When specifying an instrument number without a note, ProTracker 1/2 instantly applies the new instrument settings, but does not use the new sample until the end of the (loop of the) current sample is reached. In this example, sample 2 should be played at maximum volume as soon as instrument number 1 is encountered in the pattern, then sample 1 should be triggered somewhere around row 10 and then stop playing at around row 18.