Digital Modeling of Analog Effect Circuits

While SPICE circuit simulation software gives researchers and industry accurate information regarding the behavior and characteristics of circuits, the auditory effect of SPICE circuit simulation on audio circuits is not well documented. This project takes a thoroughly analyzed and popular audio effect circuit called the Ibanez Tubescreamer and simulates its distortion effect on a .wav file in order to hear the effect of SPICE simulation. Specifically, the TS-808 schematic is drawn in the SPICE program LTSPICE and simulated using generated sinusoids and recorded .wav files. Specific components are imported using .MODEL and .SUBCKT to accurately represent the diodes, bipolar transistors, op amps, and other components in order to hear how each component affects the response. Various transient responses are extracted as .wav files and assembled as figures in order to characterize the result of the circuit on the input. Once the actual circuit is built and debugged, all of the same transient analysis is applied and then compared to the SPICE simulation figures gathered in the digital simulation. These results are then compared along with a subjective hearing test of the digital simulation and analog circuit in order to test the validity of the SPICE simulations. The digital simulations reveal that the distortion follows the signature characteristics of Ibanez Tubescreamer which shows that SPICE simulation will give insight into the real effects of audio circuits modeled in SPICE programs. Diodes--such as Silicon, Germanium, Zener, Red LEDs and Blue LEDs--can dramatically change the waveforms and sound of the inputs within the circuit where as the Op-amps--such as the JRC4558, TL072, and NE5532--have little to no effect on the waveforms and subjective effects on the output .wav files. After building the circuit and hearing the difference between the analog circuit and digital simulation, the differences between the two are apparent but very similar in nature--proving that the SPICE simulation can give meaningful insight into the sound of the actual analog circuit. Some of the differences can be explained by the variance of equipment and environment used in recording and playback. Since this project did not use high fidelity audio recording equipment and consistency in the equipment used for playback, it is uncertain if the simulation and actual circuit could be classified as completely accurate. Any further work on the project would be recording and playing back in a constant environment and looking into a wider range of specific components instead of looking into one permutation.