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Saturday, October 11 2:00 pm 3:30 pm
Session Z4 Posters: Signal Processing, Part 1

Z4-1 On Peak-Detecting and RMS Feedback and Feedforward CompressorsJonathan Abel, David Berners, Universal Audio, Inc., Santa Cruz, CA, USA
Differential equations governing the behavior of first-order peak-detecting and RMS feedback and feedforward analog compressors are presented. Based on these equations, the relationship between feedback and feedforward compressor behavior is explored and simple, accurate digital emulations are provided. Feedback and feedforward gain reduction trajectories are shown to be equivalent by transforming the feedback gain reduction into a feedforward gain reduction having a level-dependent time constant. This time constant has the effect of slowing down the transition into and out of compression and accounts for much of the difference in compression character between the two architectures.

Z4-2 Return Loss and Digital AudioStephen Lampen, Belden Electronics Division, San Francisco, CA, USA
Digital audio requires cables made to a specific impedance, 110? for twisted pairs and 75? for coaxial cable. But what happens when cables are the wrong impedance or are damaged or otherwise have their impedance altered? Changes in impedance can affect the signal traveling down a cable and makes a portion of the signal reflect back to the source, called 'return loss.' This paper will show how, and when, return loss can occur, how it is measured, and how it affects digital audio systems. A return loss specification is suggested as a possible addition to the AES specifications for both equipment and cable.

Z4-3 A Generalization of the Biquadratic Parametric EqualizerKnud Bank Christensen, TC Electronic A/S, Risskov, Denmark
An efficient implementation of parametric equalizers is a cascade of biquadratic filter sections. Traditionally, a section operates in one of three operating modes offering low-shelf, bell-shaped, or high-shelf families of responses. In either mode, each section offers three user parameters: Boost/cut gain G, corner frequency fc,, and bandwidth/slope Q. This paper describes the derivation and implementation of a new fourth user parameter, Symmetry, producing a smooth transition between the three above-mentioned operating modes while retaining the meaning of the three conventional user parameters. All degrees of freedom in the biquadratic filter blocks are utilized. Therefore an inverse mapping exists, converting arbitrary (e.g., computer generated) biquadratic coefficient sets back into meaningful EQ parameters allowing further human interpretation and adjustment.

Z4-4 A Review of Smart Acoustic Volume Controllers for Consumer ElectronicsSuthikshn Kumar, Larsen & Toubro Infotech Ltd., Bangalore, India
This paper reviews various schemes for smart acoustic volume controllers for consumer electronics such as televisions, stereo systems, telephones, mobile phones, etc. There are several instances of applications of smart volume controllers in consumer electronic devices. In car stereo systems, the volume level automatically dips when the system detects the telephone ringing. The mobile with smart volume controller provides an improved speech quality even in the presence of high background noise levels. The smart volume controller for television will even out any variations in volume levels from one channel to another and program to program, thus delivering an improvement in perceived quality to the consumer. The smart volume controllers can be personalized to suit the individuals hearing requirements. This paper also reviews several soft computing techniques for smart volume control such as fuzzy logic control, neural control, neuro-fuzzy control, etc.

Z4-5 Head Related Transfer Function Refinement Using Directional Weighting FunctionSin-lyul Lee, Lae-Hoon Kim, Koeng-Mo Sung, Seoul National University, Seoul, Korea
The nonindividualized head related transfer function (HRTF) is known to have a few problems, which are referred to the “hole in the middle” phenomenon and “front-back reversals.” To overcome these problems, a HRTF refinement technique was introduced, but unfortunately, this refinement technique causes sudden degradation in sound quality to occur and difficulty in cross-talk cancellation because of notch frequency exaggeration. In this paper an HRTF refinement using directional weighting function has been proposed to solve these problems. This newly proposed technique weights ordinary HRTF according to its direction to amplify frontal sound intensity. As a result, spectral differences in the “cone-of-confusion” region become more pronounced within overall audible frequencies without having to exaggerate notch frequency. Also, by using this function, cross-talk cancellation filter can be made more easily. We have verified through listening tests that the proposed technique is superior to the previous HRTF refinement in terms of both sound localization and sound quality. Therefore, the refinement of HRTF through the use of the directional weighting function can be applied in the virtual reality, 3-D entertainment, and auralization program to require high quality sound.

Z4-6 A Multibit Delta-Sigma DAC with Mismatch Shaping in the Feedback LoopBruce Duewer, John Melanson, Heling Yi, Cirrus Logic, Inc., Austin, TX, USA
A robust new architecture for multibit delta-sigma data converters is presented. The second order mismatch shaping function is moved inside the feedback loop of a high order modulator, replacing the need for dynamic element matching (DEM) after the modulator. The mismatch shaper makes a trade-off between ensemble quantization error and mismatch induced error. Mismatch error in the frequencies of interest is decreased, and the resulting additional quantization error is dealt with by the delta-sigma feedback loop. This approach allows good nontonal noise shaping performance even in the face of severe element mismatch. The modulator reliably collapses to second order to maintain stability if faced with particularly high noise energy. The modulator also has integrated SACD processing.

Z4-7 An Efficient Low-Power Audio Amplifier with Power Supply Rails Tracking the Output by Means of Pulse Width ModulationRobert Peruzzi, Marvin White, Lehigh University, Bethlehem, PA, USA; David Rich, John A. Nestor, Erik Geissenhainer, Matthew Johnston, Lafayette College, Easton, PA, USA
A low-power audio amplifier with pulse width modulated power supply rails that track the output signal is presented. Because of the tracking power supply rails, the voltage drop over the power transistors is kept as low as possible and nearly constant, so that power efficiency remains high for low as well as high output level signals. A very simple digital input pulse width modulation scheme provides four power rails to a fully differential class-AB power amplifier. The simplicity of the circuit makes it an attractive solution for low cost portable audio applications, instead of using a more complex pulse width modulated class-D audio amplifier. An efficiency increase of about 10 percent has been simulated over the same class-AB output stage using fixed DC rails of 3 Volts and 0 Volts, with very little sacrifice in THD. Also presented are results from a 12-Volt, single-ended hardware prototype of the system.

Z4-8 A Unified Approach to Low- and High-Frequency Bandwidth ExtensionRonald Aarts, Philips Research Labs, Eindhoven, The Netherlands; Erik Larsen, University of Illinois at Urbana-Champaign, Urbana, IL, USA; Okke Ouweltjes, Philips Research Labs, Eindhoven, The Netherlands
Extending the bandwidth of an audio signal may be useful at the low or high end of the frequency spectrum, depending on the application. Also, the actual bandwidth extension algorithm may rely entirely on psychoacoustic effects or may create a physical extension of the signal spectrum. We have developed a common framework for all these problems, and from this framework derived algorithms that address diverse applications in audio signal processing for bandwidth extension. Specifically, we describe algorithms for bandwidth extension applied to enhancing reproduction of bandlimited signals (at the low or high end of the frequency spectrum) and for enhancing reproduction over small loudspeakers.

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