Yamaha ACU16-C, Manual

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CobraNet, ACU16-C & NHB32-C Guide
5
1 CobraNet
CobraNet—the Technical Stuff
W
hat Networks are Supported?
CobraNet runs on industry-standard 100Base-T Ethernet networks (100 Mbps). It does not
support 10Base-T (10 Mbps). CobraNet can be used with standard off-the-shelf 100Base-T
Ethernet networking equipment, including switches, media converters, CAT5 cables, and so
on. 100Base-T Ethernet equipment is readily available and inexpensive.
P
ackets, Bundles & Isochronous Cycles
On an Ethernet network, data is transmitted in small packets . Digital audio data must be pack-
etized before transmission, and unpacketized upon reception.
The CobraNet equivalent of a packet is a bundle . A single bundle may contain data for up to
eight channels of 20-bit/48 kHz digital audio, or seven channels at 24-bit/48 kHz. Each bundle
consists of a preamble, destination address, source address, frame type, audio data, and FCS
(Frame Check Sequence) error checking.
Bundles are transmitted in isochronous cycles, and the cycle duration is 1.33 ms. There are
eight bundles per cycle. Each cycle starts with a beat packet, which is used for synchronization.
The last packet in the cycle can be used to transmit asynchronous serial data. The ACU16-C
and NHB32-C use this for power amp control, MIDI, and AD824 head-amp control.
The NHB32-C can transmit 4 bundles and receive 4 bundles simultaneously (i.e., 32 channels
in, 32 channels out). The ACU16-C can receive 4 bundles (i.e., 32 channels in).
CobraNet has a fixed latency of 5.33 ms (or 256 samples). This is mostly due to digital audio
packetization and unpacketization .
Preamble
Destination
address
Source
address
Frame
type
CH
1
FCS
Bundle
CH
2
CH
3
CH
4
Audio data
CH
5
CH
6
CH
7
CH
8
A bundle
Isochronous cycle (1.33 ms)
Beat
packet
Bundle
#1
Bundle
#2
Bundle
#3
Bundle
#4
Bundle
#5
Bundle
#6
Bundle
#7
Bundle
#8
Async. serial
data packet
An isochronous cycle