| MadSci Network: Engineering |
Robin, I feel your pain. First, external magnetic fields can mess up audio tapes as well as floppy disks and other types of magnetic storage (such as hard disk drives). So, I hope you have thrown away that purse because if this problem happened once, it will happen again. Magnetic fields are present around all permanent magnetics, such as those found in speakers, headphones, and the shake-to-recharge LED flashlights. Put anything like that in your purse with the magnetic recordings and you are asking for more trouble. I submitted your question to John Goldfarb of the National Institute of Standards and Technology in Golden, Colorado (see http://www.boulder.nist.gov/div818/81803/2001/MagneticRecordingMeasurements/index.html). He provided the following thoughts: "From her description it appears that Robin's tape was only partially erased by the permanent magnet. The analog audio signal should be recoverable and restorable by a commercial data recovery company. The company selected should have expertise in analog signal manipulation: filtering and amplification. In requesting a cost estimate, she should advise the company whether the problem is actually more serious: unintelligible speech, not merely fluctuations in sound level." The normal rules for recovering damaged media apply: 1. The first rule is to do no harm. For some types of tape damage (wet tape, tape that is sticky, tape that has been exposed to fire or smoke), playing the tape can cause further damage and limit the potential for recovering your data. 2. This is not a do-it-yourself job. You are going to have to hire a professional to salvage the tape recording, and it is going to cost some money. An audio recording is made by changing the magnetic alignment in particles embedded in the magnetic tape. When you exposed the tape to an external magnetic field, some, most, or all of those particles had their alignment changed in response to the external magnetic field. From a practical standpoint, those magnetic particles have no memory of how they were aligned before being exposed to the field so you can't simply wave a magnet with the opposite polarity over the tape and have the damage reverse itself. In fact, exposing the tape to a second magnetic field would almost surely guarantee that the tape would be completely erased. If you look on the Internet for Magnetic Tape Recovery services, there are a number of commercial companies that specialize in data recovery. The National Archives provides a short list of companies that specialize in disaster recovery (see http://www.archives.gov/preservation/disaster-response/vendors.html), which is probably a good place to start. I am sorry that I can't offer a better solution. One last thought, though...have you thrown away that purse yet?
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