|
|
This evening I tested some Noise Canceling Headphones (as described in my previous post [1]).
I first tried the ones on sale at Brookstone [2], they were the on the ear type so there was never a chance that I would buy them but they seemed like good ones to test. I wore them for about 10 minutes while I walked around the store looking at all the electronic stuff that’s on sale. I noticed that they were much more effective at filtering low frequencies and regular sounds. So for the Christmas music that was playing the music was mostly filtered just leaving the sound of the singing. Also I was able to talk to the guy who worked there and hear him clearly when the noise canceling was turned on – this can be considered a bug or a feature depending on your planned use. When I listened to electric fans the sound of the buffeting air was filtered just leaving the high pitched bearing noise.
It is well documented that there is a hissing sound from noise canceling headphones and sometimes a feeling of pressure. I didn’t hear any hissing but it did feel a little different when I turned on the noise canceling. After 10 minutes I didn’t feel in any way uncomfortable, so I could probably survive an entire flight while wearing such headphones. I can highly recommend the customer service at the Brookstone store in Menlo Park. The guy who was working there was totally helpful, even by US standards his customer service was really good. Sometimes when you make an unusual request (such was wanting to try the merchandise for an extended period of time) the staff aren’t particularly enthusiastic, but I had no problems at Brookstone!
After Brookstone I went to a Bose store and tried the Quiet Comfort 15 noise canceling headphones [3]. The Bose store conveniently had a device configured to emulate the sound of a jet engine to demonstrate how the QC15 stopped that. I was quite impressed with that. I did feel that the QC15 was a little light for my taste, I would rather have something bigger and heavier with thicker padding to improve the passive resistance to sound. But I expect that many people would like it to be small and light as it’s designed for travel.
I visited a Sony store a couple of times, but no-one seemed able to serve me. I’ll go there again some time when they are less busy.
Finally I have to note that I have received a significant number of comments suggesting ear-bud type devices. I suggest that anyone who doesn’t mind wearing such things should consider ear-bud type devices. But as I can’t stand such things I will continue my search for over-ear headphones. I may end up just buying the Bose QC15, they seem to be good enough and not really expensive.
My patience with the noise of airlines has run out, on my trip from AU to US I didn’t get any sleep due to the cramped seat and the noise of the plane. While I can’t do anything about the cramped seat without spending a lot of money it seems that I can do something about the noise with moderate expense.
I’ve been researching Noise Canceling Headphones [1]. The principle of such devices is that they have a microphone on the outside and a speaker on the inside to generate sound that is 180 degrees out of phase which will then almost cancel out the ambient noise. Apparently such devices are very effective for low frequencies but less effective for high frequencies. High frequencies are more easily blocked by sound insulation, so the ideal seems to be “around the ear” headphones with lots of padding to passively stop noise with active noise canceling to deal with the lower frequencies.
So I’m now planning on buying a set of headphones before I leave the US.
Choice Magazine (an Australian independent product review organisation) published a review of noise canceling headphones in 2007, it has some interesting information but is not suitable for buying advice today [2]. Choice gave the best results to the Jabra C820s which had just gone out of production when they published the review and by now could only be bought on eBay. The Jabra had an active cancellation of 14.3dB and a passive cancellation of 8.3dB. The best active cancellation of all the reviewed products was 19.5dB for the Bose QuietComfort 3 – which incidentally only had a passive cancellation of 4.8dB. Both the Bose and Jabra products got good reviews in a mailing list discussion. It’s a pity that Jabra is now only manufacturing products for call centers.
I am not considering the headphones that go on top of the ears, they will inherently give less passive protection due to the design and they will annoy me. I am also not considering the ear-buds because I don’t like putting things in my ears. I will note that there are some very positive reviews of some of the ear-bud devices. The Etymotic Research devices get very good reviews and are apparently on sale at reasonable prices in Apple stores (among other places) [3]. Anyone who wants noise-canceling headphones and disagrees with me about the desirability of ear-bud type devices should probably consider them.
The Bose QuietComfort 15 is selling for $300 (NB for this post all prices will be in US dollars) [4]. It has microphones both inside and outside the ear cup to allow better detection of ambient sound. A single AAA battery is supposed to last 35 hours, it has a detachable audio cable (for use in just blocking noise), and comes with an airline adapter (for the two-port airline sockets). It does require being turned on to listen to audio, some headphones allow you to turn off the noise canceling feature to listen to music without a battery – this doesn’t matter for my planned use. They have a volume switch (low and high settings) to cope with airlines that set the volume too high. They are specifically designed for passengers in commercial jet aircraft. Surprisingly the Bose web site doesn’t mention the number of dB of audio protection and none of the reviews I have read have mentioned it either.
The store Brookstone was recommended, they have some unbranded noise canceling headphones, but as they are on the ear and more expensive than comparable Sony products ($130 vs $100) I eliminated them quickly.
Sony has a good range of noise-canceling headphones [5]. They have ear-buds starting at $90 and on-ear headphones for as little as $50. They have two models of over the ear headphones that are advertised at $200 and $400. The MDR-NC60 costs $200 and reduces noise by 12dB at 200Hz while the MDR-NC500D costs $400 and reduces noise by 20dB at 160Hz. I don’t know why they didn’t measure both headphones at the same frequency or give any information on passive sound insulation. They state that the MDR-NC500D was voted as being better than the Bose QC2 and QC3 but made no such claim about the MDR-NC60 – presumably the older Bose devices were rated as better than the MDR-NC60, and I have to wonder about how the Bose QC15 would compare to the MDR-NC500D. The MDR-NC500D has an internal Lithium-Ion battery that lasts 16 hours and can take a pair of AA batteries as well for a total of 28 hours.
The Sennheiser PXC 350 claims up to 32dB of passive attenuation and up to 18dB of active noise compensation [6]. Their claims about NoiseGuard (TM) cause me to lack confidence in their products. The PXC 350 is advertised at $330 and the reviews that I have read suggest that the Bose might be a better product. Sennheiser also has PXC 450 which offers 23dB of active noise compensation and costs $450. I am not going to pay $450 for headphones.
It seems that the choice for over the ear noise canceling headphones comes down to the Sony MDR-NC60 at $200 and the Bose QuietComfort 15 at $300. I have the impression that the Bose product is better, but whether it is $100 better is the question. Also while I haven’t forgiven Sony for Rootkitting their customers [7], this is not going to prevent me from buying the headphones that best suit my needs.
Does anyone have any suggestions? Did I miss a good brand that I should be considering? Does Sennheiser have some redeeming features that I missed?
I’ve been investigating the Ext4 filesystem [1].
The main factor that is driving me to Ext4 at the moment is fsck times. I have some systems running Ext3 on large filesystems which I need to extend. In most cases Ext3 filesystems have large numbers of Inodes free because the relationship between the number of Inodes and the filesystem size is set when it is created, enlarging the filesystem increases the number of Inodes and apart from backup/format/restore there is no way of changing this. Some of the filesystems I manage can’t be converted because the backup/restore time would involve an unreasonable amount of downtime.
Page 11 of the OLS paper by Avantika Mathur et al [2] has a graph of the relationship between the number of Inodes and fsck time.
Ext4 also has a number of other features to improve performance, including changes to journaling and block allocation.
Now my most important systems are all virtualised. I am using Debian/Lenny and RHEL5 for the Dom0s. Red Hat might back-port Ext4 to the RHEL5 kernel, but there will probably never be a supported kernel for Debian/Lenny with Ext4 and Xen Dom0 support (there may never be a kernel for any Debian release with such support).
So this means that in a few months time I will be running some DomUs which have filesystems that can’t be mounted in the Dom0. This isn’t a problem when everything works well. But when things go wrong it’s really convenient to be able to amount a filesystem in the Dom0 to fix things, this option will disappear for some of my systems, so if virtual machine A has a problem then I will have to mount it’s filesystems with virtual machine B to fix it. Of course this is a strong incentive to use multiple block devices for the virtual machine so that a small root filesystem can be run with Ext3 and the rest can be Ext4.
At the moment only Debian/Unstable and Fedora have support for Ext4 so this isn’t a real issue. But Debian/Squeeze will release with Ext4 support and I expect that RHEL6 will also have it. When those releases happen I will be upgrading my virtual machines and will have these support issues.
It’s a pity that Red Hat never supported XFS, I could have solved some of these problems years ago if XFS was available.
Now for non-virtual machines one factor to consider is that the legacy version of GRUB doesn’t support Ext4, I discovered this after I used tune2fs to convert all filesystems on my EeePC to Ext4. I think I could have undone that tune2fs option but instead decided to upgrade to the new version of GRUB and copy the kernel and initramfs to a USB device in case it didn’t boot. It turns out that the new version of GRUB seems to work well for booting from Ext4.
One thing that is not explicitly mentioned in the howto is that the fsck pass needed to convert to Ext4 will not be done automatically by most distributions. So when I converted my EeePC I had to use sulogin to manually fsck the filesystems. This isn’t a problem with a laptop, but could be a problem with a co-located server system.
For the long term BTRFS may be a better option, I plan to test it on /home on my EeePC. But I will give Ext4 some more testing first. In any case the Ext3 filesystems on big servers are not going to go away in a hurry.
I’m about to leave for San Francisco, so my SE Linux Play Machine is turned off and will remain off until after I return.
Above is the picture of the RFID device in my new UK passport. The outer wire loop is 72mm * 42mm which is by far the largest RFID device I’ve seen. It appears that they want the passport to be RFID readable from distances that are significantly greater than those which are typically used for store security RFID devices. I couldn’t properly capture the text on the page which says “THIS PAGE IS RESERVED FOR OFFICIAL OBSERVATIONS, IF ANY“. The plastic layer that protects the RFID device leaves a 3mm margin that could potentially be used for official observations. Assuming that they don’t write in really small letters I guess this means that either they don’t make official observations on the passports nowadays or that any such observations are stored electronically where the subject has no good way of discovering them and objecting.
Above is a picture of the front cover of my passport which shows the RFID logo. Both images have links to the full resolution pictures.
On Sunday I leave for a two week business trip to San Francisco, this will be my first trip with my new passport. I’m thinking of taking some aluminium foil to wrap around my passport when it’s not being used. I don’t expect to really gain any benefit from doing so, it’s a matter of principle.
Cory Doctorow wrote an interesting little column for Make magazine about Wikipedia and the way that it “contains facts about facts” [1]. One of the issues with this is that you can’t (or at least shouldn’t) make corrections based on your own knowledge of a subject, you need to cite references. Cory gives a hypothetical example where a world renowned expert couldn’t simply fix an error in Wikipedia, but they could give an interview with the New York Times decrying the quality of Wikipedia and citing the correct data – then once the NYT article was published it could be referenced as an authoritative source and the page updated.
Mako wrote about the Wikireader (an offline reader for Wikipedia) and advocated a facility for writing changes while offline and uploading them [2]. From the perspective of improving the state of the art in computer science and making new features available for more users this sounds like a great idea. But in terms of fitting in with the way Wikipedia works it doesn’t seem viable to me.
Any time that you need to use an offline Wikipedia reader it seems that it will either be impossible or unreasonably difficult to gain the net access necessary to find the reference that Wikipedia requires. Sure you could fix spelling errors, reformat paragraphs, etc but not do anything serious. I wonder how many people actually put any serious effort into Wikipedia with the sole purpose of making it more readable. In terms of my own editing I have made a number of changes that improve readability, but all of them were due to reviewing pages for technical accuracy.
One of the comments on Mako’s post suggested that instead of having an option to directly edit pages there be an option to take notes on pages which could then be used for later editing. Maybe something like a two button combination to flag a particular paragraph as being of dubious accuracy so that the user could later do some Google searches for references.
Of course another problem with this is the delay in updating a Wikireader. For most reading of Wikipedia it doesn’t matter if the content is 6 months old, so we should expect that most users of the Wikireader don’t have the latest data. The Wikireader company offers an update service of posting a new memory card twice a year [3]. Given postage delays etc we should expect that the average age of the content is about 4 months for people who subscribe to the update service, and probably a lot greater for people who download the updates. The popular pages of Wikipedia change fast, in the space of 4 months a page can change significantly.
In terms of general Wikipedia operation I wonder if it would be beneficial to have a button to flag content as possibly not meeting the Wikipedia guidelines. It seems that the number of people who can recognise low quality pages is going to be significantly higher than the number of people who have the skill and time to fix them. I’m sure that there are many people who would just love to be able to choose from a list of Wikipedia pages that have received many negative votes. Such votes could be stored offline and uploaded later, but again that would rely on having recent content on the reader (it would be annoying for a recently fixed page to keep getting voted down).
One area where offline editing of a Wiki would work well is that of niche Wikis. For example if I downloaded a copy of the Debian Wiki (which would only take a tiny fraction of the space in a Wikireader) then I could easily update it every week and the incidence of other people editing a page in the mean time would often be low. I could write long updates that make significant changes to SE Linux related pages while offline without needing any references and in many cases without much risk of conflicts. Implementing a distributed version control system to manage such updates shouldn’t be difficult in principle, although the VCS might have to run on a laptop or desktop system after taking raw data from the Wikireader (tools like GIT seem memory hungry and might not fit on a small device).
Also Mako refers to the “already indefensibly large gap between the number of readers and editors on Wikipedia“. Like Mako I don’t have a TV watching personality. I agree that it is desirable to facilitate read-write access for everyone, but that doesn’t have to involve write access to Wikipedia. I am not convinced that there is a difference between the number of readers and editors of Wikipedia that indicates a problem here. As something becomes more popular the number of people who use it without being committed to it increases, and it also becomes more integrated into society. I don’t think it’s a problem that many people use their writing time for other tasks such as blogging rather than editing Wikipedia. Wikipedia makes a great reference for blog posts and blog posts drive readers (and thus potential editors) to Wikipedia.
Finally I think we should consider the fact that different people have different skill sets. Maybe the Wikipedia reader base gained a significant portion of the people who have the skills to make good editors a long time ago and now the majority of new users just don’t have the skills. If that is the case then having the ratio of readers to editors change in favor of readers while the number of readers expands would be a good thing. I don’t think that I am being elitist in acknowledging that different people have different skill sets, and that some portion of the population will lack the skills necessary to make good contributions to Wikipedia (good enough to outweigh the mistakes that they make). I think that valuing the contributions of all people in society does not require that we value all contributions to Wikipedia.
John Robb wrote an interesting post about running web sites to target corporations such as Goldman Sachs [1] (such as tracking where it’s employees live).
Naked Capitalism has an interesting post about US investment banks getting preferential access to vaccines [2]. In the comments section some people state an intention to deliberately infect Goldman employees if they get sick.
Rob Blackwell at American Banker writes about a popular iPhone game based around the idea of defending the White House from attacking bankers who try and steal money [3]. The game features a number of ways of killing bankers.
It seems to me that the US bankers have gone way beyond the level of greed that will actually benefit themselves and their actions seem to indicate a death-wish.
As the banks are supposedly too big to fail they should also be too big to be allowed to kill themselves, so maybe we need some sort of corporate suicide-watch. According to a blog post I read when someone is admitted to a psychiatric hospital after a suicide attempt they are watched by video at all times, inspected every 15 minutes, and regularly searched for sharp objects. Maybe part of the bail-out package should have included the US government inspecting the offices of bankers every 15 minutes, watching them at all times by video, and regularly searching them for toxic assets, derivatives that no-one understands, etc. It seems that the TSA employees would rather search for money than weapons [4], so they could be redeployed in searching bank offices. TSA employees never were much good at searching for bombs anyway [5].
I’ve just read an interesting post at Making Light about seat-belts [1].
In Australia seat-belt use is mandatory, you can be fined for failing to wear one – and the police (who help clean up the mess when someone dies on the road) are apparently quite aggressive about enforcement. Even aside from the legal requirement the use of seat-belts is fairly ingrained in Australian culture, people tend to use them even when they won’t get caught.
One of the things I like to do in my spare time is to take unused computer gear from IT companies (which they regard as rubbish) and give it to home users for recreational and educational use. Due to that and my work for some smaller IT companies I’ve helped many people load computer gear into their private cars and observed that most people will not take adequate care unless I coerce them.
A CRT monitor tends to be large and heavy, you wouldn’t want to get hit in the back of the head with one at 60Km/h. With some combinations of monitor and car you can fit a monitor in the front passenger foot-well, but usually the only place a monitor will fit is the back seat. The correct thing to do is to use the seat-belt to strap the monitor in place. It’s most likely that the monitor stand (the only part that allows a seat-belt to be attached) would snap off in the event of a serious crash – but this would at least slow the monitor down. Also don’t put the monitor directly behind your seat if you can avoid it, put it behind the passenger seat. In a collision monitor might be able to push through your seat and cause you a back injury.
Between 1992 and 2006 there were 78,000 acute computer-related injuries treated in US hospital emergency rooms [2]. The number of injuries caused by monitors peaked at 37% of the total in 2003 – this was largely due to monitors falling on people. Even without the speed of a car a monitor can be a dangerous projectile.
Hard drives have a lot of potential to cause damage, they are dense, hard, and the corners often aren’t rounded. Storing them above the back seat behind the driver’s head (as a friend once tried to do) is a really bad idea. Mythbusters showed that a box of tissues isn’t going to kill you in a crash, but a hard drive is much more dangerous. The typical car glove box can store a few drives. If you need to transport a box full then the front passenger foot well is a reasonable place. If your car rolls then that would suck, but it seems that people usually die when they roll their car anyway so just try not to do that.
A serious server (EG 2RU or bigger rack-mount) typically weighs 30Kg or more and is solidly constructed. The size and mass of such a machine makes it extremely difficult to safely store inside a car. The ideal place is the boot, but if that isn’t an option then behind the passenger seat is the next best option.
One final issue that I’ve been wondering about is the safest option for laptops that are in use in a moving car. A 3Kg Thinkpad would have to hurt if it hit you in the back of the head at 60Km/h. The child-seat attachments are solid anchor points that can be used for other things. I wonder if a laptop security cable could be attached to one of the child seat points. According to an exhibit at a science museum I can throw a tennis ball at 115Km/h, so I presume that laptop security cables are designed not to break when someone swings the laptop at that speed. Therefore if a car was driving at a legal speed in Australia before crashing then a laptop security cable should be able to stop the laptop. Preventing the cable from injuring the passenger on the way would be the difficult part.
I’ve just been disappointed to read about the DNI (Defence in the National Interest) web site closing down [1]. The final blog post says “In the meantime, I’ll leave everything up unless we start having more security problems“, but unfortunately they have had a number of security problems in the past. I doubt the ability of a WordPress installation to remain unscathed on the Internet if it’s not upgraded regularly. So I think it’s only a matter of time before a new bad WordPress bug is discovered and DNI goes offline for good.
In the past I did idly consider volunteering to help them run their site, but apart from a lack of spare time there is the issue that a number of their policy positions are things that I strongly disagree with. I can agree with paleo-cons on a number of issues, but there are also significant areas of disagreement.
So it seems that the combination of a lack of skilled system administrators and a lack of good security in their software is reducing their ability to spread their message. While the site content is going to be mirrored on other sites the URLs will break and Google will give it a lower rank. In many ways losing Google ranking is a way of being silenced.
I wonder whether the apparent lack of moderate-right political expression on the Internet is partly due to that demographic having less IT skills than the groups who have centrist to left-wing political views and those who have extreme-right views. Naturally anyone can pay to have someone run their web site, but having to pay raises the barrier to entry and eliminates some of the potential contributors. I think it’s a bad thing for democracy if the only people who get their voices heard are those who have significant amounts of money or technical skill.
One of my hopes for the SE Linux project was that it would increase the longevity of servers while also decreasing the amount of money required to run them. But of course if you have buggy PHP code then there’s not much SE Linux can do to help you.
I recently had the misfortune to be compelled to install Proftpd on SCO Unix. There’s nothing wrong with Proftpd of course, but everything is wrong with SCO.
LDFLAGS=-L/usr/ucblib ./configure –libdir=/usr/ucblib --enable-builtin-getnameinfo
To get it to compile the above ./configure line is needed. It uses /usr/ucblib because having the basic BSD sockets API residing in a non-default directory makes things more exciting. The --enable-builtin-getnameinfo option is needed because the getnameinfo library call in SCO Unix doesn’t work properly. On a real OS I would have downloaded the source to libc to figure out where the problem might be, but on SCO I had no option other than to disable that functionality.
Then once I got it working I had to put UseIPv6 off in the configuration file, otherwise I got the error No Route to Host (from memory) when I tried to start proftpd.
Finally the process was dying from an unhandled SIGALRM every 10 seconds. According to truss (a vastly inferior equivalent to strace) the sigaction() system call was being entered four times to handle SIGALRM (as was reported for every time the application code called sigaction() but the default action of terminating the application remained in place. I ended up running proftpd from inetd which removed the need for the alarm handling code. Then it all worked.
SCO sucks.
Last month Darl McBride was terminated from his position with the SCO group [1]. It’s unfortunate that Darl wasn’t terminated a lot earlier, if so then maybe SCO could have focussed on improving the quality of their products and delivering value for stock holders. Hopefully Darl will be sued by some of the people who lost money when SCO went bankrupt.
It would be good if Darl could also be sued by companies that lost money due to the poor quality of SCO Unix – that means every company that runs SCO servers or that writes software for it. The truly awful nature of SCO Unix is in large part due to the fact that all of SCO’s money was spent on litigation that was well known to be baseless.
|
|
