The so-called interface refers to a specification standard, a communication protocol in which two systems communicate with each other, and a docking part that different devices have in order to implement communication with other systems or devices.
Analog audio equipment should pay attention to the level matching, impedance matching and consistency of the connection mode (refer to the consistency of balance and imbalance) when connecting. Even if some deviation occurs, the signal will not be greatly distorted. Therefore, the interface between the devices is not specifically mentioned in the analog device. However, in the interconnection system of digital audio equipment, the interface mode is crucial.
The sampling frequency and the number of quantization bits used by the digital device in performing A/D, D/A conversion, and digital signal processing differ from each other. Therefore, the sampling frequency and the number of quantization bits of the interconnection device should be kept consistent, otherwise the transmission is The signal will cause damage or even work. In order to realize the interconnection between digital audio devices of different formats, a unified digital signal input/output format docking, which is a digital audio interface standard, which is commonly observed by everyone, is developed.
The following is a brief introduction to some of the main interface standards.
1. AES/EBU (AES3-1992) interface
The AES/EBU interface standard is a professional digital audio interface standard developed by AudioEngineeringSo-ciety/European BroadcastUnion (Audio Engineering Association/European Broadcasting Union). It is widely used in a large number of civilian products and professional digital audio equipment, such as: CD player, DAT, MD machine, top sampler, large digital mixer, professional digital audio workstation, etc.
The AES/EBU interface standard is basically the same as AES3-1992, International Electrotechnical Commission (IEC) IEC958 (Type 1), CCIRRec.647 and EBUTech3250E. It can serially transmit the multiplexed dual channel through a balanced interface. The digital audio signal uses a balanced driver and receiver similar to the standard for RS422 digital transmission, with an output level of 2 to 7V.
The transmission medium used in the AES/EBU interface is a coaxial cable or a twisted pair cable. The professional interface allows cable lengths from 100 to 300 m. In the case of no equalization, this interface allows a transmission distance of up to 100m; if equalization is added, it can be transmitted further.
The common physical connection media of AES/EBU are:
The channel coding of the AES/EBU interface uses a bi-phase identification code, which is a binary frequency modulation channel code. Regardless of whether the symbol is "1" or "0", there is a level transition at the beginning of each data bit period.
(1) Balanced or differential connection, a three-core mic shielded cable using an XLR (card) connector with an impedance of 110 Ω, a peak-to-peak range of 0.2 V to 5 V, and a jitter of ±20 ns.
(2) Single-ended unbalanced connection, audio coaxial cable using RCA plug.
(3) Optical connection using a fiber optic connector.
2. Standard civil interface (IEC958, type 2)
The standard civilian interface (IEC958, Type 2) is very similar to the professional AES/EBU interface, but it uses a coaxial cable with a characteristic impedance of 75Q for unbalanced electrical connections. This interface is often used in technical specifications for quasi-professional or residential digital audio equipment, such as CD players and DAT machines. Usually the port uses the RCA type player interface (commonly known as the lotus plug).
3. SPDIF-2 interface SONY and PHILIPS SPDIF-2 (SONY/PHILIPSDIgitalInterfaceFormat), which is designed to transmit digital audio information of one channel with the highest quantization accuracy of 20b with each cable. And adopt 7511 coaxial cable and 75Q BNC type interface terminal. The level is TTL compatible (0 ~ 5V) and the audio channel interface terminal is matched with a separate interface terminal for transmitting the word clock signal. There is also a multi-channel electrical interface that complies with the RS422 standard. This interface uses a D-type multi-channel interface terminal, and a single BNC interface terminal is used to transmit the word clock.
The SPDIF-2 interface is mainly used to transmit audio data to the outside by SONY professional digital audio equipment.
4. Multi-channel audio digital interface (MADI)
The Multi-channel Audio Digital Interface (MAD1) is an interconnection standard between multi-channel digital audio equipment based on the dual-channel AES/EBU interface standard. It can serially transmit 56 channels of linearly quantized audio data over a 75Ω coaxial cable or fiber so that one sample per channel can be transmitted during an audio sampling period.
The 75Ω video coaxial cable and BNC interface connector are specified. The peak-to-peak value of the output voltage of the transmitter should be 0.3-0.6V, and the longest coaxial cable length should not exceed 50m. If you use fiber optic cable, it can transmit farther distances.
For example, the Fiber Distributed Data Interface (FDD1) can be used for connections up to 2 km.
5. Other standard interfaces (1) ADAT
Also known as the Alesis multi-channel optical digital interface, it is a digital audio signal format developed by Ale-SIS of the United States, because it was first used in the company's ADAT eight-track machine. This format uses a fiber optic cable to transmit eight channels of digital audio signals.
(2) TDIF
It is a multi-channel digital audio format developed by Tascam Corporation of Japan, which uses a 25-pin serial cable similar to a computer to transmit eight channels of digital audio signals.
(3) R-BUS
It is a new 8-channel digital audio format from Roland, also known as RMDBII. Its jacks and cables are the same as Tascam's TDIF, and it also transmits 8-channel digital audio signals, but it has two new functions: First, the R-BUS port can be powered, so that when connecting some small devices When used on it, these small devices can be used without an external power supply. Second, in addition to digital audio signals, the R-BUS can simultaneously transmit operational control and synchronization signals.
When two devices are connected by the R-BUS port, the other device can be controlled on one device. For example, when Ro-land's VSR-880 multitrack machine is connected to Ro-land's VM series console via R-BUS, the multi-track machine can be directly controlled on the VM series console.
6.1/0 Interface The host computer and peripheral devices are usually not directly connected, and must be implemented through the corresponding I/O interface circuit.
In a computer, an interface refers to a specification in which a peripheral device and a host understand each other's language, data transmission speed, and instruction timing. Interface types are: SCSI, ATA, USB, and IEEE1394.
(1) SCSI
The SCSI interface is an abbreviation of the small computer system interface, which is a parallel interface (Parallel Interface). It consists of an 8-bit data bus, 1-bit parity, and 9 control signal lines. Used in high-end computing environments (workstations, servers, mainframes, and supercomputers), it is connected to a SCSI-connected hard drive via a 50-wire flat cable (SCSI-2 is 68). Up to 8 external units can be connected to the SCSI interface, and each unit can be divided into several sub-units, such as a hard disk. The rate reaches 20Mb/s.
(2)ATA
The ATA interface, also known as IDE, is also a parallel interface for use in low-end computing environments. It adopts 16-bit data parallel transmission mode, and its data transmission rate is above 10Mb/s. It is connected to IDE hard disk drive through a 40-core flat cable.
(3) USB
1USB (UniversalSerialBus) interface: It is a universal serial interface that supports plug and play. When connecting peripheral devices, such as active hard disk, digital camera, etc., it is not necessary to turn off the power of the host, and directly connect the USB cable of the peripheral. The plug is plugged into a USB socket on the chassis to connect the host to the peripherals. Up to 127 peripherals can be connected when the host is cascaded. The distance between the host and the peripherals can be up to 5m.
USB supports data transfer rates of 1.5 to 12 Mb/s, which meets the requirements of low-speed peripherals.
2USBMIDI interface: USB digital audio interface is used on MIDI interface, namely USBMIDI interface. For example: Roland SC-8850 audio source has a USB interface.
3USB digital audio interface: USB digital audio interface refers to the digital audio interface card in the form of USB interface. Such as DIRECT-MIXusb3, 24bA / D conversion, stereo big three-core line IN / OUT, stereo big three-core line IN / OUT, big three-core microphone and guitar input, headphone jack. IN/OUT level adjustment, all input level LED indication, output level LED indication. 44.1kHz sampling frequency, compatible with Mac/PC/laptop.
(4) IEEE1394
1EEE1394 is a serial bus interface developed by Apple Inc. of the United States called FireWire. It is a standard for high-speed digital interfaces that connect peripherals, specifying transmission rates of 100 Mb/s, 200 Mb/s, and 400 Mb/s. It has become the standard configuration for many Apple computers.
Features: Support hot swap, IEEE1394 is a serial interface, the cable consists of 6 lines, there are power lines and two pairs of A and B signal lines. To ensure the transmission rate, the cable length should not exceed 4.5m.
The comparison between USB and IEEE1394 is as follows.
Transmission data rate: IEEE1394 can reach 400Mb/s, can connect high-speed peripherals; USB is 12Mb/s, suitable for low-speed peripheral connections.
Number of node serial connections: IEEE1394 is 63 and USB is 127.
Connection cable length: 4.5m for IEEE1394 and 5m for USB.
Cable structure: There are 2 pairs of twisted pair signal lines and 2 pairs of power lines in IEEE1394, while USB has only 1 pair of signal lines and 1 pair of power lines.
Packet capacity: 1394B for IEEE1394 and 256B for USB.
Bus arbitration function: IEEE1394 all node controller IC, and USB is only the host controller IC.
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