Yamaha DME8o-ES Specifications download pdf (Page 3)

2. EtherSound

The beginning

At the turn of the century, three R&D engineers at Digi-

gram studied Ethernet compliant audio distrbiution meth-

ods, with CobraNet as the world standard at that time.

CobraNet has been developed to function in large scale,

complex applications - but the three engineers didn’t have

such a broad application scope in mind - they narrowed

it down to the live sound reinforcement market, requiring

much simpler topologies and protocols. They ended up

with EtherSound version 1.0 - developed to serve one-way

connections from a mixing console to a speaker controller

/ ampliﬁ er setup using only an inexpensive CAT5 cable.

Their new technology was applied in a large scale live

application for the ﬁ rst time in September 2003 by the

sound reinforcement department of Radio France during a

performance of the opera Carmen - driving 16 loudspeaker

stacks located throughout the 80.000 seat arena ‘Stade de

France’ in Paris. Everybody involved was taken by surprise

- Digigram provided a full working system, doing exactly

what was needed for this job - but in a much simpler way.

The protocol

Remember how the engineers from Peak Audio solved the

timing and sync problem - caused by Ethernet latency - in

the Cobranet protocol ? One CobraNet device sends out a

beat packet on a moment the network is quiet - so it can

travel to all other devices with extremely low delay.

Then - after receiving the beat packet at virtually the

same time - all audio devices send their audio - with ev-

ery device waiting for a ﬁ xed amount of time before the

received audio is output. This method provides the time

buffer required to cope with store/forward and queue

delays in the network. That’s CobraNet in a nutshell.

The inventors at Digigram made one genius simpliﬁ ca-

tion - stating simply that the network must be a daisy

chain. In a daisy chain every device has only one source

device to receive data from, and one destination device

to send data to - so the device doesn’t have to study the

MAC address in the Ethernet packet to decide where the

packet must go. This also means that store/forward and

queue delays never ever occur in an EtherSound system.

The EtherSound chips from Digigram are capable of for-

warding an Ethernet packet in just 1,4 microseconds. In

the audio world we start to worry only if a delay grows

above 11 microseconds ( which is half a sample at 48kHz

), so a daisy chain with up to 7 devices is no problem at

all. And as the delay can be calculated exactly - know-

ing the 1,4 microsecond delay of an EtherSound device

- systems with more than 7 devices can be tuned to be in

sync with short digital delays of a few samples.

EtherSound Version 1

EtherSound version 1 packs the 24-bit samples of 64

audio channels in one packet and sends it down the

daisychain with a pace of 48.000 packets per second.

The number of packets is equal to the sampling rate

of 48kHz, so the receiving device can use the packet

stream as a source to get a stable wordclock. All devices

in the daisy chain receive packet after packet, quickly

replacing and/or inserting individual samples in the

packets before sending the packet further on its way - all

in 1,4 microseconds. A device that inserts audio into

the packet stream is called a ‘master’ device, a device

extracting channels from the packet stream is called a

‘slave’ device. At the end of the daisy chain, the last

device, the audio packets are sent to the last connector

with nothing connected to it - these packets end up in

silicon heaven (don’t feel sorry for them - it’s like being

stuck in an elevator with Brigitte Nielsen).

Inside the packets also some control data is transmitted

by the ﬁ rst device in the network to control settings of

all other devices. This ﬁ rst device is always a ‘Master’

device - the ﬁ rst device to input audio channels in the

packet stream.

So all audio is streaming from the devices IN connector

to the OUT connector - this direction is called ‘Down-

stream’. The Ethernet connection also has a connection

ﬂ owing from the last to the ﬁ rst EtherSound device

called ‘Upstream’. This connection is used by the de-

vices to send status information back to the ﬁ rst device.

A computer connected to the ﬁ rst device can control and

monitor all other devices in the daisy chain using Ether-

Sound Monitor software.

Carmen at the Stade de France, Paris

EtherSound 1.0: downstream daisy chain.

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Yamaha DME8o-ES Specifications Page 3

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