Techniques for varying duobinary and modified duobinary, which are two of the most important partial-response codes, to limit their run lengths without destroying their minimum bandwidth property, are introduced. One of the example codes is the first run-length-limited variant of duobinary ever known, and the other two are already publicized variants of modified duobinary, but are described either in more detail or from a different point of view. Performance figures of the three codes such as power spectrum, eye width, and error probability are experimentally confirmed to be acceptable for all engineering purposes.