Research experiment or classical music concert? The Golden Ear Challenge is both. It brings the University of Oldenburg's hearing research to the concert hall and at the same time generates exciting data for scientists.

The four musicians of the string quartet on the stage at the Exerzierhalle look each other in the eye for a moment, then take up their bows and begin to play. The first strains of Beethoven's String Quartet No. 3 float towards the audience – and then stop after a few seconds as suddenly as they began. A murmur ripples through the audience, almost 100 smartphone displays light up simultaneously, and as a clock counts down on a large screen behind the quartet, the members of the audience all ask themselves the same question: which of the four instruments played a wrong note? Then they enter their answer into the online survey tool that they logged into before the start of the event. Today, they are not just guests at a concert but also part of an experiment.

The experiment is led by Kai Siedenburg, who recently took up a post as a professor at the Graz University of Technology but still heads the Music Perception and Processing research group at the University of Oldenburg. "We normally do our experiments in the lab and put our test subjects in an isolated sound booth for one to two hours," Siedenburg explains to the participants in the concert experiment. "But we wanted to see whether we could also do this live and with a real concert audience."

To perform the live experiment, which is sponsored by the Volkswagen Foundation, the researchers are on a "research tour" with the Orchester im Treppenhaus string quartet from Hanover. After concerts in Bremen and Hanover, the Oldenburg event at the end of November was the penultimate stop for the Golden Ear Challenge and the quest to determine which participant had the best hearing of the evening. For anyone interested, the concert on 7 March at the Elbphilharmonie in Hamburg is the last chance to take part in the challenge.

Hearing impairment is an important issue for musicians

Playing at a series of events where they have been asked to deliberately make mistakes doesn't go against the work ethic of these professional musicians. On the contrary: "The goal of providing people who suffer from hearing loss with hearing aids that can also make listening to music more enjoyable is very important," says violinist Johanna Ruppert. Moreover, musicians in particular tend to suffer from hearing loss in old age as a result of constant acoustic stress. "So it's also in our own interest that the focus is on hearing health here," she adds.

The mistakes that the quartet have incorporated into the short audio samples in consultation with the researchers pose a challenge for the audience, and not just in Oldenburg. "Was there a mistake at all?" one member of the audience calls out after one of the sequences, and others in the audience laugh in agreement.

On this particular evening no one is able to tell in all six Beethoven excerpts of the first round whether it was violinist Moritz Ter-Nedden, violinist Johanna Ruppert, violist Erin Kirby or cellist Michael Schmitz who made an error. The sounds of the string instruments merge too seamlessly into a single product. This is precisely the goal of Siedenburg and his team's experiment: based on the responses of the members of the audience they aim to determine which factors influence how people differentiate between individual sounds when listening to a combination of sounds. "How we hear depends on neurobiological and other factors, but the anatomy of the ear also influences how sound is processed," explains musicologist Dr Iris Mencke. "The culture and music we grew up with play a role too, just as our hearing health does."

Previous practical experience such as having regularly played an instrument can also help determine how well someone can distinguish subtle nuances in music. This is why all participants are asked to provide information about their previous musical practice and some key statistical data in the online survey.

Skilful playing disguises errors

The Beethoven round is followed by a second round featuring errors in Maurice Ravel's String Quartet in F major and a third round with errors in Robert Schumann's String Quartet No. 3. As soon as the deadline for entering their answers after listening to the audio samples has expired, the screen behind the stage displays a tally of the audience's responses – together with the correct answer. The musicians seem to take particular pleasure in elegantly disguising their mistakes to avoid being exposed. First violinist Ter-Nedden is particularly adept at ensuring that his mistakes go undetected. "He just plays the mistakes particularly beautifully," presenter Anna Kussmaul comments dryly. In between the test sequences, however, the quartet plays longer excerpts without any mistakes during which the audience can sit back and simply enjoy the music.

The two participants who have detected the most mistakes within the shortest time by the end of each of the three rounds go through to the final, in which a special task awaits them: a dummy head set up in front of the stage plays a key role here. It captures the sounds of the orchestra with its artificial ears and plays them back to the six finalists through a filter that makes them sound like they would to a person with impaired hearing. In this round, the finalists wear headphones and have to listen very carefully. This isn't an easy task for anyone. In an excerpt from Grażyna Bacewicz's String Quartet No. 4, violist Erin Kirby manages to fool all of them. No one notices that it was her who played a false note.

Then the excitement mounts as the winner of the Golden Ear is announced. Dr Daniel Berg takes home the award for the finest hearing that evening. His work at the Hearing4all Cluster of Excellence, where he is responsible for research data management, could only have played an indirect role, if any. "But I do have a slight advantage," he explains. "I sing in an a cappella quintet ¬ and the voices meld just as harmoniously there as the strings do here. But I have to admit: I didn't stand a chance with Beethoven."