AES San Francisco 2008
Poster Session P12
P12 - Amplifiers and Automotive Audio
Friday, October 3, 5:00 pm — 6:30 pm
P12-1 Imperfections and Possible Advances in Analog Summing Amplifier Design
, MMK Instruments - Belgrade, Serbia; Dragan Drincic
, Advanced School for Electrical & Computer Engineering - Belgrade, Serbia; Sasha Jankovic
, OXYGEN-Digital, Parkgate Studio - Sussex, UK
The major requirement in the design of the analog summing amplifier is the quality of the summing bus. The key problem in most common designs is the artifact of summing bus impedance, which cannot be considered as true physical impedance, because it has been generated by negative feedback. The loop gain of the amplifier used will limit the performance at higher audio frequencies where the loop gain is lower, increasing the channels cross talk. The inevitable effect of heavy feedback is the increased susceptibility of the amplifier to oscillate as well as sensitivity to RFI. The advanced solution, presented in this paper, could be seen in the usage of the transistor common-base pair (CB-CB) configuration as a summing bus. The CB pair offers inherent low-input impedance, low-noise, very good frequency response, and, very importantly, makes the application of total feedback not necessarily.
Convention Paper 7569 (Purchase now)P12-2 A Switchmode Power Supply Suitable for Audio Power Amplifiers
, Factor One Inc. - Keyport, NJ, USA
Power supplies for audio amplifiers have different requirements than typical commercial power supplies. A tabulation of power supply parameters that affect the audio application is presented and discussed. Different types of audio amplifiers are categorized and shown to have different requirements. Over time new technologies have emerged that affect the implementation of AC to DC converters used in audio amplifiers. A brief history of audio power supply technology is presented. The evolution of the newly proposed interleaved boost with LLC resonant half bridge topology from preceding technologies is shown. The operation of the new topology is explained and its advantages are shown by a simulation of the circuit.
Convention Paper 7570 (Purchase now)P12-3 On the Optimization of Enhanced Cascode
, Consultant - Miami, FL, USA
Twenty years ago enhanced cascode and other circuit topologies based on the same design principles were presented to audio amplifier designers. The circuit was supposed to be incorporated in transconductance gain stages and current sources. Enhanced cascode was used in some commercial products but have not received wide adoption. It was speculated that enhanced cascode has reduced phase margin and at times higher distortion being compared to conventional cascode. Enhanced cascode is analyzed on the basis of distortion and frequency response. It is shown how to make the most of enhanced cascode. Optimized novel circuit topology is presented.
Convention Paper 7571 (Purchase now)P12-4 An Active Load and Test Method for Evaluating the Efficiency of Audio Power Amplifiers
—Harry Dymond, Phil Mellor
, University of Bristol - Bristol, UK
This paper presents the design, implementation, and use of an “active load” for audio power amplifier efficiency testing. The active load can simulate linear complex loads representative of real-world amplifier operation with a load modulus between 4 and 50 ohms inclusive, load phase-angles between -60° and +60° inclusive, and operates from 20 to 20,000 Hz. The active load allows for the development of an automated test procedure for evaluating the efficiency of an audio power amplifier across a range of output voltage amplitudes, load configurations, and output signal frequencies. The results of testing a class-B and a class-D amplifier, each rated at 100 watts into 8 ohms, are presented.
Convention Paper 7572 (Purchase now)P12-5 An Objective Method of Measuring Subjective Click-and-Pop Performance for Audio Amplifiers
—Kymberly Christman (Schmidt)
, Maxim Integrated Products - Sunnyvale, CA, USA
Click-and-pop refers to any “clicks” and “pops” or other unwanted, audio-band transient signals that are reproduced by headphones or loudspeakers when the audio source is turned on or off. Until recently, the industry’s characterization of this undesirable effect has been almost purely subjective. Marketing phrases such as “low pop noise” and “clickless/popless operation” illustrate the subjectivity applied in quantifying click-and-pop performance. This paper presents a method that objectively quantifies this parameter, allowing meaningful, repeatable comparisons to be drawn between different components. Further, results of a subjective click-and-pop listening test are presented to provide a baseline for objectionable click-and-pop levels in headphone amplifiers.
Convention Paper 7573 (Purchase now)P12-6 Effective Car Audio System Enabling Individual Signal Processing Operations of Coincident Multiple Audio Sources through Single Digital Audio Interface Line
—Chul-Jae Yoo, In-Sik Ryu
, Hyundai Autonet - South Korea
There are three major audio sources in recent car environments: primary audio (usually music including radio), navigation voice prompt, and hands-free voice. Listening situations in cars include not only listening to a single audio source, but also listening to concurrent multiple audio sources—for example, navigation guided as listening music and
navigation guided or listening music as talking on a hands-free cell phone. In this paper a conventional external amplifier system connected with a head unit by three audio interface
lines was introduced. Then, an effective automotive audio system having single SPDIF interface line that is capable of concurrent processing of the above three kinds of audio sources was proposed. The new system leads to a reduced wire harness in car environments and also increases voice qualities by transmitting voice signals via an SPDIF digital line compared with that via analog lines.
Convention Paper 7574 (Purchase now)P12-7 Digital Equalization of Automotive Sound Systems Employing Spectral Smoothed FIR Filters
—Marco Binelli, Angelo Farina
, University of Parma - Parma, Italy
In this paper we investigate the usage of spectral smoothed FIR filters for equalizing a car audio system. The target is also to build short filters that can be processed on DSP processors with limited computing power. The inversion algorithm is based on the Nelson-Kirkeby method and on independent phase and magnitude smoothing, by means of a continuous phase method as Panzer and Ferekidis showd. The filter is aimed to create a "target" frequency response, not necessarily flat, employing a short number of taps and maintaining good performances everywhere inside the car's cockpit. As shown also by listening tests, smoothness, and the choice of the right frequency response increase the performances of the car audio systems.
Convention Paper 7575 (Purchase now)P12-8 Implementation of a Generic Algorithm on Various Automotive Platforms
—Thomas Esnault, Jean-Michel Raczinski
, Arkamys - Paris, France
This paper describes a methodology to adapt a generic automotive algorithm to various embedded platforms while keeping the same audio rendering. To get over the limitations of the target DSPs, we have developed tools to control the transition from one platform to another including algorithm adaptation and coefficients computing. Objective and subjective validation processes allow us to certify the quality of the adaptation. With this methodology, productivity has been increased in an industrial context.
Convention Paper 7576 (Purchase now)P12-9 Advanced Audio Algorithms for a Real Automotive Digital Audio System
—Stefania Cecchi, Lorenzo Palestini, Paolo Peretti, Emanuele Moretti, Francesco Piazza
, Università Politecnica delle Marche - Ancona, Italy; Ariano Lattanzi, Ferruccio Bettarelli
, Leaff Engineering - Porto Potenza Picena (MC), Italy
In this paper an innovative modular digital audio system for car entertainment is proposed. The system is based on a plug-in-based software (real-time) framework allowing reconfigurability and flexibility. Each plug-in is dedicated to a particular audio task such as equalization and crossover filtering, implementing innovative algorithms. The system has been tested on a real car environment, with a hardware platform comprising professional audio equipments, running on a PC. Informal listening tests have been performed to validate the overall audio quality, and satisfactory results were obtained.
Convention Paper 7577 (Purchase now)