Download Sound synthesis using an allpass filter chain with audio‐rate coefficient modulation This paper describes a sound synthesis technique that modulates the coefficients of allpass filter chains using audio-rate frequencies. It was found that modulating a single allpass filter section produces a feedback AM–like spectrum, and that its bandwidth is extended and further processed by non-sinusoidal FM when the sections are cascaded. The cascade length parameter provides dynamic bandwidth control to prevent upper range aliasing artifacts, and the amount of spectral content within that band can be controlled using a modulation index parameter. The technique is capable of synthesizing rich and evolving timbres, including those resembling classic virtual analog waveforms. It can also be used as an audio effect with pitch-tracked input sources. Software and sound examples are available at http://www.acoustics.hut.fi/publications/papers/dafx09-cm/
Download Alias-free Virtual Analog Oscillators Using a Feedback Delay Loop The rich spectra of classic waveforms (sawtooth, square and triangular) are obtained by discontinuities in the waveforms or their derivatives. At the same time, the discontinuities lead to aliasing when the waveforms are digitally generated. To remove or reduce the aliasing, researchers have proposed various methods, mostly based on limiting bandwidth or smoothing the waveforms. This paper introduces a new approach to generate the virtual analog oscillators with no aliasing. The approach relies on generating an impulse train using a feedback delay loop, often used for the physical modeling of musical instruments. Classic waveforms are then derived from the impulse train with a leaky integrator. Although the output generated by this method is not exactly periodic, it perceptually sounds harmonic. While additional processing is required for time-varying pitch shifting, resulting in some high-frequency attenuation when the pitch changes, the proposed method is computationally more efficient than other algorithms and the high-frequency attenuation can be also adjusted.
Download Spectral Dealy Filters with Feedback Delay Filters with Feedback and Time-Varying Coefficients A recently introduced structure to implement a continuously smooth spectral delay, based on a cascade of first-order allpass filters and an equalizing filter, is described and the properties of this spectral delay filter are reviewed. A new amplitude envelope equalizing filter for the spectral delay filter is proposed and the properties of structures utilizing feedback and/or time-varying filter coefficients are discussed. In addition, the stability conditions for the feedback and the time-varying structures are derived. A spectral delay filter can be used for synthesizing chirp-like sounds or for modifying the timbre of arbitrary audio signals. Sound examples on the use of the spectral delay filters utilizing the structures discussed in this paper can be found at http://www.acoustics.hut. fi/publications/papers/dafx09-sdf/.