Wikipedia:Reference desk/Archives/Computing/2011 August 11

= August 11 =

Does lowering the volume on an MP3 player increase battery life?
If the volume is at 50% then does that mean that 50% of the voltage is going to the headphones and the other 50% is being wasted as heat in the resistors (or potentiometer) that reduce the voltage, making it use the same amount of electricity as if the volume was at 100%? --Codell (talk) 01:35, 11 August 2011 (UTC)


 * Yes. If you mute the sound, your MP3 player will consume a little little power for display and (maybe) internal data processing. Marthelati (talk) 04:29, 11 August 2011 (UTC)


 * It's not a direct answer to the question, but the actual decoding of the MP3 format is fairly CPU-intensive (and therefore battery-intensive). Fifteen years ago, your average desktop computer was too slow to decode MP3 in real-time, the way your portable player can do with ease now. This processing certainly consumes a lot of power, even at 0% volume.  (talk) 07:17, 11 August 2011 (UTC)


 * You are misunderstanding how a resistor works. Take a good look at Ohm's law. The resistor does not "burn off" the excess - it reduces the total current flow. Increasing the resistance of the potentiometer (turning down the volume) decreases the current flowing through it and subsequently through the audio amplifier and speakers. It is analogous to a half opened tap/faucet - the rate of water flow through it is less than when it is fully open. As other answers have pointed out the audio amplifier and speakers may however only be responsible for a small proportion of the total power consumption of the device. Roger (talk) 07:40, 11 August 2011 (UTC)


 * I'm not familiar with the circuit design of MP3 players, but I would have expected that most of them control the volume electronically, rather than with a potentiometer, so very little energy will be "burnt off" in resistors. A volume control built into the headphones is more likely to be a potentiometer with greater energy loss, but not the 50% you calculate.  Remember that perceived volume is logarithmic (see decibel).   A significant proportion of the energy from the battery goes towards producing amplified sound, especially at high volume, so the answer is yes, battery life is significantly increased when you turn down the volume, but not doubled if you reduce the volume by 50%.  The exact percentage increase would depend on the particular model, and would require experimental data to determine because there are other factors such as battery capacity depending on current.    D b f i r s   08:41, 11 August 2011 (UTC)


 * I just want to add a link to an open source mp3 player implementation (started over 10 years ago) - a FPGA, likely specialized for the specific implementation to play MP3 files from some memory: http://www.pjrc.com/mp3/info.html, which in turn have little overhead compared to a standard PC 10 years ago Azalin (talk) 19:47, 16 August 2011 (UTC)

What? A METAL DETECTOR APP? (Android Marketplace)
Someone on a KurzweilAI forum said he had a metal detector app once, though he was sure it was a joke app.

I would believe that it was indeed a joke app.

On the other hand, what kinds of tech advances would be required of cellphone tech in order to create a real-working metal-detecting app??? --70.179.163.168 (talk) 05:39, 11 August 2011 (UTC)


 * Typical metal detectors work (roughly) by detecting interference in an antenna caused by the presence of metal. There's a bit more to it than that, but since cell phones do have antennas and can detect signal strength at least, it's not so difficult for me to believe that somebody might have been clever enough to write an app that interprets fluctuating signal strengths in such a way that it can act as a crude metal detector. Now, I don't know whether apps have that kind of access to the hardware, and I don't know whether patterns of changes of cellular signal strength are enough to actually make it work, so it very well could have been a joke. —Bkell (talk) 07:29, 11 August 2011 (UTC)


 * Many modern screenphones contain magnetometers, which they use to sense the strength and orientation of the Earth's magnetic field. This provides a basic compass function when the GPS and cell-based positioning systems aren't available. Data from the magenetometers is retrieved using the Android SensorManager and GeomagneticField APIs. I have a sensor monitoring app called GPS Status which shows a lot of the interesting information available to apps (GPS satellite constellation visibility, battery level, ambient brightness, pitch/roll/acceleration, and magnetometer data).  If I put the phone on a wooden desk, or hold it in space, it reports a magnetic field of about 46 μTesla. Placed atop a steel filing cabinet it reports 193 μTesla, an effect that's noticeable out to at least 10cm.  But it's hopeless at "detecting" anything smaller - any influence my watch or keys might have is less than the ordinary variation its sensor sees, even if held right under the phone.  So strictly speaking it can detect very large steel objects that are very close to it, so it's nominally a metal detector, but (I expect because it's relying on the Earth's magnetic field, rather than generating its own and observing the changes in what it receives back) its so insensitive that it's useful only for novelty value. -- Finlay McWalter ☻ Talk 09:03, 11 August 2011 (UTC)

Android device with a USB Host port
Are there any Android devices currently on the market or "comming soon" that have a USB Host facility built in? So far all the devices I have seen (various phones and a Samsung Galaxy Tab) do not have a type A (or Micro-A) USB port and so are limited to only be a peripheral instead of controlling other peripheral devices. Roger (talk) 08:31, 11 August 2011 (UTC)
 * In the coming soon category (very soon according to most sources - a matter of days to weeks rather than months) there is the Lenovo Thinkpad Tablet, don't be put off by the fact that it looks like a netbook on the website - that's the optional keyboard dock. Equisetum (talk &#124; email &#124; contributions) 09:53, 11 August 2011 (UTC)
 * I know someone with a fairly cheap Android tablet (I think a Zenithink ZT 180 rebrand). It has an ordinary type A port and I presume has USB host facility because it can support memory sticks (I think) and definitely can support USB mice (keyboard too although can't remember if I tested that) and from memory of results during my searches some 3G and wifi dongles as well. However bear in mind unless you have good programming experience or there is a good modding community you may still be limited by whatever drivers available on the specific Android distro provided by whoever made your tablet (and whether the software allows access to the periheral supported by those drivers when rooted or whatever). E.g. for this friend's tablet USB bluetooth adapters don't seem to be supported from testing and searches this seems to be a common problem. Nil Einne (talk) 13:11, 11 August 2011 (UTC)
 * BTW, the Samsung Galaxy Tab 10.1 apparently doesn't have a USB A port, but it either has USB host functionality built in (requiring only a passive adapter) or has some other connectivity function that enables a stand alone USB host device (my guess is it's the former) sinc according to our article: "A USB host adapter was made available in June 2011. The dongle plugs into the 30-pin dock connector and allows USB compatible accessories such as keyboards, mice, and thumb drives, to be connected to the tablet." Nil Einne (talk) 12:14, 13 August 2011 (UTC)

Cheapo Android tablet battery life
I've just bought a no-name "seven inch" Android minitablet that's described as having "Rockchip 2818 1.0Ghz (ARM+DSP+GPU)", 256MB and (?) 4GB of memory (I mean, aside from and Micro-SD card), and Android 2.1. It was new, and cost very little over the interwebs. I wasn't expecting much, but I was expecting a battery life longer than fifteen minutes, which is all I get when doing something innocuous like attempting to view a PDF. ("Attempting", because zoom as I wish, it's too small. I assume that some other software will do the job.) Fifteen minutes is of course so short that the device is worthless. I'm now drafting a chilly message to the dealer, but I'm wondering what to say. It's obvious to me that anything like this should be usable for four hours, and that it's just this example that's a lemon, and I should ask for a replacement -- but I'm an Android ignoramus and maybe it's common knowledge that the charge capacity of batteries designed for these particular devices halves every three months after manufacture; maybe I should ask for a different model. What battery life can one reasonably demand of a new (but slightly old-stock) cheapo cheapo tablet? (The minuscule user's guide for this one talks of a charging time of five hours [ha ha] but says nothing about how much use you can then get out of it.) -- Hoary (talk) 09:19, 11 August 2011 (UTC)


 * The screen is what mostly determines the battery life - based on the batteries you have. Some batteries have longer life. Some have shorter life. The best you can do is get better batteries and dim the display on the screen. (Note: The following is heavily influenced by the excessive frequency of which coworkers bring me crap they've purchased on shopping networks and expect me to make it work as well as an iPad...) Basically, you feel it should be illegal to sell electronic devices with terrible battery life. Similarly, it should be illegal to sell diet drugs that don't work. It should be illegal to sell credit consolidation plans that don't work. It should be illegal to sell mosquito repellent bracelets that don't work. The key concept here is caveat emptor. There will always be some ass who slaps together some garbage and tries to sell it. If you go after the no-name super-cheap garbage, you will most likely get garbage that comes from a no-name company that doesn't care about you and, even though it was super-cheap, you will be out the money you spent. -- k a i n a w &trade; 12:59, 11 August 2011 (UTC)


 * Ah, screen brightness. Well, I can reduce that when I get my paws on the replacement. I'd assumed, perhaps naively, that low-power screen technology would have improved (or that better options would have got cheaper) during the popularity of netbooks: at a given brightness level, this screen might consume even 100% more juice than it should, but surely not 300% more.


 * One way in which this toy resembles the iPad is that both hide the battery. I've no idea of where it is or what size it is.


 * I don't know about your part of the world, but in mine the options are expensive iPad (of course from a company that has a huge ad budget), expensive Android devices from companies that have big ad budgets, and cheap Android devices from companies I've never heard of. I don't begrudge Apple its profits, and I've bought from Apple in the past. But I'll get something that will "satisfice" me until swish tablets with repeatedly tweaked OSes cost less than netbooks. -- Hoary (talk) 14:08, 11 August 2011 (UTC)


 * I didn't say this earlier since it was mostly OT. But actually in New Zealand where I believe the OP is from, the Consumer Guarantees Act requires goods are fit for their normal purpose . Because of limited resources and other factors, this and other requirements often aren't particularly well enforced in the computing field or particularly against low end retailers and unlike is sometimes done in Europe, there's usually little guidance on what it actually means. But unless the device was sold as basically requiring a permanent power connection with the battery only for brief emergencies, and presuming the OP isn't doing something wrong I have strong doubts a tablet with only a 15 minute battery life would qualify. I don't know if there have been any legal cases and I don't know if I'd go as far as the OPs 4 hours, but I would expect at least 1 hour. I strongly expect organisations like the Consumers' Institute of New Zealand or TV shows like Fair Go would agree with me and writing to them is sometimes a useful step. The Citizens Advice Bureau  could perhaps often some guidance whether there's ever been any cases. Ultimately taking a case before the Disputes Tribunal . I'm presuming of course the OP has purchased the item from a retailer or something of that sort, not via an auction like TradeMe or even from overseas in which case they've elected (knowingly or not) to purchase something in a manner not covered by the extensive consumer protections of NZ law. Nil Einne (talk) 16:06, 11 August 2011 (UTC)


 * It very probably has a broken battery. Check with the manufacturer. Dmcq (talk) 18:48, 11 August 2011 (UTC)

Unable to create an Yahoo account.
I cannot create an Yahoo account, it said I answered the CAPTCHA incorrectly but it was correct. Windows 7 with Internet Explorer 9, help. Marthelati (talk) 13:16, 11 August 2011 (UTC)


 * How many times did you try? Nil Einne (talk) 13:19, 11 August 2011 (UTC)

Indefinitely many times. Marthelati (talk) 13:24, 11 August 2011 (UTC)


 * Did you check carefully that your upper and lower case characters were correct? Did you try loading a different captcha code? Did you try using the audio code instead? Are you sure that it was the the captcha code that was wrong, and not that you were missing some other piece of required information? Did you try reloading the page and trying again? These are generally pretty obvious, but I'm just putting them out there, cos there's not really much reason it shouldn't work. --jjron (talk) 15:28, 11 August 2011 (UTC)


 * The OP claims they tried 'Indefinitely many times' which I presume means they tried many different captchas. I do agree an audio captcha may be useful. Nil Einne (talk) 16:13, 11 August 2011 (UTC)


 * Is "an Yahoo" British English, or just plain wrong, like the use of "indefinitely" in place of "definitely" ? StuRat (talk) 17:31, 11 August 2011 (UTC)


 * My guess is English not first language or at least pretending to be. User has been blocked as an abusive sockpuppet so hopefully we'll never know Nil Einne (talk) 18:07, 11 August 2011 (UTC)

JDK, JRE, x86, x64
What I already know:  JDK contains the JRE. There's no need to install the JRE after installing JDK. 32-bit version of JDK works well on 64-bit OS. Some well written programs check if other instance exists and refuses to install if there is any. 

But I don't know:  Does JDK x64 contain the JRE x86 and vice-versa? What is the purpose of 64-bit JDK, when I am writing a program for a virtual machine? I already have JRE installed. Now I installed JDK. Can JDK detect and not overwrite it? I know it depends on those who develop JDK, but does anyone know? 

The Oracle website does not have any explaination at all (or because I haven't found it yet). -- Livy the pixie (talk) 14:16, 11 August 2011 (UTC)


 * What is the purpose of 64-bit JDK, when I am writing a program for a virtual machine? The compiler, virtual machine, etc are 64-bit native-code applications (not Java; written in C or C++), and hence can use the extra facilities of the 64-bit chip (it might even compile more quickly). The java byte code should be identical. --Colapeninsula (talk) 14:35, 11 August 2011 (UTC)


 * suggests the compiler is written in Java although I presume as you said, it's usually distributed compiled to native machine code rather then Java byte code. In answer to the OP, I'm pretty sure the Windows x64 JDK as with the JRE doesn't come with the x32 JRE. You need to download and install that seperately if it's desired. Nil Einne (talk) 18:16, 11 August 2011 (UTC)

Linux Keyring prompt fix
According to this and this website, the issue i currently am having with a wireless network keyring can be resolved by deleting a default keyring file in a certain location. However, this file does not exist on my system.

From terminal:

home@home-HP-Pavilion-dv9000-EZ458UA-ABA:~/.gnome2/keyrings$ ls    login.keyring  user.keystore.AZNLQV  user.keystore.Q84TQV user.keystore user.keystore.HD0RQV  user.keystore.WU8TQV

home@home-HP-Pavilion-dv9000-EZ458UA-ABA:~/.gnome2/keyrings$ ls -a .  login.keyring  user.keystore.AZNLQV  user.keystore.Q84TQV .. user.keystore  user.keystore.HD0RQV  user.keystore.WU8TQV

My guess is maybe i have a different version of the software? though that is rather more a stab in the dark than an educated guess. Should i delete one of these files which may operate the same as the intended default.keyring?

216.173.144.164 (talk) 14:48, 11 August 2011 (UTC)


 * It's hard to answer questions like this without knowing what Linux distro you are using. Looie496 (talk) 20:07, 11 August 2011 (UTC)

What computer manufacturer gives better warranty deals?
I believe I should move on from Dell with my next laptop/swivel tablet because some of their warranty deals are rip-offs.

I was promised year-long software warranty tech support for $239, then I learned that $239 covers just 4 incidents, then I was offered $110 for another 3.

I want warranty packages that are good for a period of time, period. Not for a period of time in a number of incidents.

So what competing PC manufacturer will offer better warranty packages (to include software warranties, not just hardware) than Dell?

(Also, this manufacturer has to allow me to choose my own parts/components like how Dell & Apple does when I shop for a new system on their websites. That would help me a lot. Thanks.) --70.179.163.168 (talk) 18:01, 11 August 2011 (UTC)

Why would a toolbar disappear?
I could have just changed computers at this library, but when I asked someone for help she asked if there was a mouse, and when I moved my mouse across the top of the screen the toolbar magically appeared. Then it disappeared. I should add that on Wikipedia, the sign-in link disappears if the toolbar is there, as do "My contributions".

Most of these computers are Internet Explorer, and another one said it was Windows XP. I don't know what this one is. Vchimpanzee ·  talk  ·  contributions  · 18:45, 11 August 2011 (UTC)
 * Don't take this personally, but I work in IT support and i'm really struggling to understand what you mean. I could have just changed computers at this library, don't understand what you mean by this. toolbar magically appeared. what do you mean by "toolbar"? What did it look like? Did it have menus or buttons and what did they say? "internet explorer" is not a kind of computer, it's just a program you use to browse the internet, it is the default browser installed on windows computers.


 * If I had to take a wild guess, maybe someone has dragged the task bar to the top of the screen and selected the "auto hide the task bar option"? Click this task bar image, does it sort of look like that? If it is, you can right click it, select "options" and un-tick the box that says "auto hide the task bar". If you are feeling adventurous, you can also try to drag it back down to the bottom of the screen. You have to make sure "lock the task bar" is NOT selected when you right click the task bar, then you have to click and hold on an empty part of the task bar and literally drag it down to the bottom of the screen and then let go of the mouse button. If it's NOT that, then I wrote all that for nothing lol.. Vespine (talk) 22:59, 11 August 2011 (UTC)


 * If I had to take a wild guess, press f11.--Shantavira|feed me 07:29, 12 August 2011 (UTC)
 * You know, I looked all over the web and all over Wikipedia for the correct terminology (as well as a possible solution). When I say Toolbar, I mean there was no back button, no forward button, no place to type the URL. If I move the mouse across the top of the screen in just the right way, which sometimes is more difficult than it is at other times, because sometimes nothing happens, then all that stuff appears.


 * I'm no longer at that library but they need to fix it. And if I say a computer is "Internet Explorer" then you're supposed to know what that means. I don't think anyone understands how hard it is just to think how to explain a problem, much less do it in the exact way you want.


 * I looked up F11 and I guess that is the problem. Vchimpanzee ·  talk  ·  contributions  · 17:54, 12 August 2011 (UTC)

Networked printer problems
In the office I work we have 4 PC's connected to a networked printer all through a server, but every now and again one of the PC's won't print and what we have to do is go into Devices and Printers and un-install the printer and then re install it. Has anyone any ideas why this is happening as it has happened on the 3 PC's that are connected wirelessly but not the one that is directly connected to the printer by a cable, thanks. Mo ainm ~Talk  21:37, 11 August 2011 (UTC)

Using VLC to add video effects/adjustments to vids
I use VLC on Ubuntu. You can easily add video effects and adjustments to videos (like changing the contrast, or rotating the vid) during playback but can you make those changes permanent? The Convert/Save menu doesn't seem to be able to do that, as far as I can tell (it's not the easiest thing in the world to use). TresÁrboles (talk) 21:47, 11 August 2011 (UTC)


 * I'd use  or , but you might prefer using a GUI app, such as… (in no particular order) LiVES, CinePaint, Avidemux, Kino, CineFX, Kdenlive, PiTiVi, Cinelerra. ¦ Reisio (talk) 11:02, 12 August 2011 (UTC)

Tr0ub4dor&3 vs. correcthorsebatterystaple
Just some fact-checking. (that's from xkcd.com) Does the first password has 2^28 of entropy and the second 2^44? Is the second password harder for a computer to crack?Quest09 (talk) 23:46, 11 August 2011 (UTC)


 * For future reference, the relevant comic is #936. In practice the answer depends on the sizes of the dictionaries from which the two passwords (or their components) are drawn. -- Finlay McWalter ☻ Talk 00:02, 12 August 2011 (UTC)


 * And here's some discussion from Randall Munroe the cartoonist, of the bases on which he drew this particular cartoon. --Tagishsimon (talk) 00:06, 12 August 2011 (UTC)


 * Also of possible interest is the PGP passphrase faq, which advocated a similar strategy 18 years ago (see the answer to the first question). 130.76.64.116 (talk) 00:14, 12 August 2011 (UTC)


 * In the latter case it looks like he's using 4 dictionary words, so that's 44/4 == 11 bits each. That assumes a dictionary of 2^11 entries, which is 2048, which seems rather small. -- Finlay McWalter ☻ Talk 00:12, 12 August 2011 (UTC)
 * The author proceeds to only count certain bits: he assumes that the only relevant entropy is defined by the decision-tree as a passcode string is created per a specific recipe. For example, he counts the bit-length of a lookup-dictionary of known words.  This is simply wrong.  This methodology quantifies representations of abstract pieces of information with "bits" according to a known recipe for generating password sub-strings; but it then presumes that the attacker knows the recipe; and the author fails to account for any bits of entropy related to the fore-knowledge of the recipe.  (Specific example: which words are in the lookup-dictionary?  How long is the dictionary?  Those pieces of information have entropy too!)  If the method had any merit, it was lost at that point.  I would tag this whole comic with ; the assumptions and conclusions may be suitable for a comic strip, but are probably not up to snuff for a cryptography or security-best-practices publication.  Kudos to the author for bringing attention to the concept of heuristic-based password guessing, rather than pure brute-force iteration; but his math is off by a few orders of magnitude.  Nimur (talk) 00:46, 12 August 2011 (UTC)
 * I think that it's correct to discount those bits; after all, a recipe is good precisely if it still works well when everyone uses it. Paul (Stansifer) 02:13, 12 August 2011 (UTC)
 * The latest (episode 313) Security Now podcast discussed this comic pretty well: . They talk about it pretty early on in the podcast. - Akamad (talk) 01:58, 12 August 2011 (UTC)
 * The discussion of the comic starts at about 19:20 and ends at about 32:00, but I don't recommend it. Steve Gibson is one of those celebrity "experts" whose main skill is self-promotion. I'd even go so far as to call him a crackpot, based on his web site. Munroe clearly understands what constitutes a strong password; Gibson is clearly very confused. -- BenRG (talk) 10:40, 13 August 2011 (UTC)
 * Gibson does not claim that his little tool is a password strength meter. He just presents some metrics for understanding how many passwords can be created by combining a certain set of elements. 88.14.196.229 (talk) 13:53, 13 August 2011 (UTC)