Periodic noise

Please use headphones. Mediocre PC speakers might spoil the effect.

• The first demonstration is 10 seconds of normal white noise (8 bit mono, 20 kHz: 196 kB). This is just to show you that the effects you will hear in periodic noise are not inherent in the noise itself.

The random numbers for this noise are simply the 200,000 first digits of  (compare also FAQ). Please note that a zero sound amplitude corresponds to 0x80 in WAV files, so the actual bytes stored in the WAV file are 0x83 0x81 0x84 0x81....

• The next demonstration is 10 seconds of periodic noise (196 kB) with a cycle length of 500 ms. You will easily detect the rhythm. This is not an artifact due to the cut-and-paste technology of periodic noise (see FAQ). It is your echoic memory that tells you that something is repeating.

This noise was made by repeating the first 10,000 digits of  twenty times.

• Other samples of periodic noise sound different: Click on the different  symbols    

These four periodic noises are all built from 10,000 digits of , repeated twenty times. The difference to the above noise of  is that they don't start with the first digits (i.e. with 3, 1, 4, 1...). Instead, 10,000, 20,000, 30,000 or 40,000 digits are skipped before recruiting 10,000 digits.

• Longer cycles give more details. Here are 10 seconds of 1-s periodic noise (196 kB). You might wish to listen to it repeatedly.The longer one listens to periodic noise the more detailed the percepts. Just in case you have a fast and cheap line: Here are 20 seconds of the same 1-s periodic noise (391 kB).

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• Here are 20 seconds of a semiperiodic noise (compare FAQ, 391 kB). Only 200 ms of the 800-ms cycle are kept constant, the other 600 ms are always a different piece of noise. It is a little bit more difficult to detect the regularity. If you don't get it you are allowed to cheat: here are 10 seconds of a 300-ms semiperiodic noise (196 kB) with the same constant reoccurring 200-ms segment as above (and only 100 ms variable noise in-between). You can “train” yourself with the shorter rhythm; it is much easier to get the segment there. And then you can switch back to the 800-ms cycle. Now it should be obvious. You've got the rhythm?