Building a full feature simultaneous interpretation system using off-the-shelf equipment

In this text we describe the way to build a full interpretation system for seminar etc use, using readily available market equipment. Purpose of the document is to give to Movement’s groups that organize international events the capability to build a simultaneous interpretation system in short order, easily and with low cost. For use in larger scale events, such as the Social Forums, different, more specialized solutions can be applied.

Description of a retour-relay interpretation system

Alternative Interpretation System (ALIS) Working group of the Greek Organizing Committee for the 4th European Social Forum

http://www.babels.org/alis

Version 1.02

In this text we describe the way to build a full interpretation system for seminar etc use, using readily available market equipment. Purpose of the document is to give to Movement’s groups that organize international events the capability to build a simultaneous interpretation system in short order, easily and with low cost. For use in larger scale events, such as the Social Forums, different, more specialized solutions can be applied.

Introduction: Basic Concepts.

In this section we briefly present some basic concepts in simultaneous interpretation.

Booth: The interpretation cabin. In each booth there must be at least two interpreters.

Relay interpretation: In the case that the interpreters in a booth do not speak the language of the speaker, they will need to interpret using the interpretation from another booth which they can understand. This is called “relay interpretation”. Every simultaneous interpretation system needs to provide “relay”.

Retour: Retour is the inverse interpretation from a booth. For example, suppose there is a Greek booth. When the speaker speaks English or French, this booth will output the interpretation in Greek. But when the speaker speaks Greek, since it is rare to find interpreters in the English (i.e.) booth that speak Greek, the Greek interpreters must do “retour”, from Greek to English.

System specifications

The system we present is composed of four booths, but it can be scaled to more booths very easily. The equipment in each booth supports two interpreters. It provides retour and relay capability. An important issue in retour it the following: continuing the above example, when Greeks interpret to English, it is good or even necessary, this English interpretation to be output to the English channel, so that the public which listens to English would not be forced to switch channel (to the Greek one). Therefore the problem of retour is in fact, for each booth to be able to select its output channel. This leads us to the need to separate the concept of the channel from that of the booth. In that way we reach a scheme when every booth will listen to an incoming channel selectively (relay), and transmits to an output channel selectively (retour). For the public transmission system many solutions can be used (cables, infra-red), with the easiest being the use of simple FM transmitters and receivers. Transmitters of 1 Watt in power are enough to cover a big conference room. We will not deal with this issue in the present document, but will focus on the system used by the interpreters.

Equipment Required

For a system with four (4) booths, the following equipment is required:

1.Eight (8) selection switches with four (4) or five (5) inputs: Four of them to be used for the relay (RelaySwitch) and four for the retour (RetourSwitch).

2.Four (4) signal distributors 1-to-5 (or 1-to-6 if we need an extra output for recording). These can be simple distributors like those used for TV signal, with RCA plugs.

3.Four monophonic plugs of 2 inputs to 1 output (2-to-1).

4.Eight quadruple cables.

5.Eight microphones, eight (monophonic) headphones.

6.Four mixers or simple pre-amplifiers with input for two microphones.

7.Four FM transmitters.

Assembling the system

In each booth we put one RetourSwitch, one mixer and one RelaySwitch.

The RelayS (Pic 2) will be used by the interpreters to select what they listen. To its output we connect the two headphones (using a 2-to-1 plug). To its 4 inputs we connect one quadruple cable, “RelayCable” (the other end of the cable will be connected to the outputs of the distributors). The RetourSwitch (Pic 3) will be used by the interpreters to select to which channel the will transmit. To its input we connect the output of the mixer, to which we have connected the two microphones. To its 4 outputs we connect a quadruple cable, “RetourCable” (the other end of the cable will be connected to the inputs of the distributors).

In the center among the booths, in a special place, we place the distributors. All the RetourCables and RelayCables that we mentioned above, end in this place. Each distributor corresponds to one channel. We connect the 4 outputs of each distributor to the RelayCables, one output to each different (quadruple) cable (pic 4). The 5th output of the distributor is connected to the FM Transmitter which corresponds to the distributor’s channel. The 6th output (if available) is connected to the recording equipment (PC or other). To the input of each distributor we connect a plug to which we have connected (short-circuited) one of the four cables of each RetourCable (pic 5).

System Operation

The interpreters select which channel they will listen to from the RelaySwitch. With the connections described above, the two interpreters in each booth will necessarily have to listen to the same channel, they cannot listen to a different one. They also select which channel they will transmit to using the RetourSwitch.

The signal travels from the microphone, through the mixer, to the RetourSwitch and from there to the distributor (channel) which we have selected. Each distributor, as we see in Pic 5, accepts input simultaneously from all the RetourSwitches, from each booth. Nevertheless, only one of these inputs is active. (If more than one booths transmit in the same channel, there will need to be arrangement among the interpreters so that one booth steps out).

Each distributor then distributes its signal to all the booths through the RetourCable, as well as to the respective transmitter.

The floor channel (speaker channel)

The system described above is in essence an intercommunication system among the interpreters. We still have to connect the floor signal (speaker signal) to the system.

To connect the floor to the system, we have to add one more distributor. It will take input from the Public Address system (PA) and will distribute it to the booths through the RelayCables, in a way like the one above. In this case, the RelayCables should be fivefold instead of quadruple.

If we have the Relay switches with 5 positions, one of them will correspond to the floor. If the Relay switches have only 4 positions, then we can assume that each cabin will not be able to listen to “its” channel, only the other ones, and we can connect the floor to its channel’s input in the Relay switch. So, for example, cabin 3 will be able to select the 1st channel in the 1st position of the switch, the 2nd channel in position 2, the floor in position 3, and the 4th channel in position 4.

Annex: Quality Issues etc

There are quality issues in all the parameters of the system. We pin-point some of the most important ones that we faced:

1.The volume of the signal in the booths: Since the signal from the RetourSwitch is split to two headphones, it must be strong enough. This volume depends on the mixer located in each booth, since the signal originates there, and from the volume level of the Public Address system as regards the floor signal. We muse make sure that the volume is adequate.

2.Interference from the transmitters to the booth equipment: If unbalanced microphones are used, there is a possibility that we may have major interference from the transmitter and its antenna to the microphone signal. Moreover, there is the chance that there will be interference to the mixer as well. For these reasons it is good to use balanced microphones, and mixers of good quality.

3.Regarding the transmitters, we note that simple (without amplification) PLLs of one (1) Watt power are enough to override even commercial stations, in the confined space of a room.

4.Costs: We give below some indicative costs for the equipment:

Article, Approximate Cost

  1 Watt FM Transmitter (boxed), 120 Euros

  Distributor (for TV, 3x1-to-3x4), 40 Euros

  Switch (boxed), 10 Euros

  Mixer, 60 Euros

  Microphone (Balanced), 14 Euros

AL.I.S. WG

e-mail: alis at babels dot org