Wikipedia:Reference desk/Archives/Computing/2011 May 6

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May 6

About music instrumens

Is it possible to interface two music instruments via usb like midi?. —Preceding unsigned comment added by 115.241.27.252 (talk) 03:26, 6 May 2011 (UTC)

You need to explain what you mean. Are you talking about electronic instruments like electric guitars and synthesizers ? You could certainly collect signals, convert them into MIDI format, and send them down a USB cable (or you could do it wirelessly). But why would you want to send that info to another instrument, rather than to speakers (or to a computer for storage and further processing) ? Are you asking about actually having an instrument play the MIDI file ? If so, that would require quite a change in the design of the instrument, much like a player piano required a major change in piano design. I don't see much point in doing that, as it would be cheaper and you'd get better sound to just play the MIDI file with normal speakers. StuRat (talk) 04:19, 6 May 2011 (UTC)

Be aware MIDI only sends note commands, it's up to the receiving instrument to make the sounds. You wouldn't send MIDI directly to speakers, but to a MIDI instrument or synthesizer that has speakers attached.

Be aware MIDI messages between instruments are note commands that take effect immediately. A MIDI file records these commands with time stamps. Instrument-to-instrument communication is usually with the immediate MIDI messages, not with the recorded MIDI files.

The main reason you would connect two MIDI instruments is because you like the controls on one and the sounds on the other. You connect them so you can use the first instrument's controls to control the second instrument's sounds. --Bavi H (talk) 16:54, 7 May 2011 (UTC)

Since this is the Computing Reference Desk, 115.241.27.252 may be thinking of electronic instruments, perhaps those that have both MIDI ports and a USB port, and already have the ability to send and receive MIDI commands. 115.241.27.252 may be asking if it's possible to connect two instruments for MIDI-like control using a USB cable instead of a MIDI cable. The main problem I can think of is that in a USB connection, one end is a host (type A connector) and the other end is a peripheral (type B connector). It might be unlikely that an instrument would have USB host capabilities. You would probably need to connect the two USB instruments to a computer. --Bavi H (talk) 16:54, 7 May 2011 (UTC)

What is the site that shows a comparison between the fair second hand price of items selling on Ebay?

It shows the fair second hand price and the percentage or amount that it differs from the current Ebay bid price... —Preceding unsigned comment added by 203.24.7.9 (talk) 09:42, 6 May 2011 (UTC)

There are that many different things bought and sold on ebay, I'd be surprised if a site like this existed, unless it was specialized to a specific category or item. The only thing I can suggest is to do a search of completed listings and see what the item you are after has been selling for. After all, a "fair" price is just what people are willing to pay for it.. Vespine (talk) 00:15, 9 May 2011 (UTC)

Bookmarking websites in Safari

Is it possible to bookmark websites in Safari and if so how? I am using Safari under Windows 7. Toshio Yamaguchi (talk) 12:32, 6 May 2011 (UTC)

A Google search turned up this General Rommel (talk) 00:38, 7 May 2011 (UTC)

If you just want it in the bookmarks bar, Just click the "+" button by the address bar, assuming you haven't removed it. Also, you can drag the website's favicon to the bookmarks bar. If you want to organize though, go to General Rommel's link. --Thekmc (Leave me a message) 01:11, 7 May 2011 (UTC)

Image thumbnails from wikipedia, archived?

Is there anywhere where one can download all wikipedia images as a dump. In the same way as the articles?, I can't be the only one on this planet that has thought of this. And 3.6 million pages with say 2-3 images each is quite a lot.. Electron9 (talk) 13:26, 6 May 2011 (UTC)

This functionality was disabled in 2007, so it appears you may be out of luck, unless you find a Wikipedia mirror that does allow this. That page does mention a utility that may be of use; and it mentions that scraping Wikipedia pages would work, though it's better for Wikipedia if you download databases rather than scrape the pages. Comet Tuttle (talk) 18:45, 7 May 2011 (UTC)

If no database is available well.. Electron9 (talk) 09:43, 10 May 2011 (UTC)

Virtual machines for web surfing.

Would using virtual machines when I surf the internet make my computer more secure. Specifically keeping one virtual machine for banking and one for casual surfing.

I am using VirtualBox to manage the virtual machines and are running ubuntu guests on a Windows 7 host. 88.90.43.140 (talk) 13:45, 6 May 2011 (UTC)

Yes... but only up to a point. Presumably much of the bad software that could compromise your personal information on the host OS would also be able to give someone the power to access your virtual machines. Now if you encrypted the virtual machines with additional protection, that would go much farther. I saner approach, IMO, would be to use Linux for your host OS, and virtual machines for the rare Windows software you somehow can't live without and cannot run via Wine. ¦ Reisio (talk) 14:15, 6 May 2011 (UTC)

I'm guessing the OP is more worried about the guest OSes been compromised via the web then the host OS, whether or not it's a sane approach Nil Einne (talk) 16:03, 6 May 2011 (UTC)

One of the more important uses of the PC will be gaming. So linux host is more or less out. Actually I aminterested in likelyhood of the host getting compromised via from things done in the guest. I more or less take it as a given that the guest will be compromised if the host is. Taemyr (talk) 16:22, 6 May 2011 (UTC)

A virtual machine is no more secure than a real machine is; it's how you use it that matters. If you get a virus on your virtual machine it can still become part of a botnet, compromise your banking details, etc etc. I personally sometimes use a virtual machine for testing downloaded programs I am unsure of, so that if they do turn out to be a virus I can simply delete the virtual machine and reinstall. I wouldn't want to do daily tasks on a virtual machine as they're much slower than real hardware. 82.43.89.63 (talk) 16:13, 6 May 2011 (UTC)

Shouldn't be "much" slower with relatively modern hardware. ¦ Reisio (talk) 18:03, 6 May 2011 (UTC)

Depends on your CPU. Most VMs can't use multiple cores, so if you have programs which multithread, and have multiple cores, VMs will be much slower. --Phil Holmes (talk) 14:57, 8 May 2011 (UTC)

Yes of course. But if I get malware on my virtual machine I can just delete the whole thing and start over, nothing I need to keep there is of interest. Taemyr (talk) 16:22, 6 May 2011 (UTC)

The guest and the host machine are just 2 different systems running on the same hardware, and malware infecting the former will not reach the latter if they are not connected to each other in some way. For example, if you use shared directories, or if you link them through a host-only network. (I use VirtalBox too.) Otherwise, the host will be secure. Think as if you had 2 different PCs connected to the same modem. Sorry for my English --151.56.113.184 (talk) 17:07, 7 May 2011 (UTC)

How do LaTeX package makers do it?

Do they have to create vector graphics of every glyph or symbol in their package for every possible permutation in which their symbols come together? Sooner or later the high level stuff like \frac{x^2_i}{\sqrt{2}} has to get translated down to raw pixels, and if I'm creating a package with a totally new squiggle that changes whether it's placed next to a character or a whole expression...how do they do it? 20.137.18.50 (talk) 14:42, 6 May 2011 (UTC)

Just as with any programming language, you start with some very simple functions and use those to make more complicated functions. Then, you can use those to make even more complicated functions. Eventually, you can do very complicated things with a single function call. You don't HAVE to use the single function call. You can type out all of the complicated code yourself. As for doing it yourself - you can write your own functions. It isn't common that you would need to do so, but many people do write their own. -- kainaw™ 15:07, 6 May 2011 (UTC)

Right. If you wanted to use a new type of squiggle in LaTeX, you would have to create a new font containing it. The font file contains the instructions for rendering the symbols at the pixel level. To get context-dependent rendering, you would have to write some fancy code in the LaTeX or TeX languages. Looie496 (talk) 16:46, 6 May 2011 (UTC)

Depending on the way you plan to use your "custom squiggle", and how often you intend to use it, it may be easier to create a SVG, PNG, or encapsulated postscript vector or raster image, and have your TeX environment include it as an image. When I was working with TeX, this was our standard procedure for all our non-equation "graphics," where the term "graphic" can be loosely interpreted to also include certain unusual equations, program outputs, and images. This allowed us to write custom rendering routines in the language and methodology of our own choosing; and then communicate the results to the TeX environment as a vector-graphic image for inclusion in the final paper. Nimur (talk) 17:01, 6 May 2011 (UTC)