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Spring 2013, page 2

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Comparing the unique pattern of the frequencies on an audio recording with a database that has been logging these changes for 24 hours a day, 365 days a year provides a digital watermark: a date and time stamp on the recording. Philip Harrison, from JP French Associates, another forensic audio laboratory that has been logging the hum for several years, says: "Even if [the hum] is picked up at a very low level that you cannot hear, we can extract this information." It is a technique known as Electric Network Frequency (ENF) analysis, and it is helping forensic scientists to separate genuine, unedited recordings from those that have been tampered with.

Dr. Harrison said: "If we have a recording we can extract the hum and compare it with the database, if it is a continuous recording, it will all match up nicely. If we've got some breaks in the recording, if it's been stopped and started, the profiles won't match or there will be a section missing. Or if it has come from two different recordings looking as if it is one, we'll have two different profiles within that one recording."

In the UK, because one national grid supplies the country with electricity, the fluctuations in frequency are the same the country over. So it does not matter if the recording has been made in Aberdeen or Southampton, the comparison will work. Elsewhere around the world, it is slightly more complicated because some countries can have two or more grids. But in these cases, all it takes is for the hum to be continuously logged on each power system and for a recording to be com-pared against each of them. Dr. Harrison said: "This has really been a key tool in the box to help us with this kind of work."

Crucial in court

Recently, Dr. Cooper was called as a witness on ENF in court for the first time. A gang were accused of selling weapons, and undercover police had recorded an arms deal. But the defence claimed that the police had tampered with the recording and had edited several separate recordings together to make their case. Dr. Cooper said: "The defence made the allegations and we were asked if we could authenticate the recordings. "We carried out various forms of analysis, including the mains hum frequency analysis and we found some good quality signals, and that the alleged date and times of the recordings matched with the extracted data from the recordings themselves."

The analysis revealed that the recordings had not been tampered with - and this proved crucial to the trial. The trio - Hume Bent, Carlos Moncrieffe and Christopher McKenzie - were found guilty and jailed for a total of 33 years for being involved in the supply of firearms. The Met Police were the first to automate the system, and Dr. Cooper says the technique is now starting to be used widely by this force, as well as others around the world. But even with advances like this, he admits there are always new challenges ahead. He says: "Digital forensics is constantly in flux, and the technology is changing every day. Every time a new format comes out, we need to be able to extract the data from those recordings and find different techniques to find out more about them."

Link to original BBC article

Chicks like consonant music

Psychological Science, October 2011, vol. 22, no. 10 1270-1273

Cinzia Chiandetti, Center for Mind/Brain Sciences, University of Trento and Giorgio Vallortigara, Department of Psychology, University of Trieste

Abstract:
The question of whether preference for consonance is rooted in acoustic properties important to the auditory system or is acquired through enculturation has not yet been resolved. Two-month-old infants prefer consonant over dissonant intervals,but it is possible that this

preference is rapidly acquired through exposure to music soon after birth or in utero. Controlled-rearing studies with animals can help shed light on this question because such studies allow researchers to distinguish between biological predispositions and learned preferences.

In the research reported here, we found that newly hatched domestic chicks show a spontaneous preference for a visual imprinting object associated with consonant sound intervals over an identical object associated with dissonant sound intervals. We propose that preference for harmonic relationships between frequency components may be related to the prominence of harmonic spectra in biological sounds in natural environments.

Link to article


Dolphins imitate calls

Dolphin communication has been studied extensively. Their various clicks and squeaks are thought to be a sophisticated type of language. Dolphins are also known to have the capacity to imitate sounds, including other dolphins. But a new study by Dr. Vincent Janik, an Associate Professor of Biology at St. Andrews University in Scotland, has found out which dolphins they imitate and why.

Every dolphin has a signature whistle that is known to others in the same social group. When they become separated from each other in the ocean, a dolphin will imitate the sound of its mother's whistle, for example. It's a way of letting the other dolphin know they are near, similar to a human shouting out the name of a person they are trying to locate.
Link to CBC article


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