Audio input switch. Automatic audio switcher

Less common are audio-only switches. This is due to the fact that part of the audio signal switching functions are also performed by such common audio processing devices as mixers, digital mixers, and digital audio platforms. However, despite new technologies and switching functions inherent in mixers, professional installations require audio signal switchers of various types.

The Atanor group of companies represents on the Russian market and offers for use high-quality switches from the following companies:

Kramer (About company )
ATEN (About company )

View our equipment price list. You can download the current price list here:

What are switches used for?

Switches are needed in several cases.

If you have several audio sources and one sound system or audio device to which you want to output the signal from the sources in turn
If you have multiple audio sources and multiple devices or systems to which you want to output signals from the sources
If you have several audio sources and several sound zones in the public address or public address system to which you want to output signals from the sources
Other cases...

Types of Professional Audio Switchers

Audio switches. Types by number of output channels and principle of operation.

Switches allow you to switch any of the input channels to an output channel. If a device has one output channel, it is usually called simply a “switch” (or, audio switch). Such a video switch allows you to switch the audio signal from any of the input channels to the output channel. An audio switch with one output channel can have one or more redundant outputs for connecting a second audio device or system to it. In this case, the same sound signal is sent to all output channels.

A separate case of switching audio signals is a switch with one input channel. In this case, switching of input channels is not required and the switch is essentially a device that distributes and amplifies the input audio signal into the output paths. Such devices are called “distribution amplifiers” of the audio signal.

If an audio switch has two or more output channels with two or more input channels, such a switch is called a “matrix audio switch.” A matrix switcher can switch any of the audio input channels to any of the output channels. The name or description of the matrix audio switcher must include an indication of the number of input and output channels. For example: Kramer VS-88A. 8:8 Balanced Audio Matrix Switcher

Thus, according to the number of output channels and operating principle, video switchers are divided into:

Switches
Matrix switchers
Separately - distribution amplifiers

Kramer distribution amplifiers

Switches. Types by management

If a switch can switch only by mechanically pressing a button located on the panel of the device itself, in this case such a switch is called mechanical. If the switch has a port for supplying control signals, then such a switch is called managed. Switches that support control according to any standard (for example, RS-232) are easily integrated into complex integrated systems. Thus, according to management capabilities, switches are divided into:

Mechanical audio switches
Switches controlled by dry contact closure
Infrared Managed Switches
Switches that support management according to recommended standards (RS-232, RS-485 and others)

Switches. Types according to the switched audio signal standard.

The main types of Kramer switchers according to the switched audio standard are as follows:

Analogue Audio Balanced Mono Switchers
Analogue audio unbalanced mono signal switchers
Analogue unbalanced stereo audio switchers
Analogue balanced stereo audio switchers
Line audio switches
Microphone switches
AES/EBU digital audio switchers
IEC 958 Digital Audio Switches
S/PDIF digital audio switchers
Digital Audio Switches EIAJ CP340/1201

Switch Services

The Athanor group of companies offers the following services for audio signal switches:

Consulting on Kramer and ATEN switches
Selection of switches for various types of projects
Design of public address and public address systems using Kramer and ATEN switches
Design of audio broadcast systems using Kramer and ATEN switchers
Supply of Kramer and ATEN switches
Installation of switching systems and switches Kramer and ATEN
Supervised installation of switching systems and switches Kramer and ATEN
Training in the use and selection of switches as part of training in the design of halls and the implementation of various types of projects
Creation and implementation of centralized automated control systems compatible with switches
Rental of switches (for presentation events, exhibitions, conferences)

To learn more about the professional switching equipment and services offered by the Athanor Group of Companies,

Functionality. The range of brands includes audio switchers that can be used independently or synchronously with video switching devices. Almost all video switchers have a built-in function for switching stereo signals.
Control. The catalog contains simple mechanical equipment that operates without power supply - the contacts are closed using switches. More complex digital models are capable of operating in automatic mode, they can be controlled remotely via the RS232 protocol, and are equipped with software for receiving commands from a computer.
Execution. We offer switches in rack housings (with special fasteners) for ergonomic installation on racks. Compact desktop options are also available; using rack adapters, they can be placed on standard 19" racks.

When choosing, you need to consider the type of incoming signals - there is equipment for receiving audio, VGA, audio and VGA, composite video CV, component video YUV and YPbPr, RGBHV, DVI, HDMI, USB, Ethernet, RS232, 422 and 485. Also consider the number of switched sources. For progressive installation systems, it is optimal to buy multifunctional equipment. For example, the Kramer VS-808xl and VS-804xl matrix switchers can transmit sound independently of the image (audio delay function), set the switching sequence, and store up to 6 presets in memory for quick access to frequently used configurations.

Upon request, we can perform system integration of the installation system - we will develop a project, select the optimal equipment, including switching equipment, install all elements of the kit, and conclude a service agreement.

Let's start with the basic terms.

A switch is a device for closing and stopping the action of electric current, as well as for changing its direction. A matrix is a two-dimensional array of elements of the same type. The position of an element in the matrix is determined by the row number and column number. A matrix switcher is a two-dimensional device with dimensions NxM, which allows you to route signals from N inputs to M outputs.

The switch may be passive or active. In a passive device, only signal switching occurs: contacts are closed or opened. The switching process itself can be mechanized and automated, or it can be manual, which is exactly how the telephone switch was designed a hundred years ago.

An active switch assumes the possibility of some influence on the signal, this could be amplification, regeneration or synchronization, indication and other functions.

Finally, the switch can be a real device, or it can be virtual, when data flows are redirected by software.

The Science of Contacts

Mechanical contact

Historically, mechanical contact was the first - a plug was inserted into the socket. Simplicity and clarity are the advantages of the solution. Such switches are still used today. Even without disassembling the patch panel, it is easy to predict its shortcomings - the service life is short: during operation, the contacting surfaces of the connectors wear out, and the contacts deteriorate. The atmosphere does not have a very positive effect on open surfaces; even coating with noble metals does not help.

Using buttons or toggle switches allows you to separate connectors, cables and connections. As a result, it is possible to optimize each link of the complex for the problem it solves, at least potentially. But all the same, one hundred thousand switchings is a pipe dream for both the connector and the toggle switch.

Both connectors and toggle switches are designed for manual operation. Automating the process or providing remote control of a mechanical switch is not easy.

Nevertheless, both “plug” and “push-button” switches are deservedly popular: simple, understandable and cheap - these are the main properties of this line of equipment.

Mechanical contact with electrical control

An electromechanical relay is quite suitable for solving switching problems. Electrical control eliminates the difficulties of automation and remote control. For protection, contacting surfaces can be placed in an inert atmosphere, in which case performance characteristics are significantly improved. This is exactly how relays are designed with contacts placed in a sealed glass flask, that is, reed switches. One hundred thousand switchings is not the limit for relay-based switches.

Electronic key

The FET channel conducts or does not conduct current depending on the voltage applied to the gate. Theoretically, a matrix of field-effect transistors is an excellent switch: the issue of automation is easily resolved, there are no wearing contacts, and the service life increases by several orders of magnitude. There is also no contact bounce - an eternal problem with mechanical switches.

But the advantages of electronic keys turned out to be so significant that they outweighed the disadvantages.

Basic properties of switches and switches

Analysis of the equivalent circuit shows that as the frequency of the signal increases, the attenuation of the open circuit will decrease. Specific numbers depend on many reasons, primarily on the input resistance of the signal receiver: the higher RIN, the easier the signal penetrates through the capacitance of the open contact.

If the circumstances are unfortunate, the attenuation at the upper limit of the audio frequency range can drop to 60 dB, which is noticeable to the ear. The likelihood of this situation is low because most professional devices have an input impedance of 600 ohms or 10 kohms. Devices with a high-impedance input (the so-called instrument input - 100 kOhm or more) must be connected to a mechanical matrix switcher with caution.

The ohmic insulation resistance (of the order of 10 9 Ohms) of a mechanical relay usually does not manifest itself in any way and can be neglected.

The contact itself can make itself felt. Although its resistance is small (about 0.1 Ohm), it turns out to be dependent, in particular, on the current flowing through the contact and on other destabilizing factors. As a result, as the contacting surfaces wear and their compression force changes, additional noise appears; they can be noticeable in analog audio signal circuits. We must not forget about the nonlinear properties of the contact in the microcurrent mode. (Recently, interest has also increased in the nanocurrent regime - editor's note). Specialized relays are produced that are designed for switching low currents. Calibrated mechanical parameters of the contacting surfaces, their special design and the use of special materials ensure stable operation even at low currents. For such relays, the manufacturer guarantees contact parameters in the current range, for example, from 10 -6 to 0.01 A. Simple relays are designed for switching currents in a much narrower range, usually from 10 -3 A.

Sometimes you have to deal with interference from control circuits: when voltage is applied to the relay coil, a click appears in the signal circuit.

An electronic key has slightly worse electrical characteristics - the resistance of the open key reaches tens of ohms. A current flows through a locked key (about 10 -8 A). To reduce the influence of these parameters on the quality of switching, various circuit solutions are used. An additional switch closes the signal circuit, significantly increasing attenuation: the gain can reach 30...40 dB.

The response speed of electronic keys is high, the entire switching process is completed in a time not exceeding 10 -6 seconds. Mechanical switches do not work so fast: the relay response delay is a few to tens of milliseconds, a manual switch works even slower, we are talking about seconds for the switching process itself. Here we must also add the time that the operator needs to think about the decision, go to the switch and find the required connector or button on it.

Electronic analog signal switches are significantly less protected from interference from control circuits than conventional mechanical relays. Through the joint efforts of chip and switch developers, it was possible to reduce this interference to quite acceptable values, but we do not see this result in all devices - high quality does not come cheap.

A few words about quality

The switch is designed to ensure interaction between signal sources and receivers, including the exclusion of mutual unauthorized influence. That is why, in addition to the switches themselves, the matrix switcher of analog signals may include buffer amplifiers, devices for galvanic isolation and other service “little things”. In this case, the quality of switching is practically independent of the parameters of the signal source and receiver, and transformer isolation radically reduces the mutual influence of devices in the switched complex.

Based on cheap toggle switches or connectors, you can make a matrix switcher with impressive parameters, and measurements will show an excellent picture. The self-noise voltage is literally a few microvolts. The losses in a closed circuit are thousandths of a decibel, the attenuation of an open circuit is well over a hundred decibels. Nonlinear distortions are at the limit of the resolution of the best instruments.

The simplicity of the design and the “short signal path” look tempting, but do not always allow you to get good or at least acceptable sound. Mutual circuit interference, loops and contact phenomena can negate the benefits of this simple and beautiful design. Let's not forget about the operational properties: a mechanical switch will remain mechanical, and it is difficult to automate it. Let me remind you that ease of use is one of the components of the quality of the device.

The parameters of really good switches don't look so nice. Buffer stages introduce distortion, decoupling transformers even more so. As a result, the tables appear with parameters “K g = 0.1%”, “frequency range from 20 Hz to 20 kHz with unevenness of 0.5 dB” that are almost indecent for today’s level of technology. Such devices are bought not for the eyes, but for the ears.

Digital mechanics

A “mechanical” switch with buttons and XLR connectors can be used for more than just analog signal circuits. It can also be used for switching digital signals of the AES/EBU format. Some difference in wave resistance from the nominal value will not entail fatal consequences. The fact is that the physical length of the cables in such a switch is significantly less than the wavelengths and additional losses turn out to be insignificant.

With such mechanical switching, troubles of a completely different nature await us. Disconnecting one AES/EBU digital signal source and connecting another will result in synchronization failure. The sound will be interrupted for a while, long enough to notice the failure. A similar picture occurs in television: when “mechanically” switching sources, the picture breaks down. After a short period of time, frame synchronization is restored and the image is stabilized. The same thing happens when switching an AES/EBU signal - frame synchronization is disrupted with all the ensuing consequences.

To eliminate switching artifacts, special measures are taken to synchronize data flows and master oscillators of the complex devices.

Benefits of switching

There are many options for using switches. In particular, this device is useful in a radio station studio for organizing backups. The signals from the main sources are fed to a matrix switcher, through which the studio output signal is fed to the delivery line.

The question arises: why might this be necessary, since the studio configuration remains constant? Indeed, in general the studio remains unchanged, but there are also specifics. The most advanced remote control does not provide absolute reliability. Power supplies fail, connectors break, wires break, digital systems freeze.

If there is a matrix switcher, by pressing one button, the signal from the output of the on-air computer is sent to the input of the channel, all other equipment is excluded from the path. This configuration of the studio makes it possible to instantly, without interruption in broadcasting, switch to a backup operating system and calmly do, for example, repairing a faulty remote control.

There are other examples of using a matrix switcher in radio broadcasting - ensuring the interaction of several studios. Obeying the will of the production editor, the live broadcast studio becomes a rehearsal room, the second studio switches to live broadcast mode, and the third begins a press conference with video broadcast. To fully use several studios, you will need a large matrix switcher or cascade connection of several “small” ones.

In a complex digital complex, the question arises of organizing data flow management, that is, routing, and not just switching audio signals. This problem is also solved, and the user gets his hands on a complete solution, which includes, in particular, a matrix switcher. But a router can be implemented not only as a hardware device, but also as a computer control application program.

Well, the computer is our future. A little more, and it is the computer, without any human intervention, that will direct the signals itself, removing and inserting connectors - development proceeds in a spiral.

The situation for which this switch was developed was the following: there is a certain room where a sound reproduction system is installed that continuously plays music from a computer (PC), but there is also another signal source - a television (TV), and accordingly, when a sound signal appears at its output , the system should switch to playing TV sound.

As can be seen from scheme, the control for the switch is the signal of the right channel (R), coming from the TV, it is fed to an amplifier made on the basis of an op-amp - U1A. The gain of this stage, necessary for accurate operation of the device, can be adjusted using the trimming resistor RV1. Next, the amplified signal is fed to a voltage rectifier circuit made on elements C2, D1, D2, C3.

The rectified voltage is used to control transistor Q1, in the base circuit of which there is a tuning resistor RV2 connected in parallel with the electrolytic capacitor C3; with this resistor you can adjust the “reverse” switching time, i.e. the time after which the switch will return to PC mode after the control signal disappears. It is necessary to select the optimal “reverse” switching time so that it is not too long - for example, the sound from the TV is no longer received, and there is still no music from the PC, and it is not too short - in this case, the switch can switch to PC mode even for pauses in the TV soundtrack.

From collector Q1, the control signal, to be converted to a “digital” form, is supplied to the input of an inverter with a Schmitt trigger - element U3E. Switch SW1 allows you to select the operating mode of the device - automatic, or manually turning on the TV mode. The basis of the switch is the U2 4053 chip (CD4053, KR1561KP5), which consists of three bidirectional analog switches (only two of them are used - X and Z). Control is carried out via inputs A (11) and C (9) combined together; the enable input for the switches of the microcircuit Inh (6) is connected to a common wire. When working with analog signals, for the 4053 chip, it is necessary to use a negative voltage source - pin VEE (7).

The switch is powered from a simple bipolar source, made according to the following circuit: a 6-0-6V / 500mA network transformer, four FR103 diodes, two 2200uF/16V electrolytic capacitors, integrated stabilizers such as L78L05 and L79L05.

Operational amplifier U1A - LM358M, in SO8 package (only one amplifier is used out of two available in the case); microcircuit U3 - type 74HC14, in SO14 housing (inputs 1, 3, 5, 9 of the unused elements of this microcircuit, you must connect to its output 16 - “+” supply voltage); miniature type 3329H were used as tuning resistors RV1, RV2; all fixed resistors are SMD (0805); electrolytic capacitors C2, C3 - any of suitable dimensions; capacitors C1, C4, C5 are ceramic SMD (1206).

The circuits of the switch and its power supply are mounted on sections of a breadboard, placed in a plastic case of the Gxxx type; the connectors for input and output signals are of the “tulip” type, located on the rear panel of the case. The SW1 switch and the power-on indicator LED are located on the front panel.

This scheme was developed in a relatively short time, using components that were, as they say, “on hand,” so there are some “ugliness” and suboptimalities in it, but nevertheless, the device was made and is being used quite successfully.

Works on the website "Electron55.ru"

The advantages of an audio matrix switcher include:

flexible modular architecture, which allows you to assemble a device “like out of cubes” for the desired task and the available budget;
the presence of many functions and sound processing capabilities, including 15 different filters, equalizers, echo and noise suppressors, limits, AGC, delay, etc.;
complete set of remote control devices and interfaces;
a large number of inputs/outputs for connecting various equipment;
addition of hardware and software for noise suppression, echo, etc.

Among the interfaces in such devices there are microphone and line inputs and outputs, telephone jacks, Ethernet and USB ports, and outputs for amplifiers. In addition, this equipment has ample opportunities for switching and mixing these interfaces with each other, as well as additions in the form of manual and automatic mixers.

Where is an audio matrix switcher used?

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