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Ask HN: Teach me something new

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Re: Ask HN: Teach me something new

#241

Post by reom_tobit »

vermarish wrote: post #225

An electric guitarist usually has a pedalboard that they use to make different guitar tones. Let's approach this like an electrical engineer might. Time is a straight arrow: call it t. The guitarist plays, and their guitar pickup records a signal. At any time t, measure the value of this signal's waveform: call it x. That signal can go into a pedal that maps each value to create an output signal. Call it f(x, t). The…

> Another cool thing about LTI systems is that when you chain multiple of them together, the order does not matter. Reverb, delay, EQ, and wah are all LTI.

Delay and reverb may be LTI in your definition, but they very much do matter what order they are in, every time.

Delay before reverb is going to give a more staccato sound, whereas the reverb before delay is probably just going to wash the whole thing out if you’re not careful on your settings.

Great comment otherwise!

Re: Ask HN: Teach me something new

#242

Post by _zywo »

thinkingemote wrote: post #73

People have always and will always think that the time they are living in is the most important time ever. This is a self evident fallacy or a universal truth. These times we are living in are not the most important. Or, of they are, then everyone everywhere is at everytime living at the same importance. Now, there is something called the hinge of history that some mathematicians have looked into the chance of "well…

My life may not be the most important time to other people, but it is the most important time to me. Importance is relative.

Re: Ask HN: Teach me something new

#243

Post by remus »

onion2k wrote: post #203
kretaceous wrote: post #17

Take a positive integer. If it's odd, multiply it by 3 and add 1. If it's even, divide it by 2. Example: 7-22-11-34-17-52-26-13-40-20-10-5-16-8-4-2-1-4-2-1-4-2-1... Any positive integer you take, you end up in a 1-4-2-1 loop. It's not proved yet but there's no number found yet that satisfies otherwise. That's the Collatz Conjecture or the 3n+1 problem. Probably the easiest conjecture to explain to someone. Good day/n…

Presumably there's a reason why it's hard to prove either true or false, right?

Depends what you mean by a good reason I guess. A lot of very capable mathematicians have put time in to the problem and it's proven to be pretty resistant to a solution. I think problems like this often feel a little incongruous because they are so simple to state but so hard to solve.

Re: Ask HN: Teach me something new

#244

Post by sph »

SemanticStrengh wrote: post #122

Very few people know the potent facts about the brain: * your neurons are not in your "brain" 90% of your neurons are not in what you generally denote by brain. They are in your cerebellum. The cerebellum has a distinct neural architecture, that difference is in fact clearly visible with the najed eye. A very poor simplistification would be to call it our GPU. * the spinal cord is huge and is structurally a contiguou…

> your neurons are not in your "brain" 90% of your neurons are not in what you generally denote by brain. They are in your cerebellum.

Excuse the dumb question, but what's in the brain then? Or are you meaning to say that the cerebellum has a much higher density of neurons than the brain?

Re: Ask HN: Teach me something new

#245

Post by vnorilo »

mikelevins wrote: post #49
krasotkin wrote: post #43

Earlier quoted context omitted.

I have experienced this several times and almost never have a headache. I definitely can't read what's beyond/obscured by the scotoma. The first time it happened was during a test in high school and the splotch grew until I was forced to read the questions in my peripheral. I have an anecdote that corroborates your observation that cognitive experiences are more complicated then assumed: I was once very, very sleep d…

Do me a favor some time and try to read through the scotoma, if you remember to. I think that I would have just assumed I couldn't do it if I hadn't been reading something really interesting when the scotoma started. It's only because it came on while I was already reading that I discovered that I was able to continue. If you remember to try it, the results will be interesting no matter which way they turn out.

I have migraine once or twice a year, and the most recent attack indeed interrupted my reading, quite simply did not see the letters through the zigzag. As it gradually covered the focal point of my vision I was trying to "squint" mentally but eventually gave up. There was no followup headache, just a slight vertigo.

Re: Ask HN: Teach me something new

#246

Post by elric »

CGamesPlay wrote: post #219
mikelevins wrote: post #28

I've described this on HN before; forgive me if you've already seen it. I have chronic migraine. It sounds worse than it is; I rarely suffer attacks anymore, and when I do, they're usually mostly harmless, as in the case I'll describe below. Contrary to popular belief, migraine is not a headache. It's something a little more like an epileptic seizure. Intense headaches are one common symptom, but there are a lot of o…

Interesting. I get these scotomas about every 6 months or so, usually lasting for 30 or so minutes. I was told they were called "ocular migraines", and a cursory glance over the internet doesn't seem to help me differentiate between the two, although I will say that [0] is a very accurate depiction of how it looks when it happens to me. I normally just take a break from whatever I'm doing and go for a walk. The first…

(another migraineur chiming in here)

It's a common misconception. What you're calling "ocular migraines" are more accurately referred to as "migraines with aura without headache", sometimes called "silent migraines". You can get actual ocular migraines as well, but those affect the eye (or optic nerve), and as such, are limited to the eye. Scintillating scotomas caused by migraine auras are visible with your eyes closed, and look the same in both eyes.

Re: Ask HN: Teach me something new

#247

Post by _zywo »

arnarbi wrote: post #115

xp is a quick way in vi to swap two adjacent characters (a common typo correction) Ctrl-T does the same in emacs, and also in readline based programs like bash, as well as everywhere on macOS.

> xp

I always thought the fact that Vim had automatic buffer copying and forced me to use "0p instead of p was really annoying. Looks like there is an actual reason for it after all :)

Re: Ask HN: Teach me something new

#248

Post by mongol »

Timwi wrote: post #159
tailung wrote: post #111

Earlier quoted context omitted.

well, I think that if you are aware (mindfulness) about your thought patterns you can steer them, and usually what you think you become, because your thoughts drive actions. In my personal experience practicing self awareness has helped with this. I understand that there are factors outside of our control, but what goes on within us can be controlled to some extent with effort and time.

You cannot control physics though. What goes on in your brain is entirely just physics. We have a subjective impression of control, but that too is only the result of physics.

There is more to it than just "physics". I find the "Orchestrated objective reduction" hypothesis by Penrose and Hameroff interesting in this regard

Re: Ask HN: Teach me something new

#249

Post by Engineering-MD »

vasco wrote: post #120
leephillips wrote: post #101

By far the most important martial arts skill is the ability to function effectively after receiving a powerful blow to the face, solar plexus, etc. The only way to develop this skill is by practicing it; very few people do, for obvious reasons. If your martial arts training does not include this, it may have many benefits, but is severely lacking as training for actual fighting.

My teacher used to say the most important martial arts skill for real life is predicting a fight and turning around and running away.

I always thought this, but only works if you are alone, or the person you want to protect can run too. Fighting is most useful to defend someone else who can’t run or fight.

Re: Ask HN: Teach me something new

#250

Post by SteveGoob »

Programmatically determining the region of an AWS EC2 instance using the metadata API was very annoying in the past; there was no endpoint for it. Instead, devs used many methods to determine the region[1], primarily by dropping the last letter off of the availability zone, (e.g. `us-east-1a` -> `us-east-1`) which was queriable.

At this point, AWS has updated the API to allow querying for the region as one would expect. See my answer on the afore-footnoted question[2].

[1] The number and variety of answers on the topic is both hilarious and terrifying: https://stackoverflow.com/q/4249488

[2] https://stackoverflow.com/a/62664161

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