
AES New York 2007 Paper Session P7
P7  Signal Processing, Part 3
Saturday, October 6, 9:00 am — 11:30 am
Chair: Dana Massie, Audience, Inc.  Mountain View, CA, USA
P71 SigmaDelta Modulators Without Feedback Around the Quantizer?—Stanley Lipshitz, John Vanderkooy, Bernhard Bodmann, University of Waterloo  Waterloo, Ontario, Canada We use a result due to Craven and Gerzon—the “Integer Noise Shaping Theorem”—to show that the internal system dynamics of the class of sigmadelta modulators (or equivalently noise shapers) with integercoefficient FIR errorfeedback filters can be completely understood from the action of simple, linear pre and deemphasis filters surrounding a (possibly nonsubtractively dithered) quantizer. In this mathematically equivalent model, there is no longer any feedback around the quantizer. The major stumbling block, which has previously prevented a complete dynamical analysis of all such systems of order higher than one, is thus removed. The class of integer noise shapers includes, but is not restricted to, the important family of “Pascal” shapers, having all their zeros at dc. Convention Paper 7201 (Purchase now)
P72 The Effect of Different Metrics on the Performance of “Stack” Algorithms for LookAhead Sigma Delta Modulators—Peter Websdell, Jamie Angus, University of Salford  Salford, Greater Manchester, UK Lookahead SigmaDelta modulators look forward k samples before deciding to output a “one” or a “zero.” The Viterbi algorithm is then used to search the trellis of the exponential number of possibilities that such a procedure generates. This paper describes alternative tree based algorithms. Tree based algorithms are simpler to implement because they do not require backtracking to determine the correct output value. They can also be made more efficient using “Stack” algorithms. Both the tree algorithm and the more computationally efficient “Stack” algorithms are described. In particular, the effects of different error metrics on the performance of the “Stack” algorithm are described and the average number of moves required per bit discussed. The performance of the “Stack” algorithm is shown to be better than previously thought. Convention Paper 7202 (Purchase now)
P73 Evaluation of TimeFrequency Analysis Methods and Their Practical Applications—Pascal Brunet, Zachary Rimkunas, Steve Temme, Listen, Inc.  Boston, MA, USA TimeFrequency analysis has been in use for more than 20 years and many different timefrequency distributions have been developed. Four in particular, Short Time Fourier Transform (STFT), Cumulative Spectral Decay (CSD), Wavelet, and WignerVille have gained popularity and firmly established themselves as useful measurement tools. This paper compares these four popular transforms, explains their tradeoffs, and discusses how to apply them to analyzing audio devices. Practical examples of loudspeaker impulse responses, loose particles, and rub & buzz defects are given as well as demonstration of their application to common problems with digital/analog audio devices such as Bluetooth headsets, MP3 players, and VoIP telephones. Convention Paper 7203 (Purchase now)
P74 TimeFrequency Characterization of Loudspeaker Responses Using Wavelet Analysis—Daniele Ponteggia, Audiomatica  Florence, Italy; Mario Di Cola, Audio Labs Systems  Milan, Italy An electroacoustic transducer can be characterized by measuring its impulse response (IR). Usually the collected IR is then transformed by means of the Fourier Transform to get the complex frequency response. IR and complex frequency response form a pair of equivalent views of the same phenomena. An alternative joint timefrequency view of the system response can be achieved using wavelet transform and a colormap display. This work illustrates the implementation of the wavelet transform into a commercial measurement software and presents some practical results on different kinds of electroacoustic systems. Convention Paper 7204 (Purchase now)
P75 Equalization of Loudspeaker Resonances Using SecondOrder Filters Based on Spatially Distributed Impulse Response Measurements—Jakob Dyreby, Sylvain Choisel, Bang & Olufsen A/S  Struer, Denmark A new approach for identifying and equalizing resonances in loudspeakers is presented. The method optimizes the placement of poles and zeros in a secondorder filter by minimization of the frequencydependent decay. Each resonance may be equalized by the obtained secondorder filter. Furthermore, the use of spectral decay gives opportunity for optimizing on multiple measurements simultaneously making it possible to take multiple spatial directions into account. The proposed procedure is compared to direct inversion and minimumphase equalization. It makes it possible to equalize precisely the artifacts responsible for ringing, while being largely unaffected by other phenomena such as diffractions, reflections, and noise. Convention Paper 7205 (Purchase now)
Last Updated: 20070821, mei
