- <title>Debian used in the subway info screens in Oslo, Norway</title>
- <link>http://people.skolelinux.org/pere/blog/Debian_used_in_the_subway_info_screens_in_Oslo__Norway.html</link>
- <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Debian_used_in_the_subway_info_screens_in_Oslo__Norway.html</guid>
- <pubDate>Fri, 2 Mar 2018 13:10:00 +0100</pubDate>
- <description><p>Today I was pleasantly surprised to discover my operating system of
-choice, Debian, was used in the info screens on the subway stations.
-While passing Nydalen subway station in Oslo, Norway, I discovered the
-info screen booting with some text scrolling. I was not quick enough
-with my camera to be able to record a video of the scrolling boot
-screen, but I did get a photo from when the boot got stuck with a
-corrupt file system:
-
-<p align="center"><a href="http://people.skolelinux.org/pere/blog/images/2018-03-02-ruter-debian-lenny.jpeg"><img align="center" width="40%" src="http://people.skolelinux.org/pere/blog/images/2018-03-02-ruter-debian-lenny.jpeg" alt="[photo of subway info screen]"></a></p>
-
-<p>While I am happy to see Debian used more places, some details of the
-content on the screen worries me.</p>
-
-<p>The image show the version booting is 'Debian GNU/Linux lenny/sid',
-indicating that this is based on code taken from Debian Unstable/Sid
-after Debian Etch (version 4) was released 2007-04-08 and before
-Debian Lenny (version 5) was released 2009-02-14. Since Lenny Debian
-has released version 6 (Squeeze) 2011-02-06, 7 (Wheezy) 2013-05-04, 8
-(Jessie) 2015-04-25 and 9 (Stretch) 2017-06-15, according to
-<a href="https://en.wikipedia.org/wiki/Debian_version_history">a Debian
-version history on Wikpedia</a>. This mean the system is running
-around 10 year old code, with no security fixes from the vendor for
-many years.</p>
-
-<p>This is not the first time I discover the Oslo subway company,
-Ruter, running outdated software. In 2012,
-<a href="http://people.skolelinux.org/pere/blog/Er_billettautomatene_til_kollektivtrafikken_i_Oslo_uten_sikkerhetsoppdateringer_.html">I
-discovered the ticket vending machines were running Windows 2000</a>,
-and this was
-<a href="http://people.skolelinux.org/pere/blog/Fortsatt_ingen_sikkerhetsoppdateringer_for_billettautomatene_til_kollektivtrafikken_i_Oslo_.html">still
-the case in 2016</a>. Given the response from the responsible people
-in 2016, I would assume the machines are still running unpatched
-Windows 2000. Thus, an unpatched Debian setup come as no surprise.</p>
-
-<p>The photo is made available under the license terms
-<a href="http://creativecommons.org/licenses/by/4.0/">Creative Commons
-4.0 Attribution International (CC BY 4.0)</a>.</p>
+ <title>Measuring the speaker frequency response using the AUDMES free software GUI - nice free software</title>
+ <link>http://people.skolelinux.org/pere/blog/Measuring_the_speaker_frequency_response_using_the_AUDMES_free_software_GUI___nice_free_software.html</link>
+ <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Measuring_the_speaker_frequency_response_using_the_AUDMES_free_software_GUI___nice_free_software.html</guid>
+ <pubDate>Mon, 22 Oct 2018 08:40:00 +0200</pubDate>
+ <description><p><img src="http://people.skolelinux.org/pere/blog/images/2018-10-22-audmes-measure-speakers.png" align="right" width="40%"/></p>
+
+<p>My current home stereo is a patchwork of various pieces I got on
+flee markeds over the years. It is amazing what kind of equipment
+show up there. I've been wondering for a while if it was possible to
+measure how well this equipment is working together, and decided to
+see how far I could get using free software. After trawling the web I
+came across an article from DIY Audio and Video on
+<a href="https://www.diyaudioandvideo.com/Tutorial/SpeakerResponseTesting/">Speaker
+Testing and Analysis</a> describing how to test speakers, and it listing
+several software options, among them
+<a href="https://sourceforge.net/projects/audmes/">AUDio MEasurement
+System (AUDMES)</a>. It is the only free software system I could find
+focusing on measuring speakers and audio frequency response. In the
+process I also found an interesting article from NOVO on
+<a href="http://novo.press/understanding-speaker-specifications-and-frequency-response/">Understanding
+Speaker Specifications and Frequency Response</a> and an article from
+ecoustics on
+<a href="https://www.ecoustics.com/articles/understanding-speaker-frequency-response/">Understanding
+Speaker Frequency Response</a>, with a lot of information on what to
+look for and how to interpret the graphs. Armed with this knowledge,
+I set out to measure the state of my speakers.</p>
+
+<p>The first hurdle was that AUDMES hadn't seen a commit for 10 years
+and did not build with current compilers and libraries. I got in
+touch with its author, who no longer was spending time on the program
+but gave me write access to the subversion repository on Sourceforge.
+The end result is that now the code build on Linux and is capable of
+saving and loading the collected frequency response data in CSV
+format. The application is quite nice and flexible, and I was able to
+select the input and output audio interfaces independently. This made
+it possible to use a USB mixer as the input source, while sending
+output via my laptop headphone connection. I lacked the hardware and
+cabling to figure out a different way to get independent cabling to
+speakers and microphone.</p>
+
+<p>Using this setup I could see how a large range of high frequencies
+apparently were not making it out of my speakers. The picture show
+the frequency response measurement of one of the speakers. Note the
+frequency lines seem to be slightly misaligned, compared to the CSV
+output from the program. I can not hear several of these are high
+frequencies, according to measurement from
+<a href="http://freehearingtestsoftware.com">Free Hearing Test
+Software</a>, an freeware system to measure your hearing (still
+looking for a free software alternative), so I do not know if they are
+coming out out the speakers. I thus do not quite know how to figure
+out if the missing frequencies is a problem with the microphone, the
+amplifier or the speakers, but I managed to rule out the audio card in my
+PC by measuring my Bose noise canceling headset using its own
+microphone. This setup was able to see the high frequency tones, so
+the problem with my stereo had to be in the amplifier or speakers.</p>
+
+<p>Anyway, to try to role out one factor I ended up picking up a new
+set of speakers at a flee marked, and these work a lot better than the
+old speakers, so I guess the microphone and amplifier is OK. If you
+need to measure your own speakers, check out AUDMES. If more people
+get involved, perhaps the project could become good enough to
+<a href="https://bugs.debian.org/910876">include in Debian</a>? And if
+you know of some other free software to measure speakers and amplifier
+performance, please let me know. I am aware of the freeware option
+<a href="https://www.roomeqwizard.com/">REW</a>, but I want something
+that can be developed also when the vendor looses interest.</p>