Network-based multi-channel signal processing using the precision time protocol

A conventional microphone array system uses a conductor to wire from a microphone to an input via an amplifier. While, a wireless transmission for an array system makes the configuration flexible, and it is expected to provide novel applications widely, such as measuring of impulse response in wide area. Not only in acoustic research field but also in research area of remote sensing of body motion and so on, data acquisition with a precise time synchronization is essential. When a signal received at distributed microphone's position is sent over a computer network, the data is packetized and can include some information at receiving point. When a time is included as information at data acquisition position, the time depends on each data acquisition client device. Since it is possible to use network time protocol or precision time protocol, multi-channel signal processing can be achieved with ease. This paper proposes multiple signals transmission system over a computer network with a time code embedding to synchronize those signals. The signal from a client is reconstructed at a server with the time code. Since the time differences between clients affects to performance of the multichannel signal processing, smaller error in time at a client is preferred. This paper discusses how the error in time between channels affects to performance of the distributed microphone array system.