Program to Produce and Filter Sound Waves

To experiment with the timbres that can be synthesized with our high Q filters, we wrote a test program, filter.cpp. The program runs on an 800mHz PC running a Linux operating system. The program can

• Compute up to 200 filters whose outputs are summed and sent to a d-to-a converter (16bit, monaural, 44.1kHz) running as a real-time synthesis process.

• Accept impulse inputs to blocks of filters to generate homogeneous filter responses.

• Accept samples from a sound wave put through an a-to-d converter (16bit, monaural, 44.1kHz) running as a real-time effects processor.

• Accept samples from .wav files in the computer hard disk as input.

• Dynamically change the resonant frequencies and damping of blocks of filters in response to either computer keyboard key presses or midi input commands from a midi keyboard.

• Display either waveforms or envelopes of various sampled waves in the computer program

Computations are done in double precision floating point arithmetic. The program has not been carefully optimized. Only about 30 percent of the computer power seems to run all 200 filters.

Tests where parametric changes (both frequencies and decay times) of blocks of filters were suddenly changed showed that neither visible nor audible transients were produced by the parametric changes. Thus it would appear that both frequency and decay can be used as rapidly changing time-varying parameters to form ``compositional lines'' in compositions.

In the presentation of this paper at the SMAC 03 meeting, we will demonstrate various timbres and effects that can be produced by the filters.