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What is a Simultaneous Interpreter?

If you’ve ever seen a sign language interpreter at the bottom of your screen during a news segment or presidential debate, you’ve seen a simultaneous interpreter at work. Often hired for large multinational meetings and international conferences, the job of a simultaneous interpreter is to provide real-time interpretation of a target language.

This article will provide a comprehensive understanding of simultaneous interpreting – its significance, benefits, challenges, and applications, as well as what to consider when planning an event requiring simultaneous interpretation.

Interpreters vs. Translators

Before we get into the nitty-gritty of simultaneous interpreting, let’s take a moment to clarify some terminology. Though the terms are often used interchangeably, the jobs of an interpreter versus a translator are quite different. A translator works with written language, taking anything from legal documents to books, articles, websites, transcripts, or subtitles written in one language and rendering them in another. An interpreter, on the other hand, works with spoken language (or sign language), acting as a language conduit for two or more people interacting across language barriers.

What is the Difference between Consecutive and Simultaneous Interpreter?

There are two major kinds of interpreting: simultaneous and consecutive. In consecutive interpreting, which is the most common form of interpreting, a speaker says a few sentences and then pauses while the interpreter translates. This type of interpreting is best suited to one-on-one meetings or small group gatherings, such as parent-teacher conferences or doctor’s appointments.

In contrast, simultaneous interpretation is most often used during events that are less conversational in nature, such as presentations or conferences, or when a multilingual audience requires interpretation into a variety of languages.

Simultaneous interpretation requires the interpreter to listen and interpret the target language at the same time. This takes a great deal of skill and can be extremely cognitively taxing. To get a sense of how challenging simultaneous interpreting is, try listening to the radio and parroting back what the host or speaker is saying in real-time without losing the thread. Now imagine doing that with the added challenge of translating what’s being said into another language.

A note on whispered interpreting

Typically, a simultaneous interpreter broadcasts their interpretation to event attendees wearing headphones. This type of simultaneous interpreting will be the focus of the rest of this article. However, simultaneous interpreting is also occasionally done via a method called whisper interpreting, in which the interpreter sits next to one or more people and quietly interprets the target language without using any special technology. This method is sometimes used during business negotiations or meetings between dignitaries. It’s best suited to situations where only one additional language is needed and only a small segment of an audience requires interpreting.

A Brief History of Simultaneous Interpreting

Simultaneous interpreting was first conceptualized in the 1920s. However, it wasn’t until the Nuremberg Trials in 1945, during which representatives of Nazi Germany were tried for crimes and atrocities committed during World War II, that the method was popularized.

The multilingual nature of the Nuremberg Trials represented a challenge. The judges, defense and prosecution teams, and defendants spoke four different languages – English, French, Russian, and German. In order to ensure a fair trial, it was essential that all participants have a full understanding of what was being said during the proceedings.

Prior to the trials, the standard way to deal with multiple languages during court proceedings was to employ consecutive interpretation. One speaker would deliver remarks in French, for example, while a number of interpreters took notes. When they were finished, one interpreter would interpret into English, followed by another interpretation into German and then into Russian. All questioning, testimony, and sentencing would have to be spoken aloud four times, ultimately meaning that the trial would take four times as long.

At the start of the trials, however, there was a strong sense of historical urgency. World War II had just ended, much of Europe was in shambles, and the public was eager for high-ranking Nazi officials to be held accountable for their crimes. Nobody wanted the multilingual nature of the trials to mean they would have to stretch on for several additional years.

Still, many people at the time were skeptical of simultaneous interpreting, as it was believed nearly impossible to listen in one language while providing an accurate verbal translation into another. In fact, of the 700 professional interpreters sent to Nuremberg to test the new system before the trials began, only five percent were considered viable candidates for simultaneous interpreting.

The system employed by the trials was a modified version of the first simultaneous interpreting system, which was built by Boston businessman Edward Filene in 1925. The basic principles of how it worked were fairly similar to modern simultaneous interpretation technology.

Attendees wore headphones that were affixed either to a table, a seat back, or their own seat. The headsets had dials that allowed them to manually select their preferred language channel. Channel 1 was the source language – the original language being spoken. Channel 2 was English, 3 was Russian, 4 was French, and 5 was German. So if the defendant spoke French, for example, Channel 1 would broadcast in French, and the Channel 4 interpreter would be silent. Meanwhile, the English, Russian, and German simultaneous interpreters would all be speaking into microphones and delivering real-time interpretations of the French.

Ultimately, the trials required the work of 108 interpreters, translators, and stenographers whose work was instrumental in allowing for an efficient trial at such a heightened moment in world history.

Benefits of Simultaneous Interpretation

With the second and third booms in globalization following the Nuremberg Trials, simultaneous interpretation has become more relevant today than ever before. Where it previously was used mostly in international tribunes, diplomatic meetings, and the like, today it’s a method utilized in local courtrooms, business or board meetings, large-scale conferences, lectures, and presentations of all kinds.

In addition to efficiency, because the information is relayed with a delay of only a few seconds, simultaneous interpretation allows listeners to benefit from the original speaker’s gestures, facial expressions, and other nonverbal cues. Having no artificial gaps or pauses in speech can also help listeners take in information in a more fluid manner, allowing for better processing and retention of what is heard.

Additionally, simultaneous interpretation is highly personalized. Even where attendees have a passing knowledge of the speakers’ language, offering interpretation into their preferred languages can help build positive relationships. Research has shown, for example, that seventy percent of customers feel more loyal to companies that offer support in their native language.

Overall, simultaneous interpretation tends to be the best choice at multilingual conferences or presentations during which large amounts of information need to be shared relatively quickly.

Challenges in Simultaneous Interpretation

As previously mentioned, simultaneous interpretation can be incredibly taxing for the interpreter. Most simultaneous interpreters can only render quality interpretations for about twenty to thirty minutes at a time before their focus begins to wane. Therefore, it is common for simultaneous interpreters to work in pairs and trade off every few minutes. As at least two interpreters need to be hired, simultaneous interpretation tends to be more costly than consecutive interpretation.

Simultaneous interpretation also requires technology suited to the type of event, the number of attendees, and the number of target languages. This is another reason it is generally quite a bit more costly than consecutive interpretation.

How does it actually Work?

As mentioned above, in principle, systems for simultaneous interpreting are not too dissimilar to the ones first used nearly a century ago during the Nuremberg Trials. A speaker talks into a microphone, and their speech is broadcast to one or more interpreters listening through headphones from a soundproof booth. The interpreter listens and then speaks into a microphone as well, translating into the target language in real-time. Their message is then wirelessly transmitted to event attendees’ headphones.

Choosing the Right Equipment

Though simple in principle, simultaneous interpreting does require a fair amount of specialized equipment. When planning an event, there are two main simultaneous interpreting systems to choose from: an infrared system and an FM system.

Infrared systems

Infrared systems are best for events where security or confidentiality is of concern or where more than eight languages need to be interpreted. They are line-of-sight, meaning that if receivers (used by attendees) are not within view of the IR Emitter, they won’t be able to receive a signal. Signals can also be interrupted by bright or flashing lights. These systems can be used both indoors and outdoors and tend to be more costly than FM systems.

FM systems

FM systems, which use radio frequencies to transmit a signal, are best for events where security is of low concern and less than eight languages need to be interpreted. They are not sensitive to obstructions, and generally have a range of up to one thousand feet, making them a great option for larger-scale conferences or events. Some FM systems are also portable and can be used for walking tours in museums or outdoors.

Interpreter booths

Perhaps the biggest technical change we see from early simultaneous interpretation systems like those used during the Nuremberg Trials is the incorporation of soundproof booths that allow interpreters to speak at full volume, producing a clear transmission without any concern about interrupting or distracting the presenter.

By eliminating external distractions, interpreter booths also help aid interpreters’ concentration. Additionally, they ensure there is no background noise in the message transmitted to the target audience. A clear line of sight to the speakers, the podium, and the presentation, as well as strong internet access, are essential when positioning an interpreter booth.

Tabletop booths

As the name suggests, tabletop booths sit on top of a table. Their main benefit is that they are easy to transport and set up. However, while they reduce some background noise, they are open in the back, meaning that they are not entirely soundproof. As such, they may be a somewhat less ideal work environment for interpreters than full-size booths.

Full-size booths

Full-size interpreting booths are fully enclosed capsules that look like little houses. They have a floor, ceiling, and walls, as well as their own ventilation systems, and they can accommodate anywhere from one to four interpreters (though two is most typical). Although they are more difficult to transport and set up than tabletop booths, they are fully soundproof and generally provide a more private and comfortable working environment for interpreters.

Innovations: Simultaneous Interpretation Apps

Simultaneous interpretation apps are a new alternative to traditional simultaneous interpreting technologies. They can be used during remote events, such as online conferences or webinars, or at in-person events.

The apps are mobile systems that use local Wi-Fi or listeners’ mobile data to stream audio in real-time. Similar to traditional systems, the speakers’ audio is first transmitted to interpreters who then render the message into the target language and transmit it to the listeners’ phones using either a traditional console or a specialized broadcaster.

One of the main benefits of simultaneous interpretation apps is their versatility. Presenters, listeners, and interpreters can all be in the same location, in different locations, or the event may be hybrid in nature. If the event is held in person, for example, the interpreter can still be off-site, eliminating the need for interpreter booths. Similarly, if some audience members or even presenters are unable to make it to an in-person event, simultaneous interpretation apps can accommodate virtual attendance, as they allow people to listen or stream from anywhere.

What to Look for in an Interpreter

Considering the challenges of simultaneous interpretation, it’s important when hiring an interpreter to ensure they are experienced in this particular mode of interpretation (not only consecutive interpretation). Additionally, if the event will involve the use of industry-specific concepts or terminology, interpreters should have a working knowledge of the industry and be prepared to interpret challenging, jargon-dense content. To ensure everything runs smoothly, it can be useful to provide interpreters with event materials in advance.


From its earliest iteration in the 1920s to its popularization during the Nuremberg Trials to its current global proliferation, simultaneous interpretation has been an innovative method for accommodating the rapid increase in multilingual audiences and events seen as a result of globalization. Though somewhat more costly and involved than consecutive interpretation, simultaneous interpretation offers greater efficiency and fluidity in the presentation of large quantities of information and can help multilingual audiences feel valued.

If you’re planning an event requiring simultaneous interpreting, get in contact with ALTA. We offer all-inclusive simultaneous interpretation services, from matching you with high-quality interpreters who understand your industry to simultaneous interpretation equipment rentals (we’ll help you figure out exactly what you need for the event you’re planning) and even remote simultaneous interpretation options. We’ll also set you up with a project manager to help you plan and execute your event without a hitch.

Get in contact with ALTA to make your next meeting, conference, or lecture accessible to everyone in your audience.

Janet Barrow holds a B.A. in Written Arts from Bard College and a Master of Speech-Language Pathology from the University of Sydney. She works as a pediatric speech pathologist and freelance writer and is currently finishing her first novel.

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