Hacker News Reader

Comment by amelius | Hacker News Reader

Doesn't the finite size imply that they are in fact repeating?

In this case they're probably recordings, but you could imagine that they'd be procedurally generated in which case not necessarily. A call to `Math.random()` is a finite length 'file' but won't repeat.

A call to Math.random() will in fact repeat eventually. The backing PRNG has a finite period.

Yeah, after it loops in several hundred years and I hear a pattern I've already heard, I'll be really annoyed!

The human brain is also finite, so even a true infinite random sequence would give the listener finitely many states.

So it doesn't matter whether a sequence is finite or not.

It may be partly affected by fully random effects such thermal noise, meaning there will be no period.

Good ones are loopable so there is no discontinuity when they repeat.

And the size of those files implies they are probably minutes in length, at the very least, so you probably don't notice the repetition.

Yes. I can detect repetition of ocean “white noise” if the length is too short. But a long enough track is just fine

Not necessarily.

In theory one can construct a chaotic (this is a precise definition) function with very little data that could replicate that class of noise with finite data.

Infinite lists are also another beautiful construct in lazily evaluated languages.

Not at a fixed rate with finite computing power or finite memory. Essentially a fixed algorithm needs ever increasing or infinite levels of precision in it’s calculations to avoid loops.

So like emitting 1, 0, 1, 1, 0, 1, 1, 1, 0, ...?

Doesn't need much to generate. It would need a wide counter but a MB is a lot of bits.

> Not at a fixed rate with finite computing power or finite memory. Essentially a fixed algorithm needs ever increasing or infinite levels of precision in its calculations to avoid loops.

If you start talking about true “infinity” then sure. You need to store enough state (or if you like, receive some input) for your computed output to be unique. And counting to infinity takes infinite amounts of memory. Infinity is not accessible to humans, and is best thought of as a thought experiment rather than a part of empirical reality.

But if you do 44kHz samples, a counter stored in a 32-bit integer that ticks up once per sample is enough state to give you all unique [i.e. non-looping] samples for about a day. A 64-bit integer will give you all unique samples for 13 million years. With a 75-bit integer you can get all unique samples for longer than the history of the universe so far.

So in practice, the “increasing” amount of memory required doesn’t (necessarily) grow fast enough to worry about.

Can prime numbers be used as lengths/periods so that there is no perceptible repetitions.

I saw this trick and used it to animate different parts of an animation (each part every p frames, where p is a prime) and it works very well.

Reply on news.ycombinator.com