AES London 2010
Paper Session P22

P22 - Microphones, Converters, and Amplifiers

Tuesday, May 25, 09:00 — 12:00 (Room C5)
Chair: Mark Sandler, Queen Mary University of London - London, UK

P22-1 A Comparison of Phase-Shift Self-Oscillating and Carrier-Based PWM Modulation for Embedded Audio Amplifiers—Alexandre Huffenus, Gaël Pillonnet, Nacer Abouchi, Lyon Institute of Nanotechnology - Villeurbanne, France; Frédéric Goutti, STMicroelectronics - Grenoble, France
This paper compares two modulation schemes for Class-d amplifiers: phase-shift self-oscillating (PSSO) and carrier-based pulse width modulation (PWM). Theoretical analysis (modulation, frequency of oscillation, bandwidth, etc.), design procedure, and IC silicon evaluation will be shown for mono and stereo operation (on the same silicon die) on both structures. The design of both architectures will use as many identical building blocks as possible, to provide a fair, “all else being equal,” comparison. THD+N performance and idle consumption went from 0.02% and 5.6mA in PWM to 0.007% and 5.2mA in self-oscillating. Other advantages and drawbacks of the self-oscillating structure will be explained and compared to the classical carrier-based PWM one, with a focus on battery-powered applications.
Convention Paper 8127 (Purchase now)

P22-2 Digital-Input Class-D Audio Amplifier—Hassan Ihs, Christian Dufaza, Primachip SAS - Marseille, France
Not only digital-input class-D audio amplifier directly converts digital PCM-coded audio signal into power, it also exhibits superior performances with respect to traditional PWM analog class-D amplifiers. In the latter, several analog techniques have to be deployed to combat the many side-effects inherent to analog blocks, resulting in complex circuitry. Digital domain provides many degrees of freedom that allow combating signal non-idealities with no or just little extra cost. As the output to the real world is analog, digital class-D amplifier requires Analog to Digital Conversion (ADC) in feedback to compensate for jitter, signal distortions, and power supply noise. With careful sigma delta modulation design and few digital techniques, the class-D loop is stabilized and achieves superior audio performances. The audio signal cascade chain is tremendously simplified resulting in significant reduction in area cost and power consumption. For applications that require analog input processing, the digital class-D still accepts analog inputs with no extra cost.
Convention Paper 8128 (Purchase now)

P22-3 Digital PWM Amplifier Using Nonlinear Feedback and Predistortion—Peter Craven, Algol Applications Ltd. - Steyning, West Sussex, UK; Larry Hand, Intersil/D2Audio - Austin, TX, USA; Brian Attwood, PWM Systems - Crawley, Sussex, UK; Jack Andersen, D2Audio - Austin, TX, USA (deceased)
A nonlinear feedback topology is used to reduce the deviations of a practical PWM output stage from ideal theoretical behavior, the theoretical nonlinearity of the PWM process being corrected using predistortion. As the final output is analog, an ADC is needed if the feedback is to be digital, and several problems arise from the practical limitations of commercially-available ADCs, including delay and addition of ultrasonic noise. We show how these problems can be minimized and illustrate the performance of a digital PWM amplifier in which feedback results in a significant reduction of distortion throughout the audio range.
Convention Paper 8129 (Purchase now)

P22-4 Microphone Choice: Large or Small, Single or Double?—Martin Schneider, Georg Neumann GmbH - Berlin, Germany
How do large and small diaphragm condenser microphones differ? A common misapprehension is that large capsules necessarily become less directional at low frequencies. It is shown that this is not a question of large or small, but rather of single or double diaphragm design. The different behaviors have a direct impact on the sound engineers’ choice and placement of microphone. Likewise, the much debated question of proximity effect with multi-pattern microphones and omnidirectional directivity is discussed.
Convention Paper 8124 (Purchase now)

P22-5 Improvements on a Low-Cost Experimental Tetrahedral Ambisonic Microphone—Dan T. Hemingson, Mark J. Sarisky, University of Texas at Austin - Austin, TX, USA
An earlier paper [Hemingson, Dan & Sarisky; A Practical Comparison of Three Tetrahedral Ambisonic Microphones, 126th AES Convention Munich May09] compared two low-cost tetrahedral ambisonic microphones, an experimental microphone and a Core Sound TetraMic, using a Soundfield MKV or SPS422B as a standard for comparison. This paper examines improvements to the experimental device, including that suggested in the “future work” section of the original paper. Modifications to the capsules and a redesign of the electronics package made significant improvements in the experimental microphone. Recordings were made in natural environments and of live performances, some simultaneously with the Soundfield standard. Of interest is the use of the low-cost surround microphone for student and experimental education.
Convention Paper 8125 (Purchase now)

P22-6 Analysis of the Interaction between Ribbon Motor, Transformer, and Preamplifier and its Application in Ribbon Microphone Design—Julian David, Audio Engineering Associates - Pasadena, CA, USA, University of Applied Sciences Düsseldorf, Düsseldorf, Germany
The transformer in ribbon microphones interacts with the complex impedances of both the ribbon motor and the subsequent preamplifier. This paper presents a test setup that takes the influences of source and load impedances into account for predicting the amplitude and phase response of a specific ribbon microphone design in combination with different transformers. As a result, the effect of the transformer on the amplitude and phase response of the system can be simulated in good approximation by means of a generic low-impedance source. This allows for optimizing the ribbon/transformer/load circuit under laboratory conditions in order to achieve the desired microphone performance.
Convention Paper 8126 (Purchase now)