These are just scratch notes that I took a while back.

Title: Digital signal processing lecture
Lecturer: WB7ABC
Host: Columbia Amateur Radio Club
Location: Columbia, MD
Date: 7/25/00 19:30-20:30 

Law enforcement carrying some sort of recording device on them each time they step out of the car.

Differences from the ham world:

• Have to maintain a chain of custody
• Mostly recorded materials
• Has a variety of sound problems, even on the same tape, where they go from place to place

These digital filters cost on the average of $16,000.

ATF gets called out to determine the cause of most large arson cases, including Ellicott city. They'll assist any state and local agency. Sometimes they'll find the survelance system and they have to recover the images.

Tools similar to Photoshop for image contrast.

The tape hardly ever melts as quickly as the rest of the case. The shell melts, but everything inside is probably in pretty good shape.

Tape authenticity, matching tapes to tape recorders. Spectrum analyzer, look at the tape physically, to match with recorders. Same materials that are used to align heads can be used to determine where the tape came from.

Voice identification can be done much more accurately by people than computers. You can do it through computers, might be 80 to 90% accurate, but the identification in court by a person in the conversation is much more valuable.

Why would it have 60 cycle hum if the recording was supposed to be made on a recorder with batteries.

200 to 3700 Htz recordings are considered good audio in the business. 2.4 cm/s and 1.2 cm/s. People use it because they're cheap. You narrow the bandwidth. 1.8 - 2 (units) with the slower speed. 55 dB typical range for analog, typical digital range goes up to 96 dB.

Every time something in the environment changes, the range changes.

200 to 3700 Htz considered to be wideband by amateur people. Narrower bandwidth, better the range is likely to be. Coming from an RF device with RF noise and characteristics.

DSP allows you to draw the filter shape that you want.

Tiny little tapes that store 45 minutes of 16 bit digital audio per side. It's about 1.5 by 1". Sony NTC-90.

Digital photographics, scientific working group on digital evidence. How do you handle the ease of editing digital photographics. They came up with the definition of what digital evidence is. How is the information stored and see if you can use that to show that it hasn't been altered, and edited by another machine.

Implementation of digital audio and video with digital signatures to prevent altering?

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