Whirlwind ES2 User Manual

99 Ling Road

Rochester NY 14612

www.whirlwindusa.com

A Digital Transformation

Inside Whirlwind’s E SNAKE

(Adapted from an article that originally appeared in LiveSound! International, March 2004.)

by Al Keltz, Whirlwind Technical Support

It’s been said that soon after the mid 1960s (and mostly unheard) performance by the
Beatles at Shea Stadium in New York City, an enterprising sound person moved some of
the audio gear into the audience area, bundled a few microphone cables together, and
voila! The first “snake” was born.

Pro audio folklore aside, in 1975 Whirlwind became the first commercial manufacturer of

snakes with the debut of the Medusa. A lot of
change and evolution has happened in the
nearly 30 years since, and now, digital has
found its way to our world of snakes and
interconnects, with the goal of improving
functionality and performance.

Several factors led us down the digital path. A
digital system employing lightweight CAT-5
or fiber optic cable would provide the

opportunity to fly cable overhead, around
obstacles or trenched below ground. Digital splits could be accomplished with standard
networking hardware, eliminating the need for costly transformers and interconnects.

Audio networks would also allow dynamic routing – more flexible than dedicated point­to-point analog connections. And digital snakes can run much longer distances and are far
less prone to interference and ground loops. Until a few years ago, the cost of developing
the hardware, software – and especially – a protocol to handle multi-channel audio made
developing a digital snake out of the question for any small manufacturer in a niche

market like live sound. However, this changed with the introduction of CobraNet, a real­time, multi-channel digital audio networking protocol.

With this impediment now out of the way, Whirlwind signed on as a CobraNet licensee
in the late 1990s and then went about the business of designing its first digital audio
snake system.

COMMON TRANSPORT STANDARD

The CobraNet protocol involves transporting uncompressed multi-channel digital audio
and control over standard Ethernet hardware, and currently, there are some 40-plus
manufacturers signed up as licensees of this technology. Because licensees conform to
a common standard for transporting digital audio data, the various devices developed by
these manufacturers can communicate with one another, similar to an Ethernet computer
data network. CobraNet facilitates the transport of up to 64 channels in each direction
between two points on a switched 100Mbs full duplex network. (However, actual
network topology can allow for many more channels within the network and using
gigabit hardware dramatically increases channel count.)

Addressing of CobraNet data allows channels to be routed to specific destinations
anywhere on the network or across LANs (local area networks) – it’s not restricted to a
closed point-to-point structure. The routing provided in network switches can allow
CobraNet to be transported on existing networks along with regular Ethernet data. And,
quite notably, this protocol allows employment of standard off-the-shelf Ethernet
hardware that is readily available, and at a relatively low cost.

CobraNet has become the de facto standard and is used extensively in installs, as well as
some live audio applications such as drive snakes. With all of these advantages and
market acceptance, we decided to use CobraNet as the basis for our digital snake, which
we now unveil as the E SNAKE.

The heart of CobraNet is the CM-1 module, which has the capability of handling up to 32
audio channels in each direction between two points. For this reason, it was decided to
configure E SNAKE as a hardware frame and motherboard with a CM-1 module
mounted on the motherboard.

This motherboard contains eight
slots for accepting up to four input
and four output “daughter boards”.
Each daughter board can handle
eight channels of audio, giving
each frame the capability of 32
inputs and 32 outputs when fully
loaded.

Boards currently available include Mic/Line Input (MLI) and Mic/Line Output (MLO).
Future releases are planned for Line Only Input, Transformered Mic Input, AES/EBU I/O
and Voltage Control I/O versions.

MANAGE VARIOUS CONTROLS

A pair of E SNAKE Frames (ESF), connected to each other through an Ethernet switch,
along with the presence of a personal computer (PC) on the network, replaces the
traditional analog snake. The PC is necessary to run E SNAKE Control software that
allows the operator to manage the various controls and operating parameters of the
system.

If splits are desired, they may be easily accomplished by using additional ports on the
Ethernet switch. However, most short run splits, such as providing for a monitor mix, will
probably continue to be accomplished by traditional analog means.

The original concept was to design a point-to-point replacement for the analog snake.
However, it quickly became obvious that any number of individual ESFs (again, E
SNAKE Frames) could be used in any CobraNet system as nodes capable of being a high
performance access point for multiple channels of inputs and outputs, mic or line level.
(More about this a bit later.)

In order to optimize performance, it was necessary to incorporate mic preamplifiers and
remote control into the MLI (input) cards. For this digital snake system to be accepted by
professionals using high-end mixing consoles, the mic preamps would have to be of the
highest quality possible.

Therefore, it was decided that they would be based around a new chip from Analog
Devices that is designed specifically for high-end mic preamp circuits. The same
considerations applied for the A/D (analog to digital) and D/A (digital to analog)
converters - expensive but necessary for optimum performance.

The MLO (output) cards receive CobraNet digital data and convert it back to analog
audio at the same level that was input to the MLI – mic level in means mic level out. This
way, the operator continues to use the mic preamps in the analog console and receives the
same performance, sonic characteristics and “feel” as if using an analog snake.

However, it’s necessary to provide remote gain adjustment in the MLI to optimize input
to the A/D converter. At the same time, it’s also necessary to prevent those adjustments
from upsetting the gain structure at the analog console. This is accomplished by utilizing
a scheme we call “Gain Tracking.”

A VIRTUAL WIRE

The E SNAKE Control application provides A/D converter input gain control by
highlighting a channel (clicking on it) and moving its on-screen fader with the mouse.
However, if adjustments were made without compensation in the corresponding output

channel on the MLO side, the analog audio level presented to the console would change
too. This would require an additional step of re-adjusting the console’s analog input gain.

The E SNAKE “Gain Tracking” function monitors adjustments to the MLI and
automatically compensates at the MLO by changing the output level by the same amount
– but in the opposite direction. The result is that the analog audio level remains constant
making E SNAKE a “virtual wire.”

It’s important to note that this only applies when connecting ESFs to each other. Other
devices on the network that are being sent CobraNet audio by ESFs will experience a
change in level when adjustments are made to input gain.

Utilizing a CobraNet network allows for a system that could contain multiple ESFs. We
realized that the interface needed to be designed to give the operator an overview of the
entire system and also provide full control over each input channel. This led to
development of “Channel Arrays” to display groups of inputs and “Channel Page Tabs”
as a way of organizing the inputs when controlling multiple ESFs.

In this example, the 64 visible channels represent the inputs for a pair of ESFs located on
stage that are providing 32 inputs each to the system. The user has labeled this tab
“Stage” and the ESFs are divided into upper and lower halves labeled “Stage 1” and
“Stage 2.”