Ear Witness

For anyone not in NZ, a major court case finished recently with a jury over turning a previous multiple murder charge involving the deaths of 4 members of a family, and while ‘justice’ is always a debateable concept (often more clearly defined by the ability to spend a small fortune on legal aid and/or a QC) one piece of evidence was suppressed from the jury & while I wouldn’t normally be overly interested, this piece of evidence was audio – a recording of the phone call made to emergency services. Have a listen:

The issue here, is not so much what he actually said, but how prior knowledge alters the way you interpret what you hear. You only ever get one first impression & if you have any prior knowledge at all of what may or may not have been said, then that first impression is lost and it is on those grounds the ‘evidence’ was suppressed. One of the TV News shows consulted a forensic speech scientist, Dr Philip Rose, on the matter:

It is fascinating to me how perception can be altered, the McGurk effect is an obvious example, watch the following clip & establish what you are hearing, then replay it with you eyes shut:

There is a great article in the NYTimes about the concept of ‘Ear Witnesses’ and it explains similar phenomena: “If you ask people to count the number of times that a light flashes, and you flash the light seven times together with a sequence of eight beeping tones, people will say the light flashed eight times. When confronted with conflicting pieces of information, the brain decides which sense to trust…. on matters that demand a temporal analysis, and making sense of similar sounds in a sequence, the brain reflexively counts on hearing.”

Why is this? According to Barbara Shinn-Cunningham of Boston University; “The temporal resolution of our vision is an order of magnitude slower than what our auditory system can cope with.”

Audio Forensics is an intriguing aspect of audio, technology & perception, and while it reminds me of that great film The Conversation these people work on real life situations with potentially far reaching ramifications. While clarifying what is actually present in a sound recording is an obviously essential process, authenticating the actual location of the recording can also be vitally important. This article from Wired outlines some of the lengths forensic audio engineers go to: “Catalin Grigoras, a forensic examiner from Bucharest, told the workshop how he uses the frequency signatures of local electrical power sources to pinpoint when and where recordings were made. According to Grigoras, digital recorders that are plugged into electrical sockets capture the frequency signature of the local power supply – a signature that varies over time.
Working with electrical companies throughout Europe, Grigoras has compiled a database of power signatures spanning several years. He uses a software package called DCLive Forensics to compare the power signatures captured on suspect recordings with the signatures stored in his database. That, in turn, allows him to determine when (and, to some extent, where) the recordings were actually made.
The technique can even be applied to recordings made with battery-powered recorders, as long as they use electret microphones. Because they act like capacitors, electret mikes will register the electrical signatures of nearby devices. In one case, Grigoras claims to have identified the date of a recording broadcast in Europe, but made in the Middle East, “probably in the mountains, or in a cave,” he says. He didn’t mention any names, but it was hard not to think of Al Qaeda. Grigoras holds a Ph.D. in electrical engineering and performs forensic work for the Romanian ministries of justice and the interior.”

As they say, the truth will out – even if it needs some seriously high tech help!

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