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IP FOCUS – AUDIO

September/October 2017

AT HOME PRODUCTION STUDIO M4-IP USB BLADE

M4-IP USB BLADE

HD-SDI BLADE

VIDEO

INTERCOM/IFB

VIDEO

MADI BLADE

M4-IP USB BLADE SWITCH

SWITCH GIBRALTAR IP MIX ENGINE

SDI ANALOG ETHERNET IFB (0 LATENCY) M4-IP USB BLADE

M4-IP USB BLADE

IP AUDIO CONSOLE

FIBER WIRELESS MICS

When IP isn’t enough Wheatstone’s VP of technology Andy Calvanese and sales engineer Lon Neumann delve into the possibilities – and challenges – of audio networking in the IP realm

W

e talk a great deal about IP and audio and video, but IP wasn’t originally intended as a real time audio/video delivery medium. IP can bring tremendous adaptability and extensibility to the main or home studio for all kinds of purposes. But you will still need a way to bring audio into the network, manage it to minimise packet dropouts and other quality issues, plus do all those things you normally do with audio. You need something that talks both IP and audio, and preferably knows AES67. That’s where today’s IP audio network comes into play. IP AUDIO FOR INGEST A primary role of IP audio networks is to ingest audio from microphones, production automation systems and other sources.

We know of seve eral news studios that are shared d by two orr more e local ne etwo ork affiliiates.. Th hey quick kly allte ernate newscasts from m one to o the other in n a matter of minuttes For example, in the case of WheatNet-IP audio networking, specialised units called M4IP-USB BLADEs are used at remote venues and in studios as an interface between the microphones and the network. This is

essentially a four-channel mic processor with four XLR inputs and an Ethernet output port, with parametric EQ, de-esser and compressors for each channel. Similarly, another IP audio network unit, the HD-SDI BLADE, can ingest audio from video production automation systems, routers, and other professional video sources that use HD-SDI. It dis-embeds multiple audio channels from HD-SDI streams. A MADI I/O unit can be used for exchanging up to 64 bidirectional channels (AES10) of audio between the audio network and any MADIcompatible intercom system, TDM router, ProTools system or DAW. These units are part of a larger IP audio network that can route audio streams so you don’t have to worry about dropped packets or noticeable jitter, which can lead to synchronisation and audio quality issues. IP AUDIO NETWORKING FOR QOS The biggest problem with transporting realtime audio over IP networks has to do with timing and synchronisation. IP network distribution of packets is non-deterministic. Packets are routed based upon the momentby-moment condition of the network traffic and its switches and routers, and not necessarily which packets were created first. While not a significant issue for a very small system, this can be detrimental as the number

of packets goes up and traffic increases, causing packets to get jumbled and delayed. Engineers in different applications long ago realised that some mechanism for recreating the proper packet order in an IP network would be necessary, hence they created additional protocols that add more information to IP packet headers. Among these are RTP (real-time transport protocol) and RTCP (real-time transport control protocol), which together provide sequencing and prioritisation (QoS) to the packets at a small increase in packet overhead.

IP P audio network king makes it practic cal to bring g aud dio in fro om the field to yo our ho ome stu udio o So while all the major IP audio manufacturers use the IP protocol as the basic transport mechanism, they use RTP/RTCP or similar protocols for packet sequence control. With respect to protocols used, most of the popular IP audio systems are similar. However, they differ in the specific packet loading, timing and synchronisation mechanisms within the protocols. RTP provides identification in the packets about their sequence and order, but it has been up to the IP audio manufacturer to extract this information and to recreate the audio data and timing.

TV Tech Global September/October 2017  
TV Tech Global September/October 2017  

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