If not, use a recording or simply sing a cappella.
Christianity Today
Let's hear him sing a cappella and see how many phone votes he gets.
The Sun
Crucially, though, the groups have to sing a cappella.
Times, Sunday Times
Contestants were required to sing a cappella with poor singers often facing intense and humbling criticism from the judges.
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For a few weeks, the congregation sang a cappella, but people began complaining.
Christianity Today