+1 for the Stevens and Perlman books. I haven't read Halsall's book, but I might now that I see it placed next to those two.

It is multiplication. The mixer in radio is nonlinear so that the sum and product signals result from the trig identity: sin(theta)*sin(phi) = cos(theta-phi)/2 - cos(theta+phi)/2. Additive combination of signals does not produce lower frequencies that could be filtered out.

I take that back. Heterodyne is non-linear phenomenon (multiplication of signals, rather than addition). If dog whistle beats are audible, the explanation is different.

Wrong. The phenomenon is real -- physical, not phycho-acoustic. It is the pressure-wave analog of a radio heterodyne.

And those beats (the mixing products that exist below the sampling frequency) will be captured on the digital recording. There are also high frequency product at the sum of the original frequencies which will be lost, but even dogs won't hear them.

This isn't Zimmerman's first time around the block. His Zrtp protocol for SIP (VOIP) security includes Short Authentications Strings which can be communicated by voice or even out of channel, as well as shared secrets from previous connections. These offer reasonable protection against man in the middle attacks.

Shouldn't we first ask whether an icon is helpful at all here? I just spent 5 minutes looking for a save icon in the applications included in OS X 10.6.8 and can't find a single one.

Actually, OS X is Unix. One might say that the Darwin (OS X) kernel is a descendant of BSD, since Unix services are implemented in kernel using BSD (derived) code. On the other hand, the kernel is based on Mach 3 which was historically run as a microkernel, but is now packed so full of high level Unix code that it is anything but "micro".

Of course, OS X implements other capabilities (I/O Kit, Cooa, etc) in addition to those in the Unix spec./p

You got me. How 'bout we try Jitsi.

Back when I was in school, we has Schaum's outlines, and we liked them. Search the internet for explanations if you have trouble, but working through a ton of problems n paper will give you proficiency and confidence.

Many politicians are overwhelmed by email campaigns at the moment, and are paying more attention to phone calls. At least that's what my politically connected friends tell me.

I think about Apple's insane control issues every time I have to re-install OS X (which I did once for testing purposes). My outrage at not being required to type long registration codes and then have the OS phone home for validation is unspeakable.

Bravo, good sir. Bravo.

I absolutely agree with everything you just said.

Honestly, I don't believe learning C helps one to programs in Prolog, Scheme, Haskell, Smalltalk or other non-traditional, but at times very handy, programming languages. If you insist on starting out with low level concepts, buy the kid a copy of Knuth Vol. 1 and work through some example on a MIX simulator!

Pointers and stacks are not required organizational structures for progamming languages. I'm qualified to comment, having worked on the stack-less, continuation passing style back end of the SML/NJ compiler way back when. If you approach programming assuming these as fundamental, you limit your vision of what is possible. The way I see it, teaching a kid to avoid incredibly useful modern features like garbage collection and first class functions just seems cruel.

A self-motivated 11 year old has plenty of time to learn c++. My high school band teacher offered sage advice when asked about accepting a gig when you don't know the style of music: "Of course you take the gig! You then spend every spare minute learning a set and you show up ready to perform." The same approach worked for me with regard to programming languages. I never lied about my experience, but I have often promised to be ready to perform in a new language, and I have never disappointed. Of course, you don't get there out of complacency, I had read Stroustrop and knew the concepts of C++ long before writing a line of code and accepting my current MFC/COM/C++ job. If our 11 year old is going to be a great programmer, he'll do the equivalent because remaining ignorant will simple not be acceptable for him.

"Harder than other languages" is an understatement. One apt critic describes C++ thusly: " It's just beastly and horrendously ugly - confuses students like heck (huh? copy constructors? virtual destructors?)"

Nah man, snakes are cool. "Playing with Ruby" makes it sound like your eleven-year-old hired a whore, or perhaps a drag-queen.