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June 2, 2005
Have The Grewal Tapes Been Altered?

The Globe & Mail updated its report on the Grewal tapes a short time ago with the news that an audio expert says that the tapes show an "abnormality" that could indicate tampering:

Stevan Pausak analysed a 46-second segment of the recordings and says there's a break in it that indicates a portion may have been cut out.

He says the abnormality occurs in a recorded phone chat between Mr. Grewal and Health Minister Ujjal Dosanjh in which they discuss future job prospects for the MP in exchange for crossing the floor.

He says there is a discontinuity in the audio file, what he calls a zero-signal gap of about 0.3 seconds. The signal goes abruptly to zero in that interval, and afterward it continues.

I'm not an audio expert, but I do work with audio files as part of my job. The zero-signal artifact could mean that an audio sample has been cut or erased, as Pausak states. However, on voice-activated recording equipment, which one frequently finds in telephone recording systems, zero-signal artifacts are common. They occur when the voice levels drop so low as to deactivate the recording, and then the machine senses the someone speaking again. It's the bane of investigators everywhere, precisely because it makes the sound on the audio appear artificially choppy. It's one reason I switched to a system that sensed an off-hook condition for automatic recording instead of the voice activation system.

I would suspect that such a short dead-air space indicates the equipment had trouble sensing the voice rather than any foul play. Of course, other artifacts may be found that drive investigators to another conclusion, but if that's all they find unusual about these tapes, it doesn't sound like much of a problem to me.

One question I would ask is whether the tapes that Grewal produced were the original tapes from the recording or whether he copied the conversations off to another media. If it's the former, it's almost impossible to alter source tapes in the manner that Martin and Dosanjh suggest. If the latter, anyone with a digital editor could have accomplished it.

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Posted by Ed Morrissey at June 2, 2005 6:30 PM

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» Grewal tapes spliced? from Stephen Taylor - Conservative Party of Canada Pundit
Tonight there are allegations from the Liberals that the tapes are spliced and doctored to make the attempted bribery of Gurmant Grewal seem... um... a lot... worse? You can't blame the Liberal spin though; this is a logical path to take while runni... [Read More]

Tracked on June 2, 2005 9:34 PM

» They've been altered! from Black Sheep Press
On CBC this evening they were reporting about how they had a forensic audio expert listen to a copy of the Grewall tapes and his conclusion was that they might possibly have been altered but it couldn't be proven. The exact phrase I believe was that ... [Read More]

Tracked on June 3, 2005 12:34 AM

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