Day 2

Music 220a

Fundamentals of Computer Generated Sound - Chris Chafe

According to the professor, 220a is a kind of programming course.  It is apparently designed to convey the basic techniques of digital sound synthesis and computer music composition, using ChucK as a pedagogical tool (a task for which I believe it is optimally suited).  The content of this course seems pretty straight-forward for me, but it's been three years since I've covered these topics in a classroom.  I'm looking forward to spending long nights curled up with a midi controller and my laptop, making bizarre bleeps and bloops into the night for academic credit.  One thing strikes me as odd, though.  The text for this course is Perry Cook's Real Sound Synthesis.  I actually read it this the summer, and it is rather in-depth, mostly focused on physical modeling.  Maybe there is more to this class than meets the eye.  We shall see.

The second half of the lecture took place in the Knoll Concert Hall, a room that is more reminiscent of a small chapel than a concert hall.  It sports 16 channels of ADAM speakers, eight around the walls and eight hung from the ceiling.  The presentation was a ~15 minute live computer music performance by Fernando Lopez-Lezcano.  The piece, entitled "A Very Fractal Cat" was played on a midi keyboard with foot pedals and switches.  The sound was like being inside a piano when someone sits down to play some atonal music, and all of a sudden the strings emit sonic smoke that wafts up as the extremely high partials decay.  Then the whole damn thing catches fire.  It was a good piece, but I wrote a note to myself during the performance: NO COMPUTER MUSIC BEFORE NOON!

Music 320

Introduction to Digital Audio Signal Processing - Jonathan Abel and David Berners

I guess this is the class I've been waiting for.  The signal processing series, taught by Abel/Berners or Julius O. Smith, represents my reason for being at CCRMA in the first place.  Today was really just a bunch of hand-waving over the field of signal processing.  Jon gave a very basic introduction to perception (cochlea, basilar membrane), digital audio signals, complex exponentials, sinusoids, and resynthesis.  Notwithstanding the elemental nature of today's lecture, during which I found myself installing Octave packages on my laptop, I learned something really important about dB conversion.

I had been confused by linear to dB conversions that sometimes involve 20*log something and sometimes 10*log something.  I guess I just wasn't looking closely enough.  Jon pointed out today that given a signal x(t), the dB representation of that signal is 10*log( abs( x(t) )^2) but is sometimes represented by 20*log( abs( x(t) ) ).  This follows from one the logarithmic identities, but I still wondered why one would choose to use one form over the other.  First of all, we need to look at why  the the dB system is the way it is.  In the first version of the dB calculation, the input signal is squared because the measurement is taken on the signal's power.  The power of two can be cancelled by the identity, and I suspect this form is desirable in computer systems because it removes the squaring operation from the computation.