Download Exponential Frequency Modulation Bandwidth Criterion for Virtual Analog Applications Cross modulation or Exponential FM is a sound synthesis technique associated with modular analog subtractive synthesizers. It differs from the more well-known linear FM synthesis technique in that the modulation is an exponential function of the control voltage. Its spectrum shape is more complex, thus giving it a larger bandwidth with respect to the modulation depth. Thus, the prevention of aliasing distortion requires different conditions than Carson’s rule as used with linear FM. A suitable equation will be presented in this paper.
Download Vector Phaseshaping Synthesis This paper introduces the Vector Phaseshaping (VPS) synthesis technique, which extends the classic Phase Distortion method by providing flexible means to distort the phase of a sinusoidal oscillator. This is achieved by describing the phase distortion function using one or more breakpoint vectors, which are then manipulated in two dimensions to produce waveshape modulation at control and audio rates. The synthesis parameters and their effects are explained, and the spectral description of the method is derived. Certain synthesis parameter combinations result in audible aliasing, which can be reduced with a novel aliasing suppression algorithm described in the paper. The extension is capable of producing a variety of interesting harmonic and inharmonic spectra, including for instance, formant peaks, while the two-dimensional form of the control parameters is expressive and is well suited for interactive applications.
Download Automatic Partial Extraction From the Modal Distribution The Modal Distribution (MD) is a time-frequency distribution specifically designed to model the quasi-harmonic, multisinusoidal, nature of music signals and belongs to the Cohen general class of time-frequency distributions. The problem of signal synthesis from bilinear time-frequency representations such as the Wigner distribution has been investigated [1,14] using methods which exploit an outer-product interpretation of these distributions. Methods of synthesis from the MD based on a sinusoidal-analysis-synthesis procedure using estimates of instantaneous frequency and amplitude values have relied on a heuristic search ‘by eye’ for peaks in the time-frequency domain [2,7,8]. An approach to detection of sinusoidal components with the Wigner Distribution has been investigated in [15] based on a comparison of peak magnitudes with the DFT and STFT. In this paper we propose an improved frequency smoothing kernel for use in MD partial tracking and adapt the McCauley-Quatieri sinusoidal analysis procedure to enable a sum of sinusoids synthesis. We demonstrate that the improved kernel enhances automatic partial extraction and that the MD estimates of instantaneous amplitude and frequency are preserved. Suggestions for future extensions to the synthesis procedure are given.
Download Metamorph: Real-Time High-Level Sound Transformations Based on a Sinusoids Plus Noise Plus Transients Model Spectral models provide ways to manipulate musical audio signals that can be both powerful and intuitive, but high-level control is often required in order to provide flexible real-time control over the potentially large parameter set. This paper introduces Metamorph, a new open source library for high-level sound transformation. We describe the real-time sinusoids plus noise plus transients model that is used by Metamorph and explain the opportunities that it provides for sound manipulation.
Download Virtual Analog Oscillator Hard Synchronisation: Fourier series and an efficient implementation This paper investigates a number of digital methods to produce the Analog subtractive synthesis effect of ‘Hard Synchronisation.’ While the original effect is produced by an explicit waveform phase reset, other approaches are given that produce an equivalent output. In particular, based on measurements taken from a real-analog synthesizer, a comb filtering model is proposed. This description ties in with earlier work but here an explicit structure is provided. This filter-based approach is then shown to be far more computationally efficient than the synchronisation by phase reset. This efficiency is at a minor cost as it is shown that it has a minimal impact on the sonic accuracy.
Download Synthesis of Resonant Sounds with a Heterodyne Model This paper considers the generation of resonant waveforms from a number of perspectives. Commencing with the well-known source filter model it introduces a more advantageous heterodyne interpretation. Some variations on the basic design and comparisons with previous methods are then given. An analysis on the use of three different digital music filter structures for resonance synthesis is made, followed by an example showing how timbrally rich Frequency Modulated resonant waveforms can be synthesized.
Download Digital Audio Effects on Mobile Platforms This paper discusses the development of digital audio effect applications in mobile platforms. It introduces the Mobile Csound Platform (MCP) as an agile development kit for audio programming in such environments. The paper starts by exploring the basic technology employed: the Csound Application Programming Interface (API), the target systems (iOS and Android) and their support for realtime audio. CsoundObj, the fundamental class in the MCP toolkit is introduced and explored in some detail. This is followed by a discussion of its implementation in Objective-C for iOS and Java for Android. A number of application scenarios are explored and the paper concludes with a general discussion of the technology and its potential impact for audio effects development.
Download A Streaming Audio Mosaicing Vocoder Implementation This paper introduces a new extension to the concept of Audio Mosaicing, a process by which a set of unrelated sounds are blended together to form a new audio stream of shared sonic characteristics. The proposed approach is based on the algorithm that underlies the well-known channel vocoder, that is, it splits the input signals into frequency bands, which are then processed individually, and then recombined to form the output. In a similar manner, our mosaicing scheme first uses filterbanks to decompose the set of input audio segments. Then, it introduces the use of Dynamic Time Warping to perform the matching process across the filterbank outputs. Following this, the re-synthesis stage includes a bank of Phase Vocoders, one for each frequency band to facilitate targeted spectral and temporal musical effects prior to recombination. Using multiple filterbanks means that this algorithm lends itself well to parallelisation and it is also shown how computational efficiencies are achieved that permit a real-time implementation.
Download Examining the Oscillator Waveform Animation Effect An enhancing effect that can be applied to analogue oscillators in subtractive synthesizers is termed Animation, which is an efficient way to create a sound of many closely detuned oscillators playing in unison. This is often referred to as a supersaw oscillator. This paper first explains the operating principle of this effect using a combination of additive and frequency modulation synthesis. The Fourier series will be derived and results will be presented to demonstrate its accuracy. This will then provide new insights into how other more general waveform animation processors can be designed.
Download Streaming Spectral Processing with Consumer-Level Graphics Processing Units This paper describes the implementation of a streaming spectral processing system for realtime audio in a consumer-level onboard GPU (Graphics Processing Unit) attached to an off-the-shelf laptop computer. It explores the implementation of four processes: standard phase vocoder analysis and synthesis, additive synthesis and the sliding phase vocoder. These were developed under the CUDA development environment as plugins for the Csound 6 audio programming language. Following a detailed exposition of the GPU code, results of performance tests are discussed for each algorithm. They demonstrate that such a system is capable of realtime audio, even under the restrictions imposed by a limited GPU capability.