Engineering FM – Part 4

Time for the exciting fourth instalment of my ongoing series on engineering at a small community radio station launching an FM service for the first time. In this post I’m going to be looking (somewhat briefly) at processing.

There’s been a place for processors ever since radio has existed, to make sure that audio input to a modulator doesn’t exceed the modulator’s input limits without making the audio itself sound bad. This typically involved an automatic gain control circuit, or AGC. As time went by, these evolved into multiband AGCs, processing in typically four chunks for LF, LMF, HMF, and HF audio segments. Clippers and limiters were also used to protect equipment but as stations aimed for a competitive edge processors became used to make stations sound louder and punchier by maximising the amount of modulation used at any time. Continue reading Engineering FM – Part 4

Processing, Mediawiki, and force-directed layouts

Happily, the EVE Online official wiki- the Evelopedia– has now gone into public beta. You can imagine, then, that there’s a lot of activity on it. I’m something of a Mediawiki fan; I’m currently using a very hacked-upon version on my laptop for notetaking and information storage, and used to contribute quite a bit to Wikinews/Wikipedia. So when the Evelopedia went live I was at it like a shot.

The recent changes pages of Mediawiki list the most recent changes to the wiki, providing information on the page edited, the edit made, the date of the edit, and the user making the edits. It’s simple enough to read through, but behind the monotonous list there’s a much more interesting picture to be found.

The final(ish) recent changes app, having been running for a night.
The final(ish) recent changes app, having been running for a night.

This is my first real finished product done with Processing. It grabs the RSS feed of changes, imports each change by adding a change node, an author node, and a page node. If the author or page already exists, it links them again via the newly added change and adds weight to the author and page nodes. It then queries the RSS feed every minute to grab fresh data, and imports any new changes.
What was going on last night? This!
The layout of the graphs is performed automatically using a force-directed layout. I used a simple physics library for Processing (traer.physics), and added the physics framework to my existing Node framework originally designed for the EVE Tactical Map. Every particle has repulsion to every other particle, except for particles they are linked to- they have an attraction and a spring whose length is defined by the number of links of the parent particle.

Evelopedia Recent Changes - Early Version
Depending on what the simulation damping setting is, it can take from 10 seconds to 5 minutes for the simulation to become stable and settle down- it’s all done in realtime, with new changes randomly appearing and being pulled towards their appropriate author/page articles.


Evelopedia Recent Change Monitor – Trailer from James Harrison on Vimeo.

Once I get the source in shape (It’s a single 310-line .pde file right now with few comments and no error handling) I’ll probably open this up for all who want to have a play with it. I’d be interested to see what a force-directed layout method would make of the EVE map, so I might end up backporting my code to the Tactical Map to see what happens.