All-digital audio chains

Using analytic PCM-to-PWM mapping, combined with a novel method for eliminating PWM-induced distortions (“Jithering”), a distortion-free, all-digital and high-quality PWM coder was developed. High efficiency and performance is achieved at switching frequencies between 44.1-176.4kHz. A Field Programmable Gate Array - based environment was used for the implementation of the PWM converter, which is suitable for any digital audio applications.

Although uniformly sampled pulse width modulation (UPWM) represents a very efficient digital audio coding scheme for digitalto-analog conversion and full-digital amplification, it suffers from strong harmonic distortions, as opposed to benign nonharmonic artifacts present in analog PWM (naturally sampled PWM, NPWM). Complete elimination of these distortions usually requires excessive oversampling of the source PCM audio signal, which results to impractical realizations of digital PWM systems. In this paper, a description of digital PWM distortion generation mechanism is given and a novel principle for their minimization is proposed, based on a process having some similarity to the dithering principle employed in multibit signal quantization. This conditioning signal is termed "jither" and it can be applied either in the PCM amplitude or the PWM time domain. It is shown that the proposed method achieves significant decrement of the harmonic distortions, rendering digital PWM performance equivalent to that of source PCM audio, for mild oversampling (e.g., ×4) resulting to typical PWM clock rates of 90 MHz.

Although uniformly sampled pulse width modulation (UPWM) represents a very efficient digital audio coding scheme for digital- to-analog conversion and full-digital amplification, it suffers from strong harmonic distortions, as opposed to benign non- harmonic artifacts present in analog PWM (naturally sampled PWM, NPWM). Complete elimination of these distortions usually requires excessive oversampling of the source PCM audio signal, which results to impractical realizations of digital PWM systems. In this paper, a description of digital PWM distortion generation mechanism is given and a novel principle for their minimization is proposed, based on a process having some similarity to the dithering principle employed in multibit signal quantization. This conditioning signal is termed “jither” and it can be applied either in the PCM amplitude or the PWM time domain. It is shown that the proposed method achieves significant decrement of the harmonic distortions, rendering digital PWM performance equivalent to that of source PCM audio, for mild oversampling (e.g., ×4) resulting to typical PWM clock rates of 90 MHz.

Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2007, Article ID 94386, 12 pages doi:10.1155/2007/94386 ... Distortion-Free 1-Bit PWM Coding for Digital Audio Signals ... 1 Department of Computer Science, Ionian University, Plateia ...

Using analytic PCM-to-PWM mapping, combined with a novel method for eliminating PWM-induced distortions (Jithering), a distortion-free, all-digital and high-quality PWM coder was developed. High efficiency and performance is achieved at switching frequencies ...

Using a novel PCM to PWM analytic mapper, the effects of input signal parameters on the PWM-generated distortions are studied and their audibility is assessed using perceptual criteria (NMR and PAQM). A wide range of input signal parameters is studied (e.g. oversampling 2<R<64, quantisation N=4, 8, 16 and 24) and the tests cover both tone-like and typical audio input signals.