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Digital Signal Processing

Copyright © 1999 by H. Paul Shuch, Ph.D.
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
email n6tx @ setileague.org

The audio output from the SETI receiver is mostly noise, both natural and artificially generated. If we are very lucky, there may be buried somewhere in that noise an intelligently generated signal of extra-terrestrial origin. But it's likely to be buried so deep in the noise that no human sense can detect it. To separate the cosmic wheat from the galactic chaff, we employ a technique known as Digital Signal Processing, or DSP.

The first step in the DSP process is to feed the receiver's audio output into the computer, in a form which the computer can recognize -- that is, as binary data. We need an analog to digital converter (ADC) to accomplish this, and the ADC of choice for amateur SETI is the PC Sound Card. Just about any SoundBlaster compatible audio card will work with The SETI League's signal analysis software. These cards sample an audio waveform 44,000 times per second. One of the rules of information theory is that to digitize a signal, it must be sampled no less than twice for every cycle at its highest frequency. With 44 KSPS (kilo-samples per second) sound cards, this means we can digitize and analyze audio components out of our receiver up to 22 kHz in frequency.

Once the audio signal has been digitized by the sound card, it is up to the SETI computer, and its associated software, to perform the required signal analysis.


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