v3.0, 20040326, ME
Session O Monday, May 10 15:30 h–18:00 h
MICROPHONES
Chair: Jürgen Wahl, Sennheiser/Neumann, Van Nuys, CA, USA
O-1 An Improved Method of Noise Cancellation—David Herman1, Dudley Haestler1, Simon Busbridge2
1 AudioGravity Ltd., Hove, UK;
2 University of Brighton, Brighton, East Sussex, UK
The effectiveness of conventional noise cancellation techniques is limited by tolerances between the signal and noise channels. A system is described in which the ambient noise error signal is fed back for further cancellation (Advanced Ambient Noise Rejection Technology, ANRT). Small physically displaced microphones differentiate near- field signals from high-level ambient noise. Band limiting filters further reduce high-frequency phase distortion. The effectiveness is increased such that an unintelligible signal produced by normal speech can result in an SNR improvement of 40 dB in an ambient noise field of 98 dBA. The technology can be integrated into a single, small, low-power CMOS analog integrated circuit; it is also ideally suited for MEMS (Si-Mic).
O-2 Close-Talking Autodirective Dual Microphone—Alexander Goldin, Alango Ltd., Haifa, Israel
The paper presents close-talking mode of Autodirective Dual Microphone (ADM) technology developed by Alango Ltd. ADM is an adaptive beamforming technology having two operational modes. In far-talk mode ADM provides optimal directivity for every frequency region such that sounds coming from the back plane are cancelled. In close talk mode all sounds originating outside a close proximity to the microphone are (theoretically) completely cancelled. ADM fast adaptation time leads to excellent noise cancellation in changing noisy environments. ADM technology has a low demand for placing, matching, and distance between individual sensors. This simplifies its integration into mobile and other devices. ADM operational mode is defined by DSP algorithm, easily switching according to situation.
O-3 About a Digital RF-Condenser Microphone—Roland Müller; Peter Holstein, SINUS Messtechnik GmbH, Leipzig, Germany
Digital microphones are commonly based on an LF-condenser with an ADC in the same housing. However, this concept has some disadvantages, such as the inherent problems of LF-condenser microphones with respect to the influence of humidity on sensitivity, distortion, and low cut-off frequency. Therefore, another approach for digital microphones is proposed, whereby the capacity of the microphone capsule controls the frequency of an LC-type generator. The resulting nonlinear distortion is of second order and similar to those of classical microphones with vacuum tube preamplifiers. A negative capacitance can be added to reduce the distortion. There are several ways to implement demodulation and digitalization; simulations show that a sufficient dynamic range can be achieved by using a special kind of delta-sigma-FM-discriminator.
O-4 Fiber-Coupled Optical Microphones—Peter Schreiber1, Sergey Kudaev1, Vladimir Gorelik, Jürgen Peissig2
1 Fraunhofer Institute for Applied Optics and Precision Engineering, Jena, Germany
2 Sennheiser Electronic GmbH & Co. KG, Wedemark, Germany
Motivated by the advantages of optical sensors, like immunity with respect to EMI/RFI and electrically isolated realization, today’s fiber- and micro-optics technology enables the manufacturing of sensitive optical microphones. In the first part of this paper a short review of applicable sensing principles is given and pros and cons for realization are discussed. In the second part, design, manufacturing, and characterization for different fiber-coupled optical microphones employing optical sampling of a membrane are presented.
O-5 Modern Acoustic and Electronic Design of Studio Condenser Microphones—Stephan Peus, Georg Neumann GmbH, Berlin, Germany
Condenser microphones have been used for more than 70 years in professional audio recording applications due to their good frequency response, extended frequency range, and wide dynamic range. The basic design of studio microphone capsules today dates back several decades. Some capsules have been in production unchanged for 50 years or more. Nevertheless, the technical performance of microphones has been improved step by step by continued refinement of the associated electronic circuitry (e.g., tubes versus semiconductors, FET technology improvements, circuitry design aspects, etc.). Not until a few years ago did the quality of the electronics finally match that of the capsule in terms of self-noise level and dynamic range. However, the capsule design has also been improved by making use of technological advances and modern materials. Studio microphones developed recently for high-resolution applications are capable of sensitivity corresponding to the noise level of air particles hitting the diaphragm surface due to thermal molecular movement, and at the same time have a dynamic range of 130 dB or more. This is true for both microphones using analog electronics and microphones using the most recent ADC technology. This paper gives an overview of recent advances in the acoustic and electronic design of studio condenser microphones.
