MADI
Encyclopedia
Multichannel Audio Digital Interface, MADI or AES10 is an industry-standard electronic communications protocol
that defines the data format and electrical characteristics of an interface carrying multiple channels of digital audio
. The Audio Engineering Society
(AES) standard for MADI was originally documented in AES10-1991, which was updated by AES10-2003. The MADI standard includes a bit-level description and has features in common with the two-channel format of AES3. Serial digital transmission over coaxial cable
or fibre-optic lines of 28, 56, or 64 channels is supported, with sampling rate
s of up to 96 kHz and resolution
of up to 24 bits per channel.
(FDDI) networking technology (ISO 9314), which was popular in the mid-'90s for backbone links between LAN segments. Since MADI is most often transmitted on copper links via 75 ohm coaxial cables, it is more closely related to the FDDI specification for copper-based links, called CDDI.
AES10-2003 recommends using BNC connector
s with coaxial cables (see part 7.1.4) and ST1 connectors with optic fibres (see part 7.2.1). The specifications about fibres can provide a range of up to 2 km.
The basic data rate is 100 Mbit/s of data using 4B5B
encoding
to produce a 125 MHz physical baud rate. This clock is not synchronized to the audio sample rate, and the audio data payload is padded using "JK" sync symbols.
The audio data is almost identical to the AES3 payload, although with more channels. Rather than letters, they are assigned numbers from 0–55 or 0–63. The only difference is that frame synchronization
is provided by sync symbols outside the data itself, rather than an embedded preamble sequence, and the first 4 time slots of each subchannel are encoded as normal data, used for subchannel identification:
Sync symbols may be inserted at any subframe boundary, and must occur at least once per frame (0.45% minimum overhead.)
The 2003 revision specifies different relations between sampling frequency and number of channels. The next list is from the part 5.1 of the AES10-2003 specifications:
Both versions say that higher sampling frequencies may be accommodated (for example, 96 kHz or 192 kHz) by using two or more channels per audio sample on the link.
The latest AES10-2008 standard includes minor clarifications and updates to correspond to the current AES3 standard.
(AES3), ADAT
(Alesis
Digital Audio Tape), TDIF (Tascam
Digital Interface) and S/PDIF
(Sony/Philips Digital Interconnect Format) are: first, support of a greater number of channels per line; and second, the use of coaxial and optical fibre media that enable the transmission of audio signals over 100 meters and up to 3000 meters. Some main providers of interfaces and computer cards for MADI are:
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...
that defines the data format and electrical characteristics of an interface carrying multiple channels of 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...
. The Audio Engineering Society
Audio Engineering Society
Established in 1948, the Audio Engineering Society draws its membership from amongst engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products for audio, and persons working...
(AES) standard for MADI was originally documented in AES10-1991, which was updated by AES10-2003. The MADI standard includes a bit-level description and has features in common with the two-channel format of AES3. Serial digital transmission over coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
or fibre-optic lines of 28, 56, or 64 channels is supported, with sampling rate
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...
s of up to 96 kHz and resolution
Quantization (sound processing)
In signal processing and digital audio, quantization is the process of approximating a continuous range of values by a relatively small set of discrete symbols or integer values...
of up to 24 bits per channel.
Transmission format
MADI links use a transmission format that is similar to the Fiber Distributed Data InterfaceFiber Distributed Data Interface
Fiber Distributed Data Interface provides a 100 Mbit/s optical standard for data transmission in a local area network that can extend in range up to . Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its...
(FDDI) networking technology (ISO 9314), which was popular in the mid-'90s for backbone links between LAN segments. Since MADI is most often transmitted on copper links via 75 ohm coaxial cables, it is more closely related to the FDDI specification for copper-based links, called CDDI.
AES10-2003 recommends using BNC connector
BNC connector
The BNC connector ' is a common type of RF connector used for coaxial cable. It is used with radio, television, and other radio-frequency electronic equipment, test instruments, video signals, and was once a popular computer network connector. BNC connectors are made to match the characteristic...
s with coaxial cables (see part 7.1.4) and ST1 connectors with optic fibres (see part 7.2.1). The specifications about fibres can provide a range of up to 2 km.
The basic data rate is 100 Mbit/s of data using 4B5B
4B5B
In telecommunication, 4B5B is a form of data communications Block Coding. 4B5B maps groups of four bits onto groups of 5 bits, with a minimum density of 1 bits in the output. When NRZI-encoded, the 1 bits provide necessary clock transitions for the receiver. For example, a run of 4 bits such as...
encoding
Line code
In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...
to produce a 125 MHz physical baud rate. This clock is not synchronized to the audio sample rate, and the audio data payload is padded using "JK" sync symbols.
The audio data is almost identical to the AES3 payload, although with more channels. Rather than letters, they are assigned numbers from 0–55 or 0–63. The only difference is that frame synchronization
Frame synchronization
While receiving a stream of framed data, frame synchronization is the process by which incoming frame alignment signals, i.e., distinctive bit sequences , are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission...
is provided by sync symbols outside the data itself, rather than an embedded preamble sequence, and the first 4 time slots of each subchannel are encoded as normal data, used for subchannel identification:
- Bit 0: Set to 1 to mark channel 0, the first channel in each frame.
- Bit 1: Set to 1 to indicate that this channel is active (contains interesting data).
- Bit 2: notA/B channel marker, used to mark left (0) and right (1) channels. Generally, even channels are A and odd channels are B.
- Bit 3: Set to 1 to mark the beginning of a 192-sample data block.
Sync symbols may be inserted at any subframe boundary, and must occur at least once per frame (0.45% minimum overhead.)
Sampling frequency
The original AES10-1991 specification allowed 56 channels at sample rates from 32 to 48 kHz with a tolerance ±12.5%, in part 4.1. It leads to a total range of 28 to 54 kHz. This produced a total of 56×32×54 = 96768 kbit/s, leaving 3.232% of the channel for synchronization marks and transmit clock error.The 2003 revision specifies different relations between sampling frequency and number of channels. The next list is from the part 5.1 of the AES10-2003 specifications:
- 32 kHz to 48 kHz ± 12,5 %, 56 channels;
- 32 kHz to 48 kHz nominal, 64 channels;
- 64 kHz to 96 kHz ± 12,5 %, 28 channels.
Both versions say that higher sampling frequencies may be accommodated (for example, 96 kHz or 192 kHz) by using two or more channels per audio sample on the link.
Improvements
The original specification (AES10-1991) defined the MADI link as a 56 channel transport for the purpose of linking large-format mixing consoles to digital multi-track recording devices. Large broadcast studios adopted it for use routing multi-channel audio throughout their facilities as well. The 2003 revision, called AES10-2003, adds a 64 channel capability as well as support for "double-rate" sampling at 96 kHz by removing vari-speed operation.The latest AES10-2008 standard includes minor clarifications and updates to correspond to the current AES3 standard.
Usage
MADI was developed by AMS Neve, Solid State Logic, Sony and Mitsubishi and is widely used in the audio industry, especially in the professional sector. Its advantages over other audio digital interface protocols and standards such as AES/EBUAES/EBU
AES3 is the standard used for the transport of digital audio signals between professional audio devices. It is also known as AES/EBU and is published by the Audio Engineering Society and as part of IEC 60958. It was developed by the AES and the European Broadcasting Union and first published in...
(AES3), ADAT
ADAT
Alesis Digital Audio Tape or ADAT is a magnetic tape format used for the simultaneous digital recording of eight analog audio or digital audio tracks at once, onto a Super VHS tape that is used by consumer VCRs.- History :...
(Alesis
Alesis
Alesis is a company based in Cumberland, Rhode Island, that designs and markets electronic musical instruments, digital audio processors, audio mixers, digital audio interfaces, recording equipment, drum machines, professional audio and electronic percussion products...
Digital Audio Tape), TDIF (Tascam
TASCAM
TASCAM is the professional audio division of TEAC Corporation, headquartered in Montebello, California. Tascam is credited as the inventor of the Portastudio, the first cassette-based multi-track home studio recorders. Tascam also introduced the first low-cost mass produced multitrack recorders...
Digital Interface) and S/PDIF
S/PDIF
S/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high...
(Sony/Philips Digital Interconnect Format) are: first, support of a greater number of channels per line; and second, the use of coaxial and optical fibre media that enable the transmission of audio signals over 100 meters and up to 3000 meters. Some main providers of interfaces and computer cards for MADI are:
- Allen & HeathAllen & HeathAllen & Heath is a company based in Penryn, Cornwall, England, specialising in the manufacture of audio mixing consoles...
- AMS NeveAMS NeveAMS Neve Ltd was the result of the amalgamation in 1992 of AMS with Neve Electronics.-Background:Neve Electronics was a British manufacturer of mixing consoles that originated in the work of Rupert Neve in the 1960s...
- Avid TechnologyAvid TechnologyAvid Technology, Inc. is an American company specializing in video and audio production technology; specifically, digital non-linear editing systems, management and distribution services. It was created in 1987 and became a publicly traded company in 1993...
- Calrec Audio
- Cobalt Digital
- Deubner Hoffmann Digital
- DiGiCoDiGiCoDiGiCo is a British company, founded in 2002, that manufactures digital mixing consoles targeted for live audio mixing applications.DiGiCo's most current console lineup comprises the SD-Series of consoles, powered by Stealth Digital Processing. Pioneered with their flagship SD7, Stealth Digital...
- DirectOut
- EuphonixEuphonixEuphonix was a professional audio company located in Mountain View, California, United States. Euphonix produced the first successful line of large digitally controlled analog audio mixing consoles in the late 1980s and has since moved on to all-digital systems....
- EvertzEvertzEvertz is the surname of these persons:*Scott Evertz - Vice President for International Affairs*Theodor Evertz - Franco-Flemish composerEvertz Technologies Ltd. is a multimedia development company in Burlington, Ontario....
- FairlightFairlightFairlight is a digital audio company based in Sydney, Australia. In 1979 they created the Fairlight CMI, the first digital audio sampler, quickly used by artists such as Peter Gabriel, Kate Bush, and Jean Michel Jarre. They are now a manufacturer of media solutions tools such as digital audio...
- Harrison Audio ConsolesHarrison Audio ConsolesHarrison Audio Consoles is an international company based in Nashville, Tennessee that manufactures mixing consoles and other audio technologies for the post-production, video production, broadcast, sound reinforcement and music recording industries...
- Harris Corp.
- Innovason
- Klotz DigitalKlotz DigitalKlotz Digital AG is a manufacturer of audio media products based in Munich, Germany.The company is active in the two business segments Public Address and Radio & TV Broadcast....
- Lab X Technologies
- Lawo
- Lynx Studio Technology, Inc.
- Merging Technologies
- Miranda Technologies
- Optocore
- PESA Switching Systems
- RMERMERME Audio is a German company, based in Haimhausen, that designs and builds professional audio hardware, including audio interfaces, analog to digital converters, and digital-to-analog converters. While the majority of their audio interface solutions are PCIbased as well as PCI-Express, they...
- SADiESadieSadie, , a black Labrador Retriever, is a recipient of the Dickin Medal, the animal equivalent of the Victoria Cross. She was awarded for detecting an explosive device outside the United Nations headquarters in Kabul in November 2005, and was awarded by the Princess Alexandra on 6 February 2007...
- Sierra Video Systems
- Solid State LogicSolid State LogicSolid State Logic is a manufacturer of high-end mixing consoles and recording studio hardware headquartered in Begbroke, Oxfordshire, UK.- Company information :...
- Sonic CoreSonic CoreSonic Core is a German developer of digital audio systems, that in 2007 took over some of the assets of Creamware, and continues to support, manufacture & develop the Scope DSP hardware platform and associated software that was originally developed by that company.The company released the Scope...
- SoundcraftSoundcraftSoundcraft is a British manufacturer of mixing consoles and other professional audio equipment. It was founded by sound engineer Phil Dudderidge and electronics designer Graham Blyth in 1973.-History:...
- StuderStuderStuder is a Swiss manufacturer of professional audio equipment, founded in Zurich in 1948 by Willi Studer. It is known primarily for the design and manufacture of analog tape recorders and mixing consoles. Studer also produce other technology solutions, such as telephony management systems and...
- Sydec Audio
- Yamaha Commercial Audio
External links
- Audio Engineering Society standards, in print