Singing in a chorus usually means a large group of people, belting out songs and nailing those harmonies together -- all in the same place.
A virtual choir, on the other hand, allows the participants to sing from the comfort of their own home -- ideal amid the pandemic when some singers have faced accusations of being superspreaders.
In one instance, dozens of singers in Washington state were infected after a choir practice.
In this latest virtual choir, which debuted on YouTube on Sunday, all the singers learned "Sing Gently," a song Whitacre composed during the pandemic.
"Sing Gently" encourages people to "live with compassion and empathy, and do this together," Whitacre said.
Whitacre started organising Virtual Choirs in 2009, much before the Covid-19 pandemic hit the world.
It started after a fan uploaded a video of herself singing one of his choral compositions.
He saw the video, then asked others to record themselves singing the other parts of the same composition to form a "choir."
That first group featured 185 singers, and each one since has grown larger and larger, to more than 8,000 voices for the fifth performance in 2018.
This year, signups for Virtual Choir have skyrocketed.
More than 17,000 singers from around the world found a way to participate in the sixth recording from the isolation of their own homes.
The Virtual Choir team uses every video submitted, unless there's a technical problem with the recording, Megan Friedman, Features Editor of The Keyword at Google, wrote in a blog post on Tuesday.
That means there are thousands of videos to sync together, and thousands of sound recordings to edit so the result sounds seamless.
This time around, the team featured three sound editors, six people reviewing each submission and two executive producers.
The team was scattered through the US, the UK and South Africa.
Across three different continents, they used Google Docs and Google Sheets to keep track of their progress, Google's webmaster tools to manage thousands of email addresses and Google Translate to keep in touch with singers around the world.
Singers checked the choir's YouTube channels for rehearsal videos, footage of Whitacre conducting the song and Q&As with other singers and composers, Friedman said.
Whitacre said he was struck by the number of participants who told him it felt good to sing with others again -- even though they were not actually performing in the same room.