Welcome to 21-260

Welcome to 21-260 Differential Equations. I'll use this blog to post information and updates about the course. See you in class on Monday.

Vynyl LP's to MP3's

In the olden days, we used to listen to music on vinyl LP records. Nowadays, though, it is much more convenient to listen to music in a digital format. Accordingly, those of us of a certain age are faced with a problem: what to do about that record collection.

During the 1980's, I accumulated a pretty sizable record collection. When CD's were released in the late 80's, I started buying music in that format. I got CD duplicates of many of my most favorite albums. But a lot of others slipped through the cracks.

It is possible to buy turntables designed to connect directly to your computer in order record your music and save it in your desired format. But if you have enough LP's to make this worthwhile you probably already have a turntable. It seems like a waste to buy a new one. In fact it is.

I've had great success ripping my LP's using only: (1) My stereo, specifically a Techniques turntable and amplifier purchased sometime before 1988, (2) a MacBook Pro, and (3) the free application Audacity (If you want to create MP3's, you'll also need the LAME MP3 encoder, also free.) Oh, also (4) a "two RCA to mini-stereo" cable.

Once you've downloaded the software, connect the mini-stereo end of your cable to the "audio in" on your computer. Then connect the RCA ends to a spare audio out on your amplifier. (I used "VCR 2", but you could use the tape deck output if necessary.) From here it's like falling off a bike.

Once you get familiar with Audacity's controls, start playing your favorite record. Open a new Audacity project and click the record button. Adjust the input level until the meter just barely doesn't top out. You can also look at the wave form, the loudest portions should be not quite as tall as possible. Once everything is set, close the track you've been recording, and start a new one by hitting record, play your record and sit back. When the album side ends, click stop, and save the project.

You'll probably want to clean up the recording. I've found that using the "noise removal" and "click removal" to be pretty effective. For the noise removal, select a couple seconds of quiet between songs, or at the end of the record. Choose Effect > Noise Removal, then click "Get Noise Profile". Now select your whole recording. Again, choose Effect > Noise Removal. This time you want to click "Remove Noise". I find moving the slider two spots toward "less", i.e. the 5th of the 15 positions, to remove most of the noise without affecting the quality of the recording too much.

Next, while the whole recording is still selected, choose Effect > Click Removal. I just use the default. Together with the noise removal, this cleans things up very nicely. If your record has a real scratch, this probably won't get rid of it completely, but if your record is in good shape, you can get a very nice recording.

Now for the tedious part. Select each song separately, and choose File > Export Selection as MP3. Fill in all the information in the dialog boxes and save the file somewhere that you can find it easily. Once you've done that, drag all the mp3 files onto the iTunes icon, or do whatever else you do with your mp3's. You're good to go.

Audacity does a great job, but it is free, and there are a few bugs. For instance, if your screen goes to sleep while you record, there is a slight skip in the recording. If all your recording have a skip at about the 1 minute mark, this might be the reason. All in all, though, this seems to be pretty effective.

Bike Log

Yesterday evening, I did a 13 mile ride at Hartwood Acres. I went out with one of the PORC groups. It was a great night. We haven't had much rain lately, so pretty much everything was dry. It was nice an cool, too, which is surprising for the middle of August.

The Enigma Machine

This is sort of old news, but I just dug far enough into my inbox to see it again. The May 30 "The Mathematical Tourist" article on the MAA website is about the Enigma Machine. I think the Enigma Machine is absolutely fascinating. In addition to having the most intriguing name of any technological innovation, the story of it's use in WWII and the allies breaking of the code is more exciting than real history has any right to be. Okay, a bit of hyperbole, but still.

The article linked has a number of links to other interesting and informative sites. I do take exception to the authors comments about Cryptonomicon. Cryptonomicon is not so much a story about the Enigma machine as it is a story about... well it's hard to explain, but the Enigma Machine features prominently. I highly recommend it. I've never read Enigma by Robert Harris, so I can't comment about that.

The Code Book by Simon Singh also has an outstanding chapter on the Enigma Machine.

21-120 Final Wrapup

Well, the semester has drawn to a close. Here are the final statistics for the course. You can see that the final grade cutoffs are

A 74.32
B 62.95
C 52.95
D 41.25

I don't use Blackboard to compute grades, but your final average, unless you have late homeworks, will be the same as your "weighted average" from the blackboard site. At least they ought to be. Until a few moments ago, Exam #3 was categorized as an "assignment" rather than an "exam", which threw off the calculation. I've corrected that though, so now, you should be able to compare your "weighted average" to the cutoffs above to determine your grade. As long as you don't have any late homeworks, that is.

Course Statistics and Graded Homework

Here is a page of statistics for the course so far. You can see (revised (downward)) grade ctuoffs for the three midterm exams, and the computed cutoffs for your cumulative averages. The final grade cutoffs may change somewhat after the final has been graded, but probably not too much.You can compare your "weighted average" from the blackboard site to the Cumulative Average grade cutoffs to see where you stand going into the final.

I think all of you uncollected graded homework is in a box outside my office door (WEH 6214). I think it includes HW#15 for sections A and B, but I'm not sure about Section C.

Finals Week Schedule

Our Final Exam is, of course, at 5:30 on Friday, May 9.

I'm trying to schedule a review session for 1:00-2:30 on Wednesday, May 7. That is a reading day, so most of you should be available.

I'll hold office hours most day's this week. The schedule is:

Monday: 11:30-1:00
Tuesday: 11:30-12:15
Wednesday: Review Session, 1:00-2:30 (tentatively)
Thursday: 11:30-1:00
Friday: 11:30-1:00

Dude This is Totally Awesome

Who would have thought that 216 magnetic spheres would be so cool.

Another Difference Engine

My last post about a real functioning Difference Engine reminded me of William Gibson's The Difference Engine, with which I was much less impressed.

A long time ago, when I had just finished reading Neuromancer, I thought The Difference Engine looked pretty cool. I'm not exactly sure what it was about, but it wasn't about Babbage's Difference Engine. As I recall, Charles Babbage is one of the characters, but he is unsympathetic to say the least. Do yourself a favor; read Neuromancer, but give this one the go by.

As an aside, this follows one of my cardinal Rules for Reading Fiction: Books by two authors are terrible.

Babbage Difference Engine #2

I, like many math/science types, have always been fascinated by Charles Babbage's Difference Engines. They were undeniably revolutionary when he designed them in 1821 and 1849. One can only imagine what might have happened had they been built.

Well, now someone has built Difference Engine Engine #2, and it is on display at the Computer History Museum in San Jose (beginning May 10).