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Interesting table of varying frequency in Doom.exe and derivatives

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By using an audio editor like Audacity to import Doom.exe or derivatives such as Eternity.exe, under 11025Hz sample rate, 8bit unsigned sample and listening to it (warning, can be piercing), by about 51.5 seconds you'll start to hear a waving sound that lowers and raises in frequency.

Quite indeed, it's a data table whose row length varies smoothly, instead of being uniform, like with normal data tables. Also, its values also vary mostly between 0xFF and something greater than 0 that goes up in a sawtooth-like way.

Here's a picture of only a small part of the sound (table): http://i48.tinypic.com/2hqxttl.png

The table itself, in WAV format, can be downloaded here. I lowered its intensity a bit so as to avoid complaints. Here is an approximate copy of that sound. It's not exact, because I don't know how to extract it verbatim with what utilities I have, but it's good for a demonstration. You'll have to try importing DoOm.exe yourself if you want the real thing. http://www.speedyshare.com/files/23108114/Doom_table2.wav

The question of this thread: what's the purpose of that table in the exe? Both Doom and Eternity have it so far.

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You probably stumbled upon Doom's precalculated sine/cosine table. This is actually stored as a table of integers though, with excursion range -/+ 64K (so it would be 17-bit), but interpreting it as 32-bit integer signed will work too. The actual number of 32-bit samples is 10240.

The data endianness will probably play tricks on you depending on import settings.

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Heh, might work as an alarm clock sound...

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From the sound of it, it's probably the sine lookup tables or something similar. You'll probably find multiple sound patterns in the executables where there are tables of data.

Out of curiosity, what made you decide to open up doom.exe in Audacity? :)

Edit: Oops, shit. I should read all replies before replying myself!

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It's part of a SETI-in-reverse program, a pre-arranged signal that's radiated into space from millions of computers to tell the demons that dinner is ready. They'll arrive late December next year.

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Super Jamie said:

But dinner will be cold by then!

That depends on what hemisphere you live on. *goes off to check that the armoury is fully stocked*

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