Cobranet
Encyclopedia
CobraNet is a combination of software, hardware and network protocols
designed to deliver uncompressed, multi-channel, low-latency
digital audio
over a standard Ethernet
network. Developed in the 1990s, CobraNet is widely regarded as the first commercially successful implementation of audio over Ethernet
.
CobraNet was designed for and is primarily used in large commercial audio installations such as convention centers, stadiums, airports, theme parks and concert halls. It is most useful in applications where a large number of audio channels must be transmitted over long distances or to multiple locations.
CobraNet is an attractive alternative to analog
audio
, which suffers from signal degradation over long cable runs due to electromagnetic interference
, high-frequency attenuation
, and voltage drop
. Additionally, the use of digital multiplexing
allows audio to be transmitted using much less cabling than analog audio.
-based Peak Audio. Initial demonstrations were of a 10 Mbit/s point-to-point system with limited channel capacity. The first permanent installation of CobraNet in this early form was to provide background music throughout the Animal Kingdom
theme park. The first commercial use of CobraNet as an interoperable standard was during the half-time show at Super Bowl XXXI
in 1997.
CobraNet was first introduced as an interoperable standard in collaboration with manufacturer QSC Audio Products
. QSC was the first to license the technology from Peak Audio and marketed it under the RAVE brand. At this point CobraNet had graduated to Fast Ethernet
and used a patented collision avoidance technique to carry up to 64 channels per Ethernet collision domain
.
CobraNet was subsequently enhanced to support and eventually require a switched Ethernet
network. An SNMP
agent was added for remote control and monitoring. Support for higher sample rates
, increased bit resolutions and lowered latency capabilities were later introduced in an incremental and backwards-compatible manner.
In May 2001, Cirrus Logic
announced that it had acquired the assets of Peak Audio. Leveraging Cirrus DSP technology, a low-cost SoC
implementation of CobraNet was developed and marketed. CobraNet has been widely licensed by commercial audio equipment manufacturers and installed in thousands of facilities worldwide.
CobraNet is transmitted using standard Ethernet packets. Instead of using TCP/IP packets, CobraNet transfers data using data link layer
packets, which travel quickly through hubs
, bridges
and switches
, and are not as susceptible to the latency and QoS
problems commonly found in streaming
protocols using a higher transport layer
. However, since CobraNet does not use an IP protocol
, its packets cannot travel through routers, and therefore it is limited to use on a LAN
; CobraNet cannot be used over the Internet
. The network over which CobraNet is transmitted must be able to operate at a minimum of (also known as Fast Ethernet
). All CobraNet packets are identified with a unique Ethernet protocol identifier
(0x8819) assigned to Cirrus Logic.
While CobraNet has been shown to function properly over wireless network
s under ideal conditions, bandwidth and reliability issues associated with typical 802.11 wireless networks tend to cause frequent dropouts and fatal errors. However, wireless communication of CobraNet data can be reliably accomplished using lasers.
, 20-bit
audio, for a total capacity of 64 channels. CobraNet is somewhat scalable, in that channel capacity increases when 16-bit audio is used, and channel capacity decreases when 24-bit audio is used. The number of channels allowed per bundle is limited by the 1,500-byte Ethernet MTU
.
There are three types of bundles: multicast, unicast, and private:
As long as multicast bundles are used sparingly, it is virtually impossible to exceed the bandwidth of a 100 Mbit network with CobraNet data. However, there are limitations to the maximum number of bundles that can be sent on a network, since the conductor must include data in its beat packets for every bundle on the network, and the beat packet is limited to 1,500 bytes. If each device is transmitting one bundle, there may be up to 184 transmitters active simultaneously (for a total of 184 bundles). If each device is transmitting four bundles, then only 105 transmitters can be active, although they would be producing a total of 421 active bundles. The use of private bundles does not require any additional data in the beat packet, so these network limitations can be sidestepped by using private bundles.
conversion (typically 10–50 samples). Latency can be reduced by sending smaller packets more often. In most cases, the programmer can choose the desired CobraNet latency for a particular CobraNet device . However, reducing audio latency has consequences:
It may seem from the table above that more information can be sent at a lower latency. However, that is not the case. More channels can be sent per bundle, but fewer bundles can be processed simultaneously by one device. So, while eight 24-bit, 96 kHz channels can be sent in one bundle at ms latency, due to processing constraints, the CobraNet device may only be able to send and receive one bundle instead of the usual four. The bundle capacity of CobraNet devices are unique to the particular device, and are not always the same. However, below is a table illustrating the bundle capacity for a Biamp
AudiaFLEX-CM DSP device. The Rx and Tx columns indicate the absolute maximum number of channels that can be received or transmitted. The Rx/Tx column represents the maximum number of channels that can be received and transmitted simultaneously.
The typical CobraNet network cards provided by Cirrus Logic are the CM-1 and the CM-2:
Both cards are designed to be added to audio products by the manufacturer.
which converts a CobraNet signal to eight analog audio signals would require little or no configuration by the end user (apart from possibly selecting the bundle number). If configuration is required (for example, in a DSP box with integrated CobraNet I/O), then the manufacturer of the device typically supplies proprietary software for that purpose.
. These devices typically receive audio from CobraNet (and often from other digital or analog sources simultaneously), process the audio using digital filters and effects (for example, volume control, EQ
, compression
, delay
, crossovers
, etc.) and then output the audio via CobraNet (or other digital or analog outputs). Some DSPs even have an integral telephone hybrid
, and can incorporate CobraNet and other sources into a teleconferencing application.
s with integrated CobraNet help keep the signal chain digital for a longer span. Amplifiers with CobraNet inputs often also have limited DSP and monitoring capabilities built-in.
s with integrated CobraNet help keep the signal chain digital for an even longer span. In a typical unpowered speaker application, the amplifier would be housed far away from the speaker, and a long speaker cable (analog) would be run between the speaker and the amplifier. The speaker cable would be subject to interference and signal loss from electrical resistance. However, a powered speaker
, powered by an electrical cable and fitted with integrated CobraNet inputs, eliminates the speaker cable and replaces it with a network cable. Since a speaker will only use one audio channel out of the bundle, many speakers with CobraNet will also have a number of analog outputs for the rest of the channels in the bundle, which is useful in speaker cluster applications.
s are available with optional CobraNet interfaces for increased channel capacity and reduced cabling.
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
designed to deliver uncompressed, multi-channel, low-latency
Latency (audio)
Latency refers to a short period of delay between when an audio signal enters and when it emerges from a system...
digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
over a standard Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
network. Developed in the 1990s, CobraNet is widely regarded as the first commercially successful implementation of audio over Ethernet
Audio over Ethernet
In audio engineering and broadcast engineering, Audio over Ethernet is the use of an Ethernet-based network to distribute real-time digital audio....
.
CobraNet was designed for and is primarily used in large commercial audio installations such as convention centers, stadiums, airports, theme parks and concert halls. It is most useful in applications where a large number of audio channels must be transmitted over long distances or to multiple locations.
CobraNet is an attractive alternative to analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
audio
Line level
Line level is a term used to denote the strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players....
, which suffers from signal degradation over long cable runs due to electromagnetic interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
, high-frequency attenuation
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
, and voltage drop
Voltage drop
Voltage drop is the reduction in voltage in the passive elements of an electrical circuit. Voltage drops across conductors, contacts, connectors and source internal resistances are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical and electronic...
. Additionally, the use of digital multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
allows audio to be transmitted using much less cabling than analog audio.
History
CobraNet was developed in 1996 by Boulder, ColoradoBoulder, Colorado
Boulder is the county seat and most populous city of Boulder County and the 11th most populous city in the U.S. state of Colorado. Boulder is located at the base of the foothills of the Rocky Mountains at an elevation of...
-based Peak Audio. Initial demonstrations were of a 10 Mbit/s point-to-point system with limited channel capacity. The first permanent installation of CobraNet in this early form was to provide background music throughout the Animal Kingdom
Disney's Animal Kingdom
Disney's Animal Kingdom is an animal theme park located at the Walt Disney World Resort. The fourth park built at the resort, it opened on April 22, 1998, and it is the largest single Disney theme park in the world, covering more than . It is also the first Disney theme park to be themed entirely...
theme park. The first commercial use of CobraNet as an interoperable standard was during the half-time show at Super Bowl XXXI
Super Bowl XXXI
Super Bowl XXXI was an American football game played on January 26, 1997, at the Louisiana Superdome in New Orleans, Louisiana to decide the National Football League champion following the 1996 regular season. The National Football Conference champion Green Bay Packers defeated the American...
in 1997.
CobraNet was first introduced as an interoperable standard in collaboration with manufacturer QSC Audio Products
QSC Audio Products
QSC Audio Products, LLC is an American manufacturer of professional audio products. QSC's target markets are audio professionals in concert, installation, portable entertainment and cinema applications.-History:...
. QSC was the first to license the technology from Peak Audio and marketed it under the RAVE brand. At this point CobraNet had graduated to Fast Ethernet
Fast Ethernet
In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the fast Ethernet standards 100BASE-TX is by far the most common and is supported by the...
and used a patented collision avoidance technique to carry up to 64 channels per Ethernet collision domain
Collision domain
A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...
.
CobraNet was subsequently enhanced to support and eventually require a switched Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
network. An SNMP
Simple Network Management Protocol
Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
agent was added for remote control and monitoring. Support for higher sample rates
Sampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...
, increased bit resolutions and lowered latency capabilities were later introduced in an incremental and backwards-compatible manner.
In May 2001, Cirrus Logic
Cirrus Logic
Cirrus Logic is a fabless semiconductor supplier specializing in analog, mixed-signal, and audio DSP integrated circuits . They are presently headquartered in Austin, Texas. Their audio processors and audio converters are found in many professional audio and consumer entertainment products,...
announced that it had acquired the assets of Peak Audio. Leveraging Cirrus DSP technology, a low-cost SoC
System-on-a-chip
A system on a chip or system on chip is an integrated circuit that integrates all components of a computer or other electronic system into a single chip. It may contain digital, analog, mixed-signal, and often radio-frequency functions—all on a single chip substrate...
implementation of CobraNet was developed and marketed. CobraNet has been widely licensed by commercial audio equipment manufacturers and installed in thousands of facilities worldwide.
Advantages
- Cabling cost – using CobraNet and fast Ethernet, 64 channels of uncompressed digital audio are carried through a single, inexpensive Cat-5Category 5 cableCategory 5 cable is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors...
cable. In the analog world, this would have required 64 separate analog audio cables, each of which cost the same or more than the Cat-5 cable. Using gigabit and/or fiber optic Ethernet variants, the cost of cabling per audio channel is further reduced compared to the fast Ethernet connections. Also, since CobraNet data can coexist with data traffic over existing Ethernet networks, a single network infrastructure can economically serve both audio distribution and other networking needs for a facility. - Flexibility – a well-designed network provides enhanced flexibility for future changes to the system. For instance, audio routing can be changed on the fly with network commands, and do not require any rewiring.
- Reliability – use of Ethernet by CobraNet affords many High AvailabilityHigh availabilityHigh availability is a system design approach and associated service implementation that ensures a prearranged level of operational performance will be met during a contractual measurement period....
features such as Spanning Tree ProtocolSpanning tree protocolThe Spanning Tree Protocol is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and ensuing broadcast radiation...
, Link AggregationLink aggregationLink aggregation or trunking or link bundling or Ethernet/network/NIC bonding or NIC teaming are computer networking umbrella terms to describe various methods of combining multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide...
and Network ManagementNetwork managementNetwork management refers to the activities, methods, procedures, and tools that pertain to the operation, administration, maintenance, and provisioning of networked systems....
. For critical applications, CobraNet devices can be wired with a redundant link. In the case that one CobraNet device, cable, or Ethernet switch fails, the other takes over almost immediately. - Audio quality – audio is transmitted in digitalDigitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
form, and therefore it enjoys the same benefits that any other digital medium does. These benefits include reduced susceptibility to electromagnetic interferenceElectromagnetic interferenceElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
, crosstalkCrosstalk (electronics)In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel...
, coloration and attenuationAttenuationIn physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
due to cable impedanceCable theoryClassical cable theory uses mathematical models to calculate the flow of electric current along passive neuronal fibers particularly dendrites that receive synaptic inputs at different sites and times...
.
Disadvantages
- Latency – delays over the CobraNet transmission medium itself are at least millisecondsCobraNet supports three latency modes: , and ms. See #Latency for details. per network traversal. For some applications, these delays can be unacceptable especially when combined with further delays resulting from propagation timeSpeed of soundThe speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
, digital signal processingDigital signal processingDigital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
and the conversions between analogDigital-to-analog converterIn electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
and digitalAnalog-to-digital converterAn analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
. - Hardware cost – although significant money is usually saved in cabling, at least part of that money is spent on the required CobraNet devices which encode and decode the CobraNet signal.
Transmission
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
packets, which travel quickly through hubs
Ethernet hub
An Ethernet hub, active hub, network hub, repeater hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. A hub works at the physical layer of the OSI model. The device is a form of multiport repeater...
, bridges
Bridging (networking)
Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on flooding and examination of source addresses in received packet headers to locate unknown...
and switches
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
, and are not as susceptible to the latency and QoS
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
problems commonly found in streaming
Streaming media
Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
protocols using a higher transport layer
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
. However, since CobraNet does not use an IP protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
, its packets cannot travel through routers, and therefore it is limited to use on a LAN
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
; CobraNet cannot be used over the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. The network over which CobraNet is transmitted must be able to operate at a minimum of (also known as Fast Ethernet
Fast Ethernet
In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the fast Ethernet standards 100BASE-TX is by far the most common and is supported by the...
). All CobraNet packets are identified with a unique Ethernet protocol identifier
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the PayLoad of an Ethernet Frame. This field was first defined by the Ethernet II framing networking standard, and later adapted for the IEEE 802.3 Ethernet networking standard.EtherType...
(0x8819) assigned to Cirrus Logic.
While CobraNet has been shown to function properly over wireless network
Wireless network
Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise installations avoid the costly process of introducing cables into a building, or as a connection between various equipment...
s under ideal conditions, bandwidth and reliability issues associated with typical 802.11 wireless networks tend to cause frequent dropouts and fatal errors. However, wireless communication of CobraNet data can be reliably accomplished using lasers.
Channels and bundles
CobraNet data is organized into channels and bundles. A typical CobraNet signal can contain up to 4 bundles of audio travelling in each direction, for a total of 8 bundles per device. Each bundle houses up to 8 channels of 48 kHzSampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...
, 20-bit
Audio bit depth
In digital audio, bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data...
audio, for a total capacity of 64 channels. CobraNet is somewhat scalable, in that channel capacity increases when 16-bit audio is used, and channel capacity decreases when 24-bit audio is used. The number of channels allowed per bundle is limited by the 1,500-byte Ethernet MTU
Maximum transmission unit
In computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...
.
There are three types of bundles: multicast, unicast, and private:
- Multicast bundles are "broadcast" from one CobraNet device to all other CobraNet devices in the network using Ethernet multicast addressing. Each CobraNet device individually determines if it will use the bundle or discard it. Therefore, multicast bundles are more bandwidth-intensive than other bundle types. Bundle numbers 1–255 are reserved for multicast bundles.
- Unicast bundles are sent from one CobraNet device to any other device or devices configured to receive the bundle number. Unicast bundles are much more efficient because they attempt to travel only to devices which actually want to receive them. Despite their name, unicast bundles may still be sent to multiple devices, either by transmitting multiple copies of the audio data or using multicast addressing. Bundle numbers 256–65279 are reserved for unicast bundles.
- Private bundles may be sent with unicast or multicast addressing. Bundle numbers 65280–65535 are reserved for private bundles. Private bundle numbers are associated with the MAC addressMAC addressA Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
of the device that transmits them. To receive a private bundle, both the bundle number and the MAC address of the transmitter must be specified. Because private bundles are associated with the transmitters there is no limit on the number private bundles.
As long as multicast bundles are used sparingly, it is virtually impossible to exceed the bandwidth of a 100 Mbit network with CobraNet data. However, there are limitations to the maximum number of bundles that can be sent on a network, since the conductor must include data in its beat packets for every bundle on the network, and the beat packet is limited to 1,500 bytes. If each device is transmitting one bundle, there may be up to 184 transmitters active simultaneously (for a total of 184 bundles). If each device is transmitting four bundles, then only 105 transmitters can be active, although they would be producing a total of 421 active bundles. The use of private bundles does not require any additional data in the beat packet, so these network limitations can be sidestepped by using private bundles.
Synchronization
The CobraNet network is synchronized to a single CobraNet device known as the conductor. A conductor priority can be configured to influence selection of the conductor. Among devices with the same conductor priority, the first to establish itself on the network becomes is elected conductor. All other devices are known as performers. In the event that the conductor fails, another CobraNet device will be chosen to become the conductor within milliseconds. CobraNet cannot function without a conductor.Packets
Four main types of packet are used in the transmission and synchronization of CobraNet:- Beat packets – the conductor outputs a beat packet to all other CobraNet devices on the network, at a rate of 750 packets per second. All other CobraNet devices on the network synchronize their audio clock and their data transmissions to the beat packet. The beat packet contains network operating parameters, clock data and transmission permissions for multicast and unicast bundles.
- Audio packets – also known as "Isochronous Data Packets", these packets are sent out by all CobraNet devices after they receive a beat packet. At standard latency settings, one audio packet is sent for each beat packet received, and each audio packet transmits 64 samples of audio data per channel. However, at lower latency settings, audio packets may be sent twice or four times for each beat packet received. Bundles do not share packets; separate packets are sent in sequence for each bundle transmitted from the same device.
- Reservation packets – these packets are transmitted as needed or typically once per second at minimum. Their function is to control bandwidth allocation, initiate connections between CobraNet devices, and monitor the status of CobraNet devices.
- Serial bridge packets – asynchronous serial data may be sent between CobraNet devices on the same network. Many standard asynchronous serial formats are supported, including RS-232RS-232In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
, RS-422, RS-485 and MIDI.
Latency
The buffering of audio data into Ethernet packets typically incurs a delay of 256 samples (or milliseconds). Additional delays are introduced through A-D and D-ADigital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
conversion (typically 10–50 samples). Latency can be reduced by sending smaller packets more often. In most cases, the programmer can choose the desired CobraNet latency for a particular CobraNet device . However, reducing audio latency has consequences:
- Reducing latency requires more processing power.
- Reducing latency places additional demands on network performance, and may not be possible in some network configurations if the forwarding delayPacket transfer delayPacket transfer delay is a concept in packet switching technology.The sum of store-and-forward delay that a packet experiences in each router gives the transfer or queuing delay of that packet across the network...
is too great. - Since reducing latency means sending smaller packets more often, more high resolution (i.e. 96 kHz, 24-bit) audio channels can be sent per bundle without exceeding the 1,500-byte payload limit for Ethernet packets. See the table below for bundle capacity limits:
| Latency | Channels per bundle | |||||
|---|---|---|---|---|---|---|
| 16 bit, 48 kHz | 20 bit, 48 kHz | 24 bit, 48 kHz | 16 bit, 96 kHz | 20 bit, 96 kHz | 24 bit, 96 kHz | |
| ms | 8 | 8 | 7 | 5 | 4 | 3 |
| ms | 8 | 8 | 8 | 8 | 8 | 7 |
| ms | 8 | 8 | 8 | 8 | 8 | 8 |
It may seem from the table above that more information can be sent at a lower latency. However, that is not the case. More channels can be sent per bundle, but fewer bundles can be processed simultaneously by one device. So, while eight 24-bit, 96 kHz channels can be sent in one bundle at ms latency, due to processing constraints, the CobraNet device may only be able to send and receive one bundle instead of the usual four. The bundle capacity of CobraNet devices are unique to the particular device, and are not always the same. However, below is a table illustrating the bundle capacity for a Biamp
Biamp Systems
Biamp Systems is a manufacturer of commercial audio electronics based in Beaverton, Oregon. Founded in 1976, Biamp has a long history of producing analog mixers, equalizers, and amplifiers. Since the early 2000's, their new products have mainly consisted of programmable audio DSP's....
AudiaFLEX-CM DSP device. The Rx and Tx columns indicate the absolute maximum number of channels that can be received or transmitted. The Rx/Tx column represents the maximum number of channels that can be received and transmitted simultaneously.
| Channels per bundle | ms latency | ms latency | ms latency | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Rx | Tx | Rx/Tx | Rx | Tx | Rx/Tx | Rx | Tx | Rx/Tx | |
| 8 | 32 | 32 | 32/32 | 32 | 32 | 32/32 | 32 | 32 | 16/16 |
| 7 | 32 | 32 | 32/32 | 32 | 32 | 29/29 | 28 | 32 | 14/15 |
| 6 | 32 | 32 | 32/32 | 32 | 32 | 29/29 | 24 | 32 | 12/13 |
| 5 | 32 | 32 | 32/32 | 32 | 32 | 25/27 | 21 | 32 | 12/13 |
| 4 | 32 | 32 | 32/32 | 32 | 32 | 24/24 | 20 | 28 | 12/12 |
| 3 | 32 | 32 | 32/32 | 32 | 32 | 20/21 | 15 | 24 | 9/11 |
| 2 | 32 | 32 | 28/29 | 27 | 32 | 16/16 | 12 | 18 | 6/7 |
| 1 | 16 | 16 | 16/16 | 16 | 16 | 9/10 | 7 | 10 | 4/4 |
CobraNet network cards
CobraNet network cards come in several varieties, some of which can support more channels than others. Additionally, CobraNet network cards have two Ethernet ports labelled "primary" and "secondary". Only the primary Ethernet port needs to be connected, but if both ports are connected they become a redundant failsafe. That is, if the primary port loses communication, the secondary port immediately takes over with no packet loss. Careful network design and topology which takes advantage of this feature can provide extremely high reliability in critical applications.The typical CobraNet network cards provided by Cirrus Logic are the CM-1 and the CM-2:
- CM-1 – the standard CobraNet card, provides 32x32 simultaneous I/O channels.
- CM-2 – compact, low-power, lower cost design provides 8 or 16 simultaneous I/O channels.
Both cards are designed to be added to audio products by the manufacturer.
Software
Cirrus Logic provides a software application known as CobraCAD, which assists in the design of the network on which the CobraNet system will run. It helps to identify if there are too many routers between two CobraNet devices, if a certain latency is possible given the network configuration, and other tasks. However, Cirrus Logic does not provide software to manipulate their hardware. In fact, in the simplest of cases, no software is required by the end user. For instance, a simple breakout boxBreakout box
A breakout box is an electrical device, usually housed in a box, in which a compound electrical connector is separated or "broken out" into its component connectors. Compound connectors are used where sufficient space for connections is unavailable...
which converts a CobraNet signal to eight analog audio signals would require little or no configuration by the end user (apart from possibly selecting the bundle number). If configuration is required (for example, in a DSP box with integrated CobraNet I/O), then the manufacturer of the device typically supplies proprietary software for that purpose.
Licensed manufacturers
Manufacturers who wish to integrate CobraNet connectivity into their devices must license the technology from Cirrus Logic. Many audio equipment manufacturers have included CobraNet in their products. Below is a partial list of notable examples, sorted by device type:DSP
One of the most popular and useful devices that integrates CobraNet is the audio DSPDigital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
. These devices typically receive audio from CobraNet (and often from other digital or analog sources simultaneously), process the audio using digital filters and effects (for example, volume control, EQ
Equalization
Equalization, is the process of adjusting the balance between frequency components within an electronic signal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications. The circuit or equipment used...
, compression
Audio level compression
Dynamic range compression, also called DRC or simply compression reduces the volume of loud sounds or amplifies quiet sounds by narrowing or "compressing" an audio signal's dynamic range...
, delay
Delay (audio effect)
Delay is an audio effect which records an input signal to an audio storage medium, and then plays it back after a period of time. The delayed signal may either be played back multiple times, or played back into the recording again, to create the sound of a repeating, decaying echo.-Early delay...
, crossovers
Audio crossover
Audio crossovers are a class of electronic filter used in audio applications. Most individual loudspeaker drivers are incapable of covering the entire audio spectrum from low frequencies to high frequencies with acceptable relative volume and lack of distortion so most hi-fi speaker systems use a...
, etc.) and then output the audio via CobraNet (or other digital or analog outputs). Some DSPs even have an integral telephone hybrid
Telephone hybrid
Telephone hybrids are an essential functional component of the Public Switched Telephone Network . The term also describes the piece of equipment used in broadcast facilities to enable the airing of telephone callers....
, and can incorporate CobraNet and other sources into a teleconferencing application.
Amplifiers
AmplifierAmplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s with integrated CobraNet help keep the signal chain digital for a longer span. Amplifiers with CobraNet inputs often also have limited DSP and monitoring capabilities built-in.
Loudspeakers
LoudspeakerLoudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s with integrated CobraNet help keep the signal chain digital for an even longer span. In a typical unpowered speaker application, the amplifier would be housed far away from the speaker, and a long speaker cable (analog) would be run between the speaker and the amplifier. The speaker cable would be subject to interference and signal loss from electrical resistance. However, a powered speaker
Powered speakers
Powered speakers, also known as self-powered speakers and active speakers, are loudspeakers that have built-in amplifiers. They can be connected directly to a mixing console or other low-level audio signal source without the need for an external amplifier...
, powered by an electrical cable and fitted with integrated CobraNet inputs, eliminates the speaker cable and replaces it with a network cable. Since a speaker will only use one audio channel out of the bundle, many speakers with CobraNet will also have a number of analog outputs for the rest of the channels in the bundle, which is useful in speaker cluster applications.
Mixing consoles
Many digital mixing consoleMixing console
In professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...
s are available with optional CobraNet interfaces for increased channel capacity and reduced cabling.