matthiasl · HackerTrans

matthiasl

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Decoding the telephony signals in Pink Floyd's 'The Wall'

corelatus.com

417 pointsby matthiaslvor 2 Jahren131 comments

Plotting GPS data extracted from millions of Flickr photos to generate a map

cs.cornell.edu

4 pointsby matthiaslvor 17 Jahren0 comments

comments

vor 4 Monatendiscuss

"What is the mechanism that increases risk for MOV-sourced fires in this arrangement?"

I wondered the same thing, and failed to find a satisfying explanation.

I can find plenty of reports of MOV fires, especially in situations where there's a persistent over-voltage, e.g. a 120 V site actually having closer to 240 V due to a floating neutral. But I don't see how chained MOVs make that worse in general. This blog post has some nice photos:

https://www.electrical-forensics.com/SurgeSuppressors/SurgeS...

vor 5 Monatendiscuss

It took me a while to realise that you were responding to the article, not a comment here.

You're right in correcting the article, but I'd like to add that for probably around a decade, Erlang had 'sender punishment', which is what 'IsTom' who replied to you is probably talking about.

Ulf Wiger referred to sender_punishment as "a form of backpressure" (Erlang-questions mailing list, January 2011). 'sender punishment' was removed around 2018, in ad72a944c/OTP14667. I haven't read the whole discussion carefully, but it seems to be roughly "it wasn't clear that sender punishment solved more problems than it caused, and now that most machines are multi-core, that balance is tipped even more in favour of not having 'sender punishment'".

vor 9 Monatendiscuss

Right, it's TX-only. The article says so explicitly halfway through:

"As before, this is a transmit-only proof of concept"

I didn't notice that on my first reading.

vor 11 Monatendiscuss

> All the designs I know of have a pumped (active) cooling loop for the reactor, then a secondary loop where the coolant (typically water) evaporates and drives a turbine, [...] You don't want potentially radioactive water to interact with your turbine directly, makes it a nightmare to maintain

A "Boiling Water Reactor" (BWR) has the reactor and the turbine on the same cooling loop. The radioactivity in the water going through the turbine is not a "nightmare", it is a manageable trade-off.

Some major currently-operating BWRs are Leibstadt (Switzerland, 1.2 GWe), Oskarshamn (Sweden, 1.4 GW) and several dozen in the USA. Germany also had some, they were shut down a few years ago (e.g. Grundremmingen).

https://www.gevernova.com/nuclear/carbon-free-power/large-re...

vor 2 Jahrendiscuss

Assuming you're refering to Hövding, the recall was overturned on appeal, back in 2023, but the company went bankrupt anyway:

https://discerningcyclist.com/hovding-bankruptcy/

In some types of crashes, the Hövding had better crash performance than ordinary helmets. In others it performed worse.

More generally, it may be that someone comes up with a design which incorporates inflatable sections which is more successful.

vor 2 Jahrendiscuss

I looked at a London telephone book from 1979, when I think the record was released.

Most of the phone numbers were something like 01 361 1234, i.e. seven digits after the 01 area code. The _361_ part was bold, so I think that was an exchange number.

A few numbers were something like "Placename 12345". Wikipedia explains why that was.

vor 2 Jahrendiscuss

(Author here) No contradiction.

I think what happened is

1. The recording engineer dialled the operator. Could have been pulse dialling, could have been DTMF, doesn't matter.

2. Operator answered and the engineer said "I'd like to call London, collect, number 01xxx831".

3. Operator entered 044 1 xxx 831, and this was transmitted to another exchange in SS5 tones.

I didn't grow up in the USA, but a couple of people who did have said that, yes, they think that at least some of the time, you could hear the SS5 tones and also the initial conversation between the operator and whoever answered the phone. It may be that it depended on the operator, since they probably had a mute button, and maybe on the particular exchange the operator was in.

In the film, we hear from 3 onwards.

vor 2 Jahrendiscuss

659 8890

That one's just ordinary DTMF. I recorded the audio, trimmed it manually and then made a spectrogram like this:

    sox gun1.wav -n rate 4k spectrogram -m -y 500

The 'rate' switch is to cut down on how much of the frequency space we can see. I left the audio as stereo because there's less music power on one channel, making it easier to see the tones.

(And google finds quite a few pages confirming those digits)

vor 2 Jahrendiscuss

You're right; I think CCITT5 is just another name for SS5, because different groups were writing standards. Bell called it one thing, CCITT (an international standards group) called it another thing. And then in the 1990s, the CCITT renamed itself to ITU.

vor 2 Jahrendiscuss

The discussion is new to me.

I started analysing the audio because someone sent me a link to the film (The Wall) on youtube and asked me about the signalling. Once I'd decoded the telephone number, I tried googling it, to see if someone else had already figured out what it was (a US local number? the number to a US operator? the number a US operator called to talk to a UK operator? the number a UK operator dialled to get a London number?), but nothing came up. There's quite a bit of good discussion about that in the comments here.

A week or two later, I tried googling 'Pink Floyd Telephone Call', and found that the audio actually comes from the album, i.e. it's not just in the film, and a bit more information about how it was made, and put that in the addendum.

vor 2 Jahrendiscuss

Interesting.

Normally, films use deliberately fictious numbers, e.g. in the US it's always xxx555xxxxxx. Wikipedia says the UK uses various area codes for the same thing, including 011x and 01x1. The Pink Floyd number is a bit unusual---it's not made up.

According to a previous analysis, the call was the album's "Chief Engineer James Guthrie who called his own London apartment", with a neighbour answering the phone. Someone probably knows roughly where James Guthrie lived in 1979/1980 and what the area code there was. But I don't.

vor 2 Jahrendiscuss

Author here.

Yep, 44 is the UK country code. The problem I got stuck on is that the rest of the number, 1831, didn't make sense. I assumed the number was complete, since it had the right start and stop signalling (KP1/KF).

It's not long enough to be a London telephone number, and, today, I think London numbers start with 020. The UK numbering plan has changed several times since 1980, but I couldn't find a time between 1980 and now where part of 1831 was a London number.

Later on (in the addendum), it turns out that others took a look at the signal in the time domain and spotted a splice, i.e. digits are chopped out of the middle of the number, so the area code probably isn't there at all. It could be that the area code starts with 1, and then the phone number ends with 831.

vor 3 Jahrendiscuss

There's no smoke coming out.

Best guess: you're confused by the word "smokestack". Smokestack is a synonym for chimney. The power station is closed. The chimneys are still there, but there's no smoke coming out of them.

vor 3 Jahrendiscuss

ATM cells have 48 byte payloads.

Supposedly that was because different groups involved in the standardisation process wanted either 32 or 64 byte payloads.

vor 3 Jahrendiscuss

Not important to the conclusion or reasoning... but Stevena's post says:

  "the whole team working on Erlang quit and started their own company."

The same event as described in "A history of Erlang":

  "In December, most of the group that created Erlang resigned
  from Ericsson and started a new company called Bluetail AB."
  https://www.labouseur.com/courses/erlang/history-of-erlang-armstrong.pdf

'most of the group that _created_ Erlang' is not the same thing as 'the whole team _working_ on Erlang'. Or, quantifying it, at the end of the 'history' paper, there's a list of 45 people under 'implementation' and 'tools'. Around 35 were at Ericsson in 1998. Of those, nine or ten quit to form Bluetail, and another two or three left for Bluetail later on.

(In 1998, there were two connected groups working on Erlang in the same building in Älvsjö, Stockholm. One was the computer science laboratory (CSLAB), where Erlang was created, the other was "Open Systems", which had more of a development role. A significant part of CSLAB left. Almost all of 'Open Systems' stayed. Many that stayed were already doing a stellar job on Erlang and many still are.)

vor 4 Jahrendiscuss

To put some numbers on "much worse" versus "not much worse":

The best window I can find from the major Danish manufacturer Velfac has a total U-value of 0.82 W/°K/m² [1]. It's a triple-glazed window with argon and coatings.

A typical insulated thin (100mm) wood-frame wall, i.e. the sort you'd use if you were building a summer house in Sweden has a U-value of 0.4 W/°K/m² [2], i.e. twice as good as the window above.

A typical rock- or glasswool insulated wood-frame wall for a modern year-round house has a U-value of 0.2 W or better, i.e. four times as good as the window above.

Wall that are so bad that they're roughly equivalent to the triple-glazed window above are something you'll mainly find in buildings from 50+ years ago, at least in Sweden. I expect Norway to be similar. [3]

'bjarneh' mentioned both triple- and quadruple-glazed windows. I've only seen quadruple used in noise-reduction applications, e.g. hotel next to a busy road. If you have a data sheet for one, it'd be interesting to see what the U-value is.

One of the posters above referred to 'R-value'. It's the reciprocal of the U-value. Wikipedia has good explanations of both, as well as typical values for windows and walls. [4,5]

References are mostly in Swedish, because the poster 'bjarneh' was talking about windows in Norway, so I wanted references for companies that actually sell things in Scandinavia.

[1] https://products-api.velfac.com/files/11644/VELFAC%20STANDAR...

[2] https://www.isover.se/hur-tjock-isolering-ska-man-ha-att-fa-....

[3] https://www.traguiden.se/konstruktion/konstruktiv-utformning...

[4] https://en.wikipedia.org/wiki/Thermal_transmittance

[5] https://en.wikipedia.org/wiki/R-value_(insulation)

vor 4 Jahrendiscuss

Schroedingersat> ...albedo increase...

You mean _decrease_, right?

vor 4 Jahrendiscuss

> Electric heat pumps actually don't work in very cold weather.

I think that statement needs to be qualified and quantified.

Qualified: your claim is probably only intended to apply to air-source heat pumps, not ground-source heat pumps. Ground-source heat pumps are popular in places with cold weather, for instance Sweden.

Quantified: If you mean -40°C, then, yes, air-source heat pumps aren't going to work. But most people don't live in places that cold, and just because we can't use air-source heat pumps in a few places doesn't mean they're useless everywhere. Here's a data sheet for a relatively cheap air-source heat pump that's rated to work down to -25°C (about -14 F):

https://img.polarpumpen.se/pfiles/fujitsu-km-slim-09-12-14-p...

vor 4 Jahrendiscuss

Do you have some numbers to back your "strong" doubts?

One widely cited source is the 'Lazard' report:

https://www.lazard.com/perspective/levelized-cost-of-energy-...

it puts onshore wind at between $26 and $50 per MW and the cost of offshore wind at an average of $83 per MW. I.e. the opposite of what you think.

Lazard could be wrong, and it would be interesting to hear why, backed by some numbers.

vor 6 Jahrendiscuss

Rurban wrote: "the very best (Formula 1) at 10 KHz".

how much of the above is a typo and how much is real?

I'm pretty sure 'KHz' is a typo which maybe should be kHz as in the start of the sentence. But even then, why are the very best running 50x slower than the trivial ones? Or did you mean MHz?

Do you have a link to an example of an F1 ECU with the clock rate specified?