Dan's Data letters #137
Publication date: 31-Dec-2004.Last modified 03-Dec-2011.
Hacking hosts
I read your letters column, and followed the link to the list of sites to block. While it sure looks comprehensive, how do you tell Firefox or IE to not talk to those sites? There is a spot in FF to tell it to not load images from specific places, but you enter addresses one at a time there. Same with IE's restricted sites dialog. Is there a way to import those wholesale?
Mike
Answer:
It's a hosts file; it's what your computer uses to look up IP addresses from hostnames before asking your ISP to do
it. If you put an entry in the hosts file that directs requests for example.com to 127.0.0.1 (or some other
loopback address), no software on your computer will
be able to see the real example.com - no browsers, no mail clients, no nothing.
Anything that already knows what example.com's IP address is and looks at that directly will still be able to see it just fine, so this isn't a foolproof way of denying all software access to particular servers. And it'd be perfectly possible for some piece of malware to just empty the hosts file, or selectively remove entries for anything it liked, provided it was running from an account with adequate permissions (which it probably would be, since the overwhelming majority of Windows users use an administrator account all the time). But for blocking ads and less devious spyware-type apps, simple host file entries do the trick, and are very easy to set up and remove.
There's more info about this on one of the pages I linked to.
From the makers of Tin Can Telephone
I recently bought a new "Insignia" P4 PC (from Best Buy). In the front of the computer tower it has slots called..."Memory Stick", "SmartMedia", "CompactFlash/Microdrive", and "SD/MultiMediaCard". This is all new to me. My last computer I bought was about 6 years ago. My new computer is a very big bump up from what I had before.
I've found ads for "3-in-1 Digital Cameras" that sell for about $US30. Are they a dud or a deal, and are they usable with my WinXP computer?
Angel
Answer:
The memory card slots in the front of your PC will let you read and write the cards used in digital cameras, palmtop
computers, and some MP3 players.
Regarding the camera: Never buy a digital camera from someone who won't even tell you what the resolution is.
This camera is the same kind that Aiptek used to sell as the Pen Cam. It'll probably work OK with your XP machine, but as you'd expect, it's basically just a toy. You can take some surprisingly good pictures with these super-cheap baby-cams, but you can also take surprisingly good pictures with a film camera made out of paper. That doesn't mean there's no point in buying a proper camera.
If you want a good general purpose happy-snap-quality digital camera with all of the features of a proper digicam - enough resolution for great looking A4-size prints, zoom lens, autofocus, screen on the back, memory card image storage - you'll have to resign yourself to paying quite a lot more than you will for a toy-cam, but it really is worth the extra money. And you won't actually necessarily have to pay that much more. Nikon's Coolpix 2100, for instance, is a brilliant little entry-level camera, and it's selling for less than $US150 these days. It comes with a pokey little 8Mb memory card, but CompactFlash cards to suit it are cheap; a 64Mb or 128Mb card will probably be ample. And it runs on plain AA batteries.
The Coolpix 3100 has better specs than the 2100 and doesn't cost very much more. Canon's PowerShot A75 is a bit more expensive again, but still comes in at only about $US200 including its standard, almost-big-enough-for-casual-shooters 32Mb memory card.
The 1/2 scale Enterprise-A is next
I'm building a mock life-sized shuttlecraft in my backyard. I'm going to use a lot of LEDs inside for "emergency lighting", and also on the outside for effects. I'm running the whole thing off of 12 volt lead acid batteries and using solar panels to recharge them. This is also an experiment in renewable energy as much as anything for me. I want to get the best efficiency out of everything, so I am trying to avoid using resistors.
I am told that I always need a resister for an LED or series of LEDs. I have tried putting 6 LEDs in series and hooking them directly to the 12 volt system. These LEDs are yellow, and run at 2.1 volts. Since my battery puts out about 13 volts, these LEDs are running at around 2.16 volts each. I've run them for weeks and they haven't burned out yet, but once I mount these things inside I'll never be able to replace them so I want to make sure I'm doing anything I can to keep them from going out. What would your suggestion be? I want to run hundreds of LEDs and I don't mind linking them in groups of 6 or however many I need in series. I don't want to waste energy in resistors, but I also want them to work for a long, long time.
David
Answer:
Although LEDs have a rated voltage and current, the actual voltage drop across them (which you can also think of as
their resistance at a given point in time) varies. The hotter they get, the lower the voltage across them will be,
and the more current will flow, and the hotter they'll get, et cetera, until death. A series resistor can prevent
this "thermal runaway" process from happening.
If, however, the power supply just plain doesn't output enough volts for thermal runaway to get started, then you don't need a series resistor. When your batteries are tippy-top charged they may output a bit more than 13.8 volts, but as you say they won't normally be that high, and even 13.8 across six series LEDs probably won't be a big deal.
If you end up overdriving the LEDs for a significant amount of time, though, they may get dim a very long time before the "hundred thousand hours" the manufacturers always promise. This is a particular concern for LEDs that're glued in place or otherwise kept away from air flow, which'd otherwise help them keep cool. So I recommend that for safety's sake you do use however much series resistance you need to keep the LED current draw down a bit below their rated current (probably 20mA). If you keep the current through each LED to, say, 15mA, they won't be very much dimmer, but will be guaranteed to last a very long time without dimming.
In a situation like this, just fudging around with alligator clip leads, a mixed bag of resistors and a multimeter is a good enough way to find the right resistor value. You're probably talking around the 100 ohm mark for six of the LEDs you mention from a nominal 13.8 volts. In this situation, the amount of power wasted in the resistor will be tiny - around 30 milliwatts.
A noble quest
I'm looking for a chunk of tungsten. I can't justify spending much money on something so useless, and I've been unable to find something satisfactory. EBay sometimes has a few pieces that are too small or too expensive. I've browsed industrial supplier's websites for hours (lusting particularly after the tungsten spheres these folks make - do you realize a 4" sphere would weigh something like 10 kilos?!), but I'm certain they would be entirely out of my price/quantity-desired range.
With your undoubtedly vast network of admiring contacts, I thought you might have some clever idea where I might be able to pick up a coupla pounds on the cheap.
Erik
Answer:
Sorry, no idea. Fortunately, people send me PayPal donations, which I use as my slush fund
for buying stuff I don't need on eBay.
My Tiny Expensive Paperweight Of Doom is in the mail to me at the moment.
I spent a while, as you have, looking for cheap options, but didn't find any for lumps that're more than trivially small - and tungsten is, of course, not like lead; you can't just collect a bunch of little lumps and melt them into a big chunk on your stove.
All I can suggest is that you look for odd things like those on Theodore Gray's (the above eBay listing is from RGBco, whose element collections are a T. Gray co-production) tungsten page.
Surplus military components or projectile pieces, goofy golf club inserts, stealing Oliver Sacks' wallet...
Looks like a duck, walks like a duck...
In a past letters column you said:
"Since, as far as I know, Mannatech have never presented credible evidence to the contrary, I don't think there's any reason to believe "Ambrotose" doesn't contain anything that your body can't make for itself, or get from a normal diet."
First of all, you haven't done your homework before making a public statement.
Second, Mannatech has presented credible evidence and has a whole Web site full of third party validation.
Third of all, quacks like you hurt my independent business by misleading the public.
Fourth, I'm reporting your use of a patented trade mark name to Mannatech's legal department.
Ken
Answer:
Actually, Ken, I have done my homework. I even know what a "quack" is - it's
a medical charlatan. I don't profess
to be any kind of medical practitioner, unlike, arguably, people like you who promote
multi-level marketed products that're supposed to treat
or prevent disease, so I can't be a quack.
Anyway.
Dig through Mannatech's claims and you'll find studies in real medical journals that say all sorts of things about how important various sugars are in human metabolism, cellular activity, et cetera. This is unquestioned. You will not, however, find any repeatable studies not done by Mannatech themselves that demonstrate that eating their special expensive supplements will do anything to the levels of those sugars in your body, or to your health, that eating a healthy diet of normal food (or, indeed, candy and potato chips...) will not.
There are many "supplements" that have this problem - they include some substance that's important to the body, but when you eat them you just digest the substance like anything else. Your body creates the substance all by itself, from the basic building blocks supplied by digestion and respiration. The body can't absorb the substance directly from the stomach or gut.
It is my opinion that Mannatech's promotion of their expensive supplements as being of use in the treatment of various serious diseases is reprehensible. I think they practice health fraud. If you believe their products work, as I presume you do, then I do not think you are practicing health fraud by selling them; fraud is lying for gain, and you're not lying if you honestly believe you're telling the truth.
You may, however, still be open to prosecution (or at least condemnation) because of your failure to make adequately diligent inquiries into the legitimacy of the products you're selling.
Oh, and let me know how you get on with that "patented trade mark" thing.
Nike! McDonald's! General Motors! Nyaah!
(Ken went on to send me a study that showed that sugars are important in cellular activity, and went on to say that he'd seen the evidence in his own health and that of his friends, so there.)
Next up: Do different coloured socks affect the sound?
I found this the other day. It's a long and detailed article on a topic dear to your heart. In summary:
"Using the blind ABX protocol, we failed to hear any differences between an assortment of generic power cords and Nordost Valhalla. Therefore, we cannot conclude that different power cords produce a difference using the blind ABX protocol. However, we also cannot conclude that there are no differences. We simply failed to prove that differences can be detected to a statistically significant degree using a blind ABX protocol."
Lachlan
Answer:
"...so, all you people who think science is engaged in an active campaign to suppress fine music reproduction, please
don't cancel your subscriptions."
A wishy-washy statement like that is about all that I expect from a hi-fi magazine that doesn't want to honk off its anti-science readers, but I was pleased by the much more definite Editor's Note on the end of the piece.
By the way, the possible explanation for the failure of the subjects to detect a difference - that swapping power cables takes long enough that people's auditory memory of what the last cable sounded like has faded before they hear the next one - would also invalidate all of the audiophile anecdotes about how much better their systems sounded when they swapped in their new whiz-bang lead. A listener swapping the lead on his own gear can only take even longer to do it, and be even more distracted, than a testee waiting for someone behind a curtain to swap a lead. And then, of course, there's the issue of "break-in", with audiophiles insisting that various cables take hours, days or weeks of use before they sound their best. Oy.
And it goes on
NEW from Spumco - from the makers of "Brick" and "Bin Liner" comes "Block Of Wood" (now with extra woodness).
Yes, "Block Of Wood" will revolutionise your listening pleasure through its patented "Cable Tie" technology - order one today while stocks last!
Hmmmm...
Andrew
Answer:
At least this product does not, itself, come with any thrilling claims about the spectacular difference its
kabbalistically
enhanced
cellular structure will make to the impact of your
chosen music upon your various chakras. It could; some out-there
audiophiles are convinced that different kinds of stand and shelf for solid-state components can make a difference to the sound, and
so sit their transistor amps on things like stone blocks. There's not a darn thing that's microphonic in a transistor
amp (as opposed to, say, turntables and tube amps), but nonetheless they swear that magnetically suspended platforms,
or whatever, enhance the fragrance and jocularity of the music.
The device this particular piece of wood is meant to support, mind you, is a great example of "mainstream audiophile nut" technology. Many audio-hardware-enthusiast types are convinced that "jitter" from typical, or even quite expensive, digital playback equipment is clearly and commonly audible, and so it's a good idea to buy a replacement high quality clock device - like the "Superclock" mentioned here - to reduce it. Or, indeed, to invest in some damn thing that's supposed to correct the alleged effects of different cables on jitter.
Given the folly of wasting any of the six to eight hundred thousand hours you'll probably have on this world on tedious and unproductive pursuits, it is, I think, entirely fair to immediately categorise any product that claims to give your music more "dimensionality" and less "grit" as nonsense. But jitter is, at the very least, actually a real technical phenomenon. This immediately puts it several orders of plausibility magnitude ahead of some of the things that audiophiles spend money to fix.
Heck, jitter's more plausible, even, than the things like "skin effect" that're also real but only apply to things definitely beyond human perception (in the case of skin effect, higher frequencies than humans without a big "S" on their chest can hear).
Jitter, however, does still seem to only be a real problem when you wander a reasonable distance away from the scientific method. I sure as heck ain't never heard it, but as the various people who've e-mailed me to tell me things like "everything Sennheiser make is garbage" would cheerfully tell you, I'm a cloth-eared git who can't tell Metallica from Morrissey.
Here and here is some more reading you didn't ask for.
And, finally...
Had a check of the site mentioned in the "Audiophile knobs" letter while bored at work and found this little gem.
"A new concept developed by Audio Consulting has left us speechless! We now feel up to 80% of sound is in the mains!"
John
Answer:
It leaves me speechless, too.
