jmts (u/jmts) - Readit News

jmts commented on Why does FM sound better than AM? johndcook.com/blog/2024/1... · Posted by u/zdw

I guess the crux here is the claim that "the effect of random noise is to amplitude modulate". Does anyone here understand why?

Ps I don't think analogies are helpful.

jmts · a year ago

AM reception is essentially the direct conversion of the strength (amplitude) of a given radio frequency into an audio signal. Any other noise present at the same frequency is added to the signal (superposition/interference) and therefore impacts the strength of that frequency at the receiver. Therefore it is impossible for the receiver to know whether the amplitude it received is just signal or is signal plus noise.

The claim 'the effect of random noise is to amplitude modulate' is probably not 100% correct, because to my understanding it's not actually performing modulation (the modulation happens at the transmitter but the noise happens between the transmitter and receiver), but it is impacting the amplitude at a given frequency and to a receiver this is impossible to know whether said change in amplitude happened before modulation (signal) or after modulation (noise).

jmts commented on Why does FM sound better than AM? johndcook.com/blog/2024/1... · Posted by u/zdw

tejohnso · a year ago

This seems great at first, but more so as an explanation of how AM and FM differ; one being by amplitude (brightness), and the other by frequency (color).

What I don't see is how it explains why one would work better than the other.

If the tree is blowing in the wind, and a leaf obstructs the entire signal, it doesn't matter whether it's a change in brightness, or a change in color. Either way, that information is lost by the blocked leaf. And if the entire signal is not lost, perhaps many leaves may have blocked the signal but some signal managed to get through, it doesn't matter whether the signal change was a change in brightness, or a change in color. Either way you're going to notice the change. So I don't see how this clarifies why FM is better. What am I missing?

I see from the article that "noise tends to be a an unwanted amplitude modulation, not a frequency modulation." In other words, the tree is providing an unwanted change in brightness. It never provides an unwanted change in color.

I guess the tree is able to dim the signal so much that it appears to be a deliberate signal change? Couldn't this be dealt with if you know the details of the tree's dimming ability?

jmts · a year ago

FM works better because it is easier to detect the change in frequency independently of any change in the amplitude.

I'm unsure of what the correct terminology would be, but (for my linear algebra brain) you could say something like, for FM the noise dimension is orthogonal to the signal dimension, while for AM the noise and signal dimensions are the same. Therefore for FM any change in amplitude in the noise dimension should be mostly isolated from the signal dimension, while it is essentially impossible to tell what is noise and what is signal for AM - you could probably do some radio equivalent of a differential pair in order to detect noise and remove it, but then why would you bother when FM has improved noise rejection anyway.

jmts commented on Optimizing a bignum library for fun austinhenley.com/blog/big... · Posted by u/azhenley

parentheses · 2 years ago

I am so surprised that there's no exploration of Karatsuba's algorithm. That's what makes the Python implementation perform.

I actually came here hoping to find discussion on Karatsuba. https://en.m.wikipedia.org/wiki/Karatsuba_algorithm

jmts · 2 years ago

Please see the section titled "Faster multiplication"

jmts commented on DOS game “F-15 Strike Eagle II” reverse engineering/reconstruction war stories neuviemeporte.github.io/c... · Posted by u/LowLevelMahn

khaki54 · 2 years ago

Custom os?

jmts · 2 years ago

My understanding of PC game development at the time was that most games would re-implement their own drivers for system hardware, hence why you would often need to select what kind of graphics card, sound card, and their settings during the setup. As such, a game running from a boot disk is closer to just skipping DOS and having no OS rather than implementing a custom OS, although from another perspective you might just say that the game is the OS.

jmts commented on Oi (Interjection) en.wikipedia.org/wiki/Oi_... · Posted by u/userbinator

juliangamble · 2 years ago

Aussie Aussie Aussie!!!

jmts · 2 years ago

Oi Oi Oi!!!

jmts commented on Psytrance Guide psytranceguide.com/... · Posted by u/turrini

sebosp · 2 years ago

Laugh all you want, when I was like 12 years old my family was into this weird techno-pseudoscience-cult of "Ramtha's school of enlightenment" and they have the biggest trance/shamanistic playlists, we had these long ceremonies of hours of dancing while listening to music like this and drinking red wine and smoking tobacco on pipes. I guess if it wasn't for the alcohol I would have remembered all these amazing songs but well... I think that sect is still alive and I wish they had a playlist somewhere outside their website coz I can't stand the website much due to the religious content bringing back drunk memories. If you know of such a playlist please share

jmts · 2 years ago

Ramtha's School of Enlightenment used to come to a university I used to work at between sessions while the students were away. They would have a section of paddock fenced off and would wander around it blindfolded making "PSSHHTT" noises to stop running into each other (I assume). They definitely seemed like a peculiar bunch.

jmts commented on Motorbike crashes: highside and lowside crashes explained driverknowledgetests.com/... · Posted by u/molteanu

heyzk · 3 years ago

I'm confused about how a loose chain can cause the rear wheel to lock. Does the chain wedge between the rear sprocket and wheel?

jmts · 3 years ago

It's hard to tell what's actually happening in that clip. To me it looks like the chain is actually fully off the rear sprocket just before the rear locks up (it appears to have come off around 1:12). At that point in time the rear wheel should just be free spinning. It also appears to be free spinning during the highside, which is strange because I would expect the most likely non-rider-error issue in this case to be the chain binding between the rear sprocket and the swing arm.

I'm almost inclined to call that one rider error. Their general body language and control of the bike don't suggest to me that they're an experienced rider, and it almost looks like they've just panic-braked and locked up the rear, except it's an odd speed and place to have done that too.

jmts commented on ValueObject (2016) martinfowler.com/bliki/Va... · Posted by u/ksec

gepardi · 4 years ago

I really wanna understand this but I feel like it’ll take me a while.

jmts · 4 years ago

Programming is all about abstractions and the ways they interact. Specifically this article talks about what it means for two instances of an object to be "equal", which depends very much on what kind of equal you care about.

Consider the possibility that you order two laptops from your favourite computer store. When you order them, you customise one, then in the shopping cart you hit "+1" to order two of them, so for the purposes of this example they are functionally equivalent. When they arrive though, they have different serial numbers ABC, and XYZ. So then we start asking the question, are they equal?

One way of asking this question is "Do these two things perform the same function?" to which we can answer yes, ABC and XYZ perform the same function - this line of questioning treats the laptops as ValueObjects as described in the article - laptop ABC and laptop XYZ can be swapped for each other without concern about whether they will behave differently.

Another way of asking this question is what amounts to something closer to "Is this thing the one that I care about?". This line of questioning treats the laptops as ReferenceObjects. You've just received both laptops, taken them both out of the box, they're functionally identical except that you've decided that you want to use ABC for work stuff, and XYZ for personal stuff, and now you have some work stuff to do. You pick up one laptop and ask "Is this laptop ABC?" - not because the function of the laptops matter at this point, but now because of what they represent.

Both have their pros and cons (as described, ValueObjects are better when they are immutable, ReferenceObjects might tend to be more complex), and different languages make different choices about whether certain language primitives and standard objects/classes are implemented as ValueObjects or ReferenceObjects, but understanding them both conceptually allows you to write code that forces one kind of behaviour because that's what matters most for your chosen solution, independently of what the language you are writing it in has as its standard behaviour.

jmts commented on Difference Between Fault Tolerance, High Availability, Disaster Recovery (2014) pbenson.net/2014/02/the-d... · Posted by u/chynkm

notacoward · 6 years ago

When I was working in this area during relatively early days, the difference was sometimes expressed this way:

* Fault tolerance: near-infinite MTBF

* High availability: near-zero MTTR

With HA there is a blip. It might not be visible to an application because of retries, but it is visible outside of the HA system/component to some degree.

Special bonus thought: as a guide to designing or implementing an HA/FT system, I always found it helpful to think in terms of what happens to system reliability as size increases. In a traditional system, system reliability goes down because of dependencies between nodes/components. In some systems this degradation is even worse than you'd think because it's tied to the number of connections - O(n^2) rather than O(n). In an HA system, system reliability should go up because of nodes being able to cover for each other.

The key question was always: if X fails, what other part of the system can make up for (not just survive) it? If it's a whole node, what other node(s) can take its workload? If it's a disk, where is another copy of the data? If it's a network, how else can nodes communicate or at least synchronize? That last was interesting but because it led to things like serial lines or pinging through shared disks as a last-resort way to convey cluster state. Fun times.

jmts · 6 years ago

MTBF: Mean time between failures

MTTR: Mean time to repair