Tutorials and Topics - Peabody Computer Music

Tutorial 2Fundamentals:Adjustable oscillatorTechnical detail: Any change in the over-all amplitude of a signalintroduces some amount of distortion during the time when the amplitudeis changing. (The shape of the waveform is actually changed during thattime, compared with the original signal.) Whether this distortion is objectionabledepends on how sudden the change is, how great the change inamplitude is, and how complex the original signal is. A small amount ofsuch distortion introduced into an already complex signal may go largelyunnoticed by the listener. Conversely, even a slight distortion of a verypure original signal will add partials to the tone, thus changing its timbre.In the preceding example, the amplitude of a sinusoidal tone decreased byhalf (6 dB) in 5 milliseconds. Although one might detect a slight change oftimbre as the amplitude drops, the shift is not drastic enough to be heardas a click. If, on the other hand, the amplitude of a sinusoid increaseseightfold (18 dB) in 5 ms, the change is drastic enough to be heard as apercussive attack.An eightfold (18 dB) increase in 5 ms creates a percussive effect64