Download Non-Linear Digital Implementation of the Moog Ladder Filter This paper presents a non-linear digital implementation of the Moog ladder filter. The implementation is relatively efficient and suitable for inclusion into real-time systems, for example virtual analog synthesizers. The analog circuit is analyzed to produce a differential equation. This equation is solved using Euler’s method, and the result is shown to be equivalent to a cascade of first order IIR sections with embedded non-linearities. Finally, the filter structure is modified to improve tuning.
Download Enhanced digital models for analog modulation effects This paper presents digital models for analog phaser and flanger / chorus effects. The structure of analog phasers is reviewed. The operation of two phaser implementations is analyzed and nonlinear digital models are presented for them. The models are based on cascades of one-pole filters with embedded nonlinearities and are suitable for real-time implementation. Modifications to standard digital flanger / chorus effect are also presented. A method to warp the delay time to more closely resemble the behavior of bucket brigade delays is presented. Also a simple model for companders used in such analog effect units is presented.
Download POWERWAVE: a high performance Single Chip Interpolating Wavetable Synthesizer In this paper we introduce the single chip implementation of a 16 voices wavetable synthesizer. All digital functions (control and waveform generation) are contained in a single platform FPGA chip (Xilinx Virtex 2 Pro). Only the digital to analog conversion is done by a standard 96 kHz audio DAC (AD 1785). In the first version the synthesizer is controlled via standard RS 232 interface.