are required. However, for years this emission has remained a mystery.

At the TU Vienna an explanation has now been found: A subtle interaction of single atomic defects in the material and mechanical strain is responsible for this quantum light effect. Computer simulations show how the electrons are driven to specific places in the material, where they are captured by a defect, lose energy and emit a photon. The solution to the quantum light puzzle has now been published in the journal Physical Review Letters.

Only three atoms thick

Tungsten diselenide is a so-called “two-dimensional material” that forms extremely thin layers. Such layers are only three atomic layers thick: there are tungsten atoms in the middle, coupled to selenium atoms below and above. “If energy is supplied to the layer, for example by applying an electrical voltage or by irradiating it with light of a suitable wavelength, it begins to shine,” explains Lukas Linhart from the Institute of Theoretical Physics at the TU Vienna. “This in itself is not unusual, many materials do that. However, when the light emitted by tungsten diselenide was analysed in detail, in addition to ordinary light a special type of light with very unusual properties was detected.”

This special nature quantum light consists of photons of specific wavelengths — and they are always emitted individually. It never happens that two photons of the same wavelength are detected at the same time. “This tells us that these photons cannot be produced randomly in the material, but that there must be certain points in the tungsten diselenide sample that produce many of these photons, one after the other,” explains Prof. Florian Libisch, spokesperson of the Graduate School TU-D at the TU Vienna with a focus on two-dimensional materials.

Explaining this effect requires the detailed understanding of the behaviour of the electrons in the material on a quantum physical level. Electrons in tungsten diselenide can occupy different energy states. If an electron changes from a state of high energy to a state of lower energy, a photon is emitted. However, this jump to a lower energy is not always allowed: The electron has to adhere to certain laws — the conservation of momentum and angular momentum.

Defects and distortions

Due to these conservation laws, an electron in a high energy quantum state must remain there — unless certain imperfections in the material allow the energy states to change. “A tungsten diselenide layer is never perfect. In some places one or more selenium atoms may be missing,” says Lukas Linhart. “This also changes the energy of the electron states in this region.”

Moreover, the material layer is not a perfect plane. Like a blanket that wrinkles when spread over a pillow, tungsten diselenide stretches locally when the material layer is suspended on small support structures. These mechanical stresses also have an effect on the electronic energy states.

“The interaction of material defects and local strains is complicated. However, we have now succeeded in simulating both effects on a computer” says Lukas Linhart. “And it turns out that only the combination of these effects can explain the strange light effects.” At those microscopic regions of the material, where defects and surface strains appear together, the energy levels of the electrons change from a high to a low energy state and emit a photon. The laws of quantum physics do not allow two electrons to be in exactly the same state at the same time, and therefore the electrons must undergo this process one by one. This leads to the photons being emitted one by one as well.

At the same time, the mechanical distortion of the material helps to accumulate a large number of electrons in the vicinity of the defect, so that another electron is readily available to step in after the last one has changed its state and emitted a photon.

This result illustrates that ultrathin 2D materials open up completely new possibilities for materials science.

Story Source:

Materials provided by Vienna University of Technology. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

Controlling superconducting regions within an exotic metal

Superconductivity has fascinated scientists for many years since it offers the potential to revolutionize current technologies. Materials only become superconductors — meaning that electrons can travel in them with no resistance — at very low temperatures. These days, this unique zero resistance superconductivity is commonly found in a number of technologies, such as magnetic resonance imaging (MRI). Future technologies, however, will harness the total synchrony of electronic behavior in superconductors — a property called the phase. There is currently a race to build the world’s first quantum computer, which will use these phases to perform calculations. Conventional superconductors are very robust and hard to influence, and the challenge is to find new materials in which the superconducting state can be easily manipulated in a device.

EPFL’s Laboratory of Quantum Materials (QMAT), headed by Philip Moll, has been working on a specific group of unconventional superconductors known as heavy fermion materials. The QMAT scientists, as part of a broad international collaboration between EPFL, the Max Planck Institute for Chemical Physics of Solids, the Los Alamos National Laboratory and Cornell University, made a surprising discovery about one of these materials, CeIrIn5.

CeIrIn5 is a metal that superconducts at a very low temperature, only 0.4°C above absolute zero (around -273°C). The QMAT scientists, together with Katja C. Nowack from Cornell University, have now shown that this material could be produced with superconducting regions coexisting alongside regions in a normal metallic state. Better still, they produced a model that allows researchers to design complex conducting patterns and, by varying the temperature, to distribute them within the material in a highly controlled way. Their research has just been published in Science.

To achieve this feat, the scientists sliced very thin layers of CeIrIn5 — only around a thousandth of a millimeter thick — that they joined to a sapphire substrate. When cooled, the material contracts significantly whereas the sapphire contracts very little. The resulting interaction puts stress on the material, as if it were being pulled in all directions, thus slightly distorting the atomic bonds in the slice. As the superconductivity in CeIrIn5 is unusually sensitive to the material’s exact atomic configuration, engineering a distortion pattern is all it takes to achieve a complex pattern of superconductivity. This new approach allows researchers to “draw” superconducting circuitry on a single crystal bar, a step that paves the way for new quantum technologies.

This discovery represents a major step forward in controlling superconductivity in heavy fermion materials. But that’s not the end of the story. Following on from this project, a post-doc researcher has just begun exploring possible technological applications.

“We could, for example, change the regions of superconductivity by modifying the material’s distortion using a microactuator,” says Moll. “The ability to isolate and connect superconducting regions on a chip could also create a kind of switch for future quantum technologies, a little like the transistors used in today’s computing.”

Story Source:

Materials provided by Ecole Polytechnique Fédérale de Lausanne. Original written by Laure-Anne Pessina. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
3D Printing Industry

AITTIP releases the KRAKEN: a four-in-one hybrid additive manufacturing system

For the past three years, a European collective has been working on the KRAKEN – a hybrid subtractive and additive manufacturing system. The machine is capable of creating objects up to 20 meters long, using three interchangeable 3D printing technologies and a fourth subtractive tool head. Completed at the end of September 2019, the KRAKEN […]

Go to Source
Author: Beau Jackson

Categories
ScienceDaily

Stabilizing multilayer flows may improve transportation of heavy oils

During the past 20 years, the oil industry has begun a gradual transition away from light oils, which are being consumed progressively, toward heavier oils. But transporting heavy oils cost-effectively is a big challenge because heavy oils are viscous — essentially a thick, sticky and semifluid mess.

Stabilizing the interface of multilayer flows for transportation is no easy task. While several potential solutions have been proposed, no one-size-fits-all approach currently exists that works for all applications.

One way to outmaneuver this problem, as University of British Columbia researchers report in Physics of Fluids, from AIP Publishing, is a viscoplastic lubrication (VPL) technique. It can complement existing methods to stabilize interfaces within multilayer flows.

Viscoplasticity describes the characteristic(s) in which a mass acts as a solid below a critical value of stress but flows like a viscous liquid as stress increases.

The researchers’ work focuses on multilayer flows, specifically lubricated pipeline flow. In lubricated pipeline flow, a thin fluid, such as water, is used to lubricate the pipeline via core-annular flows. But this method suffers from interfacial instabilities, which means the oil and water may mix and make it more difficult to separate downstream.

“In multilayer flows, the interfaces between two fluids are highly unstable because of the differences between fluid properties,” said Ian Frigaard, a professor of mechanical engineering and applied mathematics.

Previous work on yield stress fluids by the researchers suggested a new configuration might prevent instabilities from growing. Their VPL technique places a layer of yield stress fluid between the heavy oil and the lubricant to form a flow stabilizing skin.

“Yield stress fluids — think toothpaste or hair gels — act as a solid if the applied stress is less than its yield stress (point at which a material begins to deform),” said Parisa Sarmadi, a doctoral candidate working with Frigaard. “Our idea is to maintain this layer completely unyielded, so the interfacial layer of the fluid acts as a solid. This eliminates interfacial instabilities.”

Another key concept involved in this work is interface shaping. “We can control the inlet flow rates in a way to shape the interface as we desire,” said Sarmadi. “The shaped interface generates pressure within the outer layer, and these pressures act to counterbalance the core buoyancy to center the core fluid. Typically, the transported oil is less dense than the lubricating water.”

For this work and previous studies, the researchers showed the VPL technique can be optimized to meet a system’s specific requirements. They also discovered that the yield stress required for these applications is easily attainable with available fluids.

This means that for any operational inputs, flow rates, geometries and fluid properties, the VPL technique can be optimized based on pump power, generated force and required yield stress. “The ability to shape the yield stress fluid came as a big surprise to us,” said Frigaard. “But effectively any shape can be imposed on the interface if the flow rates are properly controlled and there’s enough yield stress.”

Story Source:

Materials provided by American Institute of Physics. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
ScienceDaily

NASA’s Curiosity Rover finds an ancient oasis on Mars

If you could travel back in time 3.5 billion years, what would Mars look like? The picture is evolving among scientists working with NASA’s Curiosity rover.

Imagine ponds dotting the floor of Gale Crater, the 100-mile-wide (150-kilometer-wide) ancient basin that Curiosity is exploring. Streams might have laced the crater’s walls, running toward its base. Watch history in fast forward, and you’d see these waterways overflow then dry up, a cycle that probably repeated itself numerous times over millions of years.

That is the landscape described by Curiosity scientists in a Nature Geoscience paper published today. The authors interpret rocks enriched in mineral salts discovered by the rover as evidence of shallow briny ponds that went through episodes of overflow and drying. The deposits serve as a watermark created by climate fluctuations as the Martian environment transitioned from a wetter one to the freezing desert it is today.

Scientists would like to understand how long this transition took and when exactly it occurred. This latest clue may be a sign of findings to come as Curiosity heads toward a region called the “sulfate-bearing unit,” which is expected to have formed in an even drier environment. It represents a stark difference from lower down the mountain, where Curiosity discovered evidence of persistent freshwater lakes.

Gale Crater is the ancient remnant of a massive impact. Sediment carried by water and wind eventually filled in the crater floor, layer by layer. After the sediment hardened, wind carved the layered rock into the towering Mount Sharp, which Curiosity is climbing today. Now exposed on the mountain’s slopes, each layer reveals a different era of Martian history and holds clues about the prevailing environment at the time.

“We went to Gale Crater because it preserves this unique record of a changing Mars,” said lead author William Rapin of Caltech. “Understanding when and how the planet’s climate started evolving is a piece of another puzzle: When and how long was Mars capable of supporting microbial life at the surface?”

He and his co-authors describe salts found across a 500-foot-tall (150-meter-tall) section of sedimentary rocks called “Sutton Island,” which Curiosity visited in 2017. Based on a series of mud cracks at a location named “Old Soaker,” the team already knew the area had intermittent drier periods. But the Sutton Island salts suggest the water also concentrated into brine.

Typically, when a lake dries up entirely, it leaves piles of pure salt crystals behind. But the Sutton Island salts are different: For one thing, they’re mineral salts, not table salt. They’re also mixed with sediment, suggesting they crystallized in a wet environment — possibly just beneath evaporating shallow ponds filled with briny water.

Given that Earth and Mars were similar in their early days, Rapin speculated that Sutton Island might have resembled saline lakes on South America’s Altiplano. Streams and rivers flowing from mountain ranges into this arid, high-altitude plateau lead to closed basins similar to Mars’ ancient Gale Crater. Lakes on the Altiplano are heavily influenced by climate in the same way as Gale.

“During drier periods, the Altiplano lakes become shallower, and some can dry out completely,” Rapin said. “The fact that they’re vegetation-free even makes them look a little like Mars.”

Signs of a Drying Mars

Sutton Island’s salt-enriched rocks are just one clue among several the rover team is using to piece together how the Martian climate changed. Looking across the entirety of Curiosity’s journey, which began in 2012, the science team sees a cycle of wet to dry across long timescales on Mars.

“As we climb Mount Sharp, we see an overall trend from a wet landscape to a drier one,” said Curiosity Project Scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Pasadena, California. JPL leads the Mars Science Laboratory mission that Curiosity is a part of. “But that trend didn’t necessarily occur in a linear fashion. More likely, it was messy, including drier periods, like what we’re seeing at Sutton Island, followed by wetter periods, like what we’re seeing in the ‘clay-bearing unit’ that Curiosity is exploring today.”

Up until now, the rover has encountered lots of flat sediment layers that had been gently deposited at the bottom of a lake. Team member Chris Fedo, who specializes in the study of sedimentary layers at the University of Tennessee, noted that Curiosity is currently running across large rock structures that could have formed only in a higher-energy environment such as a windswept area or flowing streams.

Wind or flowing water piles sediment into layers that gradually incline. When they harden into rock, they become large structures similar to “Teal Ridge,” which Curiosity investigated this past summer.

“Finding inclined layers represents a major change, where the landscape isn’t completely underwater anymore,” said Fedo. “We may have left the era of deep lakes behind.”

Curiosity has already spied more inclined layers in the distant sulfate-bearing unit. The science team plans to drive there in the next couple years and investigate its many rock structures. If they formed in drier conditions that persisted for a long period, that might mean that the clay-bearing unit represents an in-between stage — a gateway to a different era in Gale Crater’s watery history.

“We can’t say whether we’re seeing wind or river deposits yet in the clay-bearing unit, but we’re comfortable saying is it’s definitely not the same thing as what came before or what lies ahead,” Fedo said.

For more about NASA’s Curiosity Mars rover mission, visit:

https://mars.nasa.gov/msl/

https://nasa.gov/msl

Go to Source
Author:

Categories
ScienceDaily

Particles emitted by consumer 3D printers could hurt indoor air quality

Consumer-grade 3D printers have grown in popularity in recent years, but the particles emitted from such devices can negatively impact indoor air quality and have the potential to harm respiratory health, according to a study from researchers at the Georgia Institute of Technology and UL Chemical Safety.

For the study, which was published September 12 in the journal Environmental Science & Technology and sponsored by Underwriters Laboratories, Inc. (UL)., the researchers collected particles emitted from 3D printers and conducted several tests to gauge their impact on respiratory cell cultures.

“All of these tests, which were done at high doses, showed that there is a toxic response to the particles from various types of filaments used by these 3D printers,” said Rodney Weber, a professor in Georgia Tech’s School of Earth & Atmospheric Sciences, who led the research.

The study was part of multi-year research project aimed at characterizing particle emissions by the printers in a controlled environment and identifying measures that could be taken by both 3D printer manufacturers and users to reduce the potential for harm. While earlier studies had focused on quantifying the particles being emitted, this time the researchers looked more closely at the chemical composition of the particles and their potential for toxicity.

3D printers typically work by melting plastic filaments and then depositing the melt layer upon layer to form an object. Heating the plastic to melt it releases volatile compounds, some of which from ultrafine particles that are emitted into the air near the printer and the object.

In earlier research, the team found that generally the hotter the temperature required to melt the filament, the more emissions were produced. As a result, acrylonitrile butadiene styrene (ABS) plastic filaments, which require a higher temperature to melt, produced more emissions than filaments made of polylactic acid (PLA), which melt at a lower temperature.

To test the impact of the emissions on live cells, the researchers partnered with Weizmann Institute of Science in Israel, which exposed human respiratory cells and rat immune system cells to concentrations of the particles from the printers. They found that both ABS and PLA particles negatively impacted cell viability, with the latter prompting a more toxic response. But these tests did not reflect actual exposures

The researchers also performed a chemical analysis of particles to gain further insight into their toxicity and allow comparisons to toxicity of particles found in outdoor urban environments. The analysis — called oxidative potential — simulates the toxic response that an aerosol would have on cellular organisms.

“The toxicity tests showed that PLA particles were more toxic than the ABS particles on a per-particle comparison, but because the printers emitted so much more of the ABS — it’s the ABS emissions that end up being more of the concern,” Weber said. “Taken together, these tests indicate that exposure to these filament particles could over time be as toxic as the air in an urban environment polluted with vehicular or other emissions.”

Another finding of the study was that the ABS particles emitted from the 3D printers had chemical characteristics that were different than the ABS filament.

“When the filament companies manufacture a certain type of filament, they may add small mass percentages of other compounds to achieve certain characteristics, but they mostly do not disclose what those additives are,” Weber said. “Because these additives seem to affect the amount of emissions for ABS, and there can be great variability in the type and amount of additives added to ABS, a consumer may buy a certain ABS filament, and it could produce far more emissions than one from a different vendor.”

The study also looked at which types of indoor environmental scenarios emissions from a 3D printer would most impact. They estimated that in a commercial building setting such as a school or an office, better ventilation would limit the amount of exposure to the emissions. However, in a typical residential setting with less effective ventilation, the exposure could be much higher, they reported.

“These studies how that particle and chemical emissions from 3D printers can result in unintentional pollutant exposure hazards, and we are pleased to share this research so that steps can be taken to reduce health risks,” said Marilyn Black, senior technical advisor for UL.

In the meantime, some measures can be taken by operators of 3D printers to lessen their impact on air quality.

  • Operating 3D printers only in well-ventilated areas
  • Setting the nozzle temperature at the lower end of the suggested temperature range for filament materials
  • Standing away from operating machines
  • Using machines and filaments that have been tested and verified to have low emissions.

Go to Source
Author:

Categories
ScienceDaily

Swimming toward an ‘internet of health’?

In recent years, the seemingly inevitable “internet of things” has attracted considerable attention: the idea that in the future, everything in the physical world — machines, objects, people — will be connected to the internet. Drawing on lessons learned from studies on a variety of marine animals outfitted with sensors, researchers in a new perspective article in ACS Sensors describe how an “internet of health” could revolutionize human medicine.

Imagine a world where you could present your doctor with an entire year’s worth of data on your eating habits, heart rate, sleep-wake cycles, and biomarkers of health, all obtained non-obtrusively from wearable sensors attached to skin or clothing or contained in cell phones. These data could be correlated with information about the environment, such as airborne pollutants and geographical location, to evaluate risks for illnesses or perhaps even prevent them. Michael Strano and colleagues have decades of collective experience with biologging — tagging marine animals with sensors to gain ecological insights, ranging from feeding behaviors to migration. In this perspective article, they share insights from these experiences that could someday help scientists develop an “internet of health.”

Surprisingly, a sensor attached to an organism can potentially uncover new information about seemingly disconnected behaviors, the researchers say. For example, a jaw-motion sensor attached to a sea turtle’s mouth can provide data on the animal’s specific anatomy, but it might also reveal detailed information on the type of food and the duration of feeding, as well as how the turtle captured the prey and ate it. In a study referenced in this article, the researchers used sensors to track the motions of 23 species of marine animals for a decade. The animals’ movements revealed migratory patterns, which the researchers correlated with data on seawater temperature and photosynthetic and human activities to predict how habitats could shift because of climate change. The team emphasizes that each sensor forms a partial but incomplete picture of an organism’s physical state, necessitating the use of multiple sensors. As with animal studies, a challenge for human medicine will be developing comfortable sensors that don’t impact people’s behaviors, the researchers say.

Story Source:

Materials provided by American Chemical Society. Note: Content may be edited for style and length.

Go to Source
Author:

Categories
IEEE Spectrum

NASA Hiring Engineers to Develop “Next Generation Humanoid Robot”

It’s been nearly six years since NASA unveiled Valkyrie, a state-of-the-art full-size humanoid robot. After the DARPA Robotics Challenge, NASA has continued to work with Valkyrie at Johnson Space Center, and has also provided Valkyrie robots to several different universities. Although it’s not a new platform anymore (six years is a long time in robotics), Valkyrie is still very capable, with plenty of potential for robotics research. 

With that in mind, we were caught by surprise when over the last several months, Jacobs, a Dallas-based engineering company that appears to provide a wide variety of technical services to anyone who wants them, has posted several open jobs in need of roboticists in the Houston, Texas, area who are interested in working with NASA on “the next generation of humanoid robot.”

Categories
ScienceDaily

Using math to blend musical notes seamlessly

In music, “portamento” is a term that’s been used for hundreds of years, referring to the effect of gliding a note at one pitch into a note of a lower or higher pitch. But only instruments that can continuously vary in pitch — such as the human voice, string instruments, and trombones — can pull off the effect.

Now an MIT student has invented a novel algorithm that produces a portamento effect between any two audio signals in real-time. In experiments, the algorithm seamlessly merged various audio clips, such as a piano note gliding into a human voice, and one song blending into another. His paper describing the algorithm won the “best student paper” award at the recent International Conference on Digital Audio Effects.

The algorithm relies on “optimal transport,” a geometry-based framework that determines the most efficient ways to move objects — or data points — between multiple origin and destination configurations. Formulated in the 1700s, the framework has been applied to supply chains, fluid dynamics, image alignment, 3-D modeling, computer graphics, and more.

In work that originated in a class project, Trevor Henderson, now a graduate student in computer science, applied optimal transport to interpolating audio signals — or blending one signal into another. The algorithm first breaks the audio signals into brief segments. Then, it finds the optimal way to move the pitches in each segment to pitches in the other signal, to produce the smooth glide of the portamento effect. The algorithm also includes specialized techniques to maintain the fidelity of the audio signal as it transitions.

“Optimal transport is used here to determine how to map pitches in one sound to the pitches in the other,” says Henderson, a classically trained organist who performs electronic music and has been a DJ on WMBR 88.1, MIT’s radio station. “If it’s transforming one chord into a chord with a different harmony, or with more notes, for instance, the notes will split from the first chord and find a position to seamlessly glide to in the other chord.”

According to Henderson, this is one of the first techniques to apply optimal transport to transforming audio signals. He has already used the algorithm to build equipment that seamlessly transitions between songs on his radio show. DJs could also use the equipment to transition between tracks during live performances. Other musicians might use it to blend instruments and voice on stage or in the studio.

Henderson’s co-author on the paper is Justin Solomon, an X-Consortium Career Development Assistant Professor in the Department of Electrical Engineering and Computer Science. Solomon — who also plays cello and piano — leads the Geometric Data Processing Group in the Computer Science and Artificial Intelligence Laboratory (CSAIL) and is a member of the Center for Computational Engineering.

Henderson took Solomon’s class, 6.838 (Shape Analysis), which tasks students with applying geometric tools like optimal transport to real-world applications. Student projects usually focus on 3-D shapes from virtual reality or computer graphics. So Henderson’s project came as a surprise to Solomon. “Trevor saw an abstract connection between geometry and moving frequencies around in audio signals to create a portamento effect,” Solomon says. “He was in and out of my office all semester with DJ equipment. It wasn’t what I expected to see, but it was pretty entertaining.”

For Henderson, it wasn’t too much of a stretch. “When I see a new idea, I ask, ‘Is this applicable to music?'” he says. “So, when we talked about optimal transport, I wondered what would happen if I connected it to audio spectra.”

A good way to think of optimal transport, Henderson says, is finding “a lazy way to build a sand castle.” In that analogy, the framework is used to calculate the way to move each grain of sand from its position in a shapeless pile into a corresponding position in a sand castle, using as little work as possible. In computer graphics, for instance, optimal transport can be used to transform or morph shapes by finding the optimal movement from each point on one shape into the other.

Applying this theory to audio clips involves some additional ideas from signal processing. Musical instruments produce sound through vibrations of components, depending on the instrument. Violins use strings, brass instruments use air inside hollow bodies, and humans use vocal cords. These vibrations can be captured as audio signals, where the frequency and amplitude (peak height) represent different pitches.

Conventionally, the transition between two audio signals is done with a fade, where one signal is reduced in volume while the other rises. Henderson’s algorithm, on the other hand, smoothly slides frequency segments from one clip into another, with no fading of volume.

To do so, the algorithm splits any two audio clips into windows of about 50 milliseconds. Then, it runs a Fourier transform, which turns each window into its frequency components. The frequency components within a window are lumped together into individual synthesized “notes.” Optimal transport then maps how the notes in one signal’s window will move to the notes in the other.

Then, an “interpolation parameter” takes over. That’s basically a value that determines where each note will be on the path from its starting pitch in one signal to its ending pitch in the other. Manually changing the parameter value will sweep the pitches between the two positions, producing the portamento effect. That single parameter can also be programmed into and controlled by, say, a crossfader, a slider component on a DJ’s mixing board that smoothly fades between songs. As the crossfader slides, the interpolation parameter changes to produce the effect.

Behind the scenes are two innovations that ensure a distortion-free signal. First, Henderson used a novel application of a signal-processing technique, called “frequency reassignment,” that lumps the frequency bins together to form single notes that can easily transition between signals. Second, he invented a way to synthesize new phases for each audio signal while stitching together the 50-millisecond windows, so neighboring windows don’t interfere with each other.

Next, Henderson wants to experiment with feeding the output of the effect back into its input. This, he thinks, could automatically create another classic music effect, “legato,” which is a smooth transition between distinct notes. Unlike a portamento — which plays all notes between a start and end note — a legato seamlessly transitions between two distinct notes, without capturing any notes in between.

VIDEO: Using math to blend musical notes seamlessly http://youtu.be/gHBhMGbJHe8

Go to Source
Author: