Physical modeling is a new synthesis technique which creates sound using mathematical models of actual musical instruments. These models are computationally efficient and allow real-time control and musical expression through a small number of natural parameters. Algorithms that simulate plucked strings, woodwind, brass, and other instruments have been developed and implemented in a real-time, DSP-based synthesizer. These algorithms are described and parameter estimation results based on analysis of real instruments are presented. Results show that physical model parameters and corresponding excitation signals can be found from analysis. Models so derived are not only accurate representations of the sound, but are also expressive and controllable like the instruments they model. A commercial, polyphonic, multitimbral music synthesizer is described which uses physical modeling as one of its synthesis methods. In this keyboard, custom DSPs provide an unprecedented amount of synthesis power and flexibility. Practical issues of implementation and real-time control are discussed and demonstrated. For example, real-time control of pitch, damping, dispersion, and pick location are demonstrated for a guitar model. A short demo that shows the expressiveness and realism of physical modeling is presented.