Records a hum against a click and turns it into a song, for mix mx.hum --record.

The click is mx's closed hi-hat, a tick without a pitch, louder on the first beat of each bar: a bar of 4 beats as a count-in, then every beat until wait returns, which is when Enter is pressed. The sound card's input is recorded from the first click, apart from the main output, so the click is not in the recording, and a click the microphone picks up from the speakers has no pitch to be a note. Beat 0 is the first beat after the count-in, and a note hummed during the count-in is left out.

Whatever can be refused is refused before the first click: a recording or song that exists without force:, a folder that cannot be written, and an input that runs at another sample rate than the output.