The humdiff filter can be used automatically mark differences between two or more scores of the same length.

Here are two example scores:

And another score with some differences:

The humdiff filter can be given these two scores, and it will highlight the notes in the first score that are different in the second score. Here is an example of using the first score as a reference and highlighting notes that are different in the second score:

By reversing the order of the scores, the second score example can be displayed with notes different from the first score example highlighted in red:

Notice that the humdiff filter is preceded by four !!!! marks rather than the typical three !!! for filters. This is because the filter operates on more than one data segment.

Switching the order of inputs

The chooser filter can be used to re-order Humdrum data segments before processing with the humdiff filter. Here is an example of switching the first and second segments before analyzing with humdiff: