Synthesizers—Part 2

     Last month we looked at additive, subtractive and FM synthesizers. This month were going to explore physical modeling synthesizers. These synthesizers have only come into the forefront recently as the processing power require was not available until then. What physical modeling synths do is to take the waveform that a particular instrument produces and model it digitally for every note, dynamic level, etc. so that the sound the synthesizer produces is as close as possible to the original sound. It is a departure from the earlier types of synthesis that tried to approximate the sounds of different instruments and instead came up with entirely new sounds.

      To understand how physical modeling is done, we have to first understand the nature of a musical note. In most cases, musical notes consist of the fundamental note, let’s use A for instance and several (in some cases, many) harmonic notes the are even number multiples of the frequency of the original note. Since we chose A, we’ll choose the frequency as 440 cycles per second (hz). The harmonics of this note would be  55, 110, 220, 880, 1760 and so on. What determines the timbre (distinctive qualities) of the note is how many of the harmonics are present and at what volume.

      Physical modeling takes all the characteristics of the note and quantifies them so that they can be reproduced accurately. It also takes dynamics into account because as the note is louder or softer, different harmonics come into play. Also, in the case of a piano, or other multi stringed instrument, some of the other strings can vibrate sympathetically under the right conditions and that has to be programmed into the profile as well. In addition to being used in synthesizers, it has been widely used in the guitar world to replicate amplifier and speaker cabinet combinations and effects. Roland’s VG-88 takes this a step further by including acoustic and electric guitar modeling along with tuning on the fly without turning a tuning key.

      Before we had the fast processors of today, a physical modeling synthesizer was strictly a laboratory curiosity that it might take minutes for it to produce one note. The whole performance would have to be programmed in advance and then the computer would churn away producing a file that could be played back later. With today’s fast processors and advanced programming, it only takes milliseconds. Sample playback remains the favorite for most people because you are playing back the actual sound the instrument produces but I would venture to bet that as technology increases, physical modeling will give it a run for its money. It’s just a matter of being able to quantify all the  aspects of the timbral, harmonic and dynamic envelopes and reproduce them accurately.


Next month—phase distortion.

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