AES Tokyo Convention 2009
Paper Session A1

Nowadays, regulation of B type and A type wireless microphone was standardized, most of wireless mike are in the direction of digital format type.Because the demand for good and high sound quality efficient in frequency-use multichannel wireless mike is large in the hall and the theater and other various places, so the development and supplement for new digital microphone system and also reasonable price product is expected to be introduced.

Authors have already reported the principle and the feasibility of synchronous averaging method in the frequency domain which can acquire good response characteristics with a high S/N ratio in an asynchronous sound system between the sides of sound source and measurement. This report proposes a TSP (Time Stretched Pulse) method for practical use, in that a precise impulse response could be obtained without distortion even if the clock frequency of measured sound differs from that of the sound source, and also introduces some applications of this method.

Soundcards can be clocked with a set of fixed sample frequencies. The reference for these frequencies is generated by the card's internal quartz, which feeds an attached PLL (phase locked loop). The PLL output's quare signal refers to the term wordclock, which triggers the respective conversion processes. Two soundcards, however, inherently suffer from a slight wordclock drift. This can be eliminated by feeding one card's external wordclock input with the other card's clock. Since it is due to numerous reasons not possible to transmit the clock in wide area networks (WAN), exact synchronization requires a direct cable connection. Hence, this paper investigates a new solution, which provides precise remote soundcard synchronization via a novel frequency comparison and adjustment method.

Automatic testing at the end of the assembling line is performed to find loudspeaker defects. Distortion measurements can reveal symptoms of driver nonlinearities but they are difficult to interpret and it is hardly possible to distinguish nonlinearities of the electro-dynamical motor from nonlinearities in the mechanical suspension. A fast measurement procedure is presented which assesses the large signal performance of the driver and quantifies the dominant loudspeaker nonlinearities in terms of easy to interpret single-valued parameters like the voice coil offset. These parameters can even be determined when the driver is already mounted in a vented-box system. The direct correspondence to production process parameters allow an optimized controlling of the production process.