vuvuzelas. There have been varying approaches to the practice, including whether the sounds are played over a venue's audio systems or only for television viewers, and whether the audio is synchronized in real-time to correspond with in-game events. It is usually mixed by an audio engineer on-site, but some events have also employed mobile apps that allow viewers to influence the sounds by voting on reactions. The Philadelphia Union employed a member of their supporters' group to provide input to the sound engineers. For the 2020 US Open, IBM trained its Watson artificial intelligence system to cue crowd noise automatically, using footage from past editions of the tournament to determine appropriate reactions to in-game events. In some cases, artificial crowd noise has been paired with the use of augmented reality to fill in empty stands with CGI "spectators" (as used during La Liga and trialled by U.S. broadcaster Fox Sports), or the use of virtual audiences that are displayed on video boards within the venue. The practice has been met with mixed reception from viewers and sportswriters, usually dependent on the quality of the execution. One football writer argued that artificial crowds were "disingenuous" and created a disconnect with accounts of games noting the lack of spectators, and felt that viewers were missing out on the ability to hear on-field communications between players, arguing that "if a game that generally produces one of the most fierce atmospheres in the world is being played in front of a silent backdrop, that's as much a part of the story as the result." See also Laugh track References Sports terminology Sound recording Television terminology Impact of the COVID-19 pandemic on sports