Download Efficient emulation of tape-like delay modulation behavior A significant part of the appeal of tape-based delay effects is the manner in which the pitch of their output responds to changes in delay-time. Straightforward approaches to implementation of delays with tape-like modulation behavior result in algorithms with time complexity proportional to the tape speed, leading to noticeable increases of CPU load at smaller delay times. We propose a method which has constant time complexity, except during tape speedup transitions, where the complexity grows logarithmically, or, if proper antialiasing is desired, linearly with respect to the speedup factor.
Download A Combined Model for a Bucket Brigade Device and its Input and Output Filters Bucket brigade devices (BBDs) were invented in the late 1960s as a method of introducing a time-delay into an analog electrical circuit. They work by sampling the input signal at a certain clock rate and shifting it through a chain of capacitors to obtain the delay. BBD chips have been used to build a large variety of analog effects processing devices, ranging from chorus to flanging to echo effects. They have therefore attracted interest in virtual analog modeling and a number of approaches to modeling them digitally have appeared. In this paper, we propose a new model for the bucket-brigade device. This model is based on a variable samplerate, and utilizes the surrounding filtering circuitry found in real devices to avoid the need for the interpolation usually needed in such a variable sample-rate system.
Download Waveshaping with Norton Amplifiers: Modeling the Serge Triple Waveshaper The Serge Triple Waveshaper (TWS) is a synthesizer module designed in 1973 by Serge Tcherepnin, founder of Serge Modular Music Systems. It contains three identical waveshaping circuits that can be used to convert sawtooth waveforms into sine waves. However, its sonic capabilities extend well beyond this particular application. Each processing section in the Serge TWS is built around what is known as a Norton amplifier. These devices, unlike traditional operational amplifiers, operate on a current differencing principle and are featured in a handful of iconic musical circuits. This work provides an overview of Norton amplifiers within the context of virtual analog modeling and presents a digital model of the Serge TWS based on an analysis of the original circuit. Results obtained show the proposed model closely emulates the salient features of the original device and can be used to generate the complex waveforms that characterize “West Coast” synthesis.