RHY.6:5.1 - Positions survive while sound classes disappear

This constructed percussion exercise has two attacks in one beat. Let D and T denote two distinct sound classes under a supplied local convention. They are not a claim about a particular named iqa‘.

The target preserves the two attack positions but cannot distinguish A from B. It is sufficient for asking where the attacks fall. To reproduce the sound-class order, retain (D, T) or (T, D) associated with those occurrences.

Now shift A’s two attacks forward by one quarter of the beat, without changing their sound classes. Their new positions are 1/4 and 3/4, yielding the position reading ka–mi under the four-part convention. D remains with the first shifted event and T with the second. Repeating ta–di after the shift would preserve the old positions, not the requested edit.

The edit can also originate in the target. Suppose the user changes ta–di to ka–mi while keeping the two occurrences and their associated D/T order. Under the selected four-part convention, reconstruct D at 1/4 and T at 3/4. Translating that revised source yields ka–mi; leaving ta–di unchanged leaves D at 0 and T at 1/2 unchanged.

If the user instead inserts a third attack, the two-label companion supplies no sound class for it. Return that missing assignment when the receiving task needs the sound-class phrase; the three positions alone can still serve a positional question. If a companion also demands that the old positions remain fixed, it conflicts with the requested ka–mi edit: resolve which positional requirement changes instead of silently retaining incompatible instructions.

This is a bounded construction of positions and labels. Whether a changed phrase still belongs to a particular musical prototype needs that practice’s identity conditions.