ignored (new PBD::IgnorableControllable()),
/* max 1 second, step by frames, page by msecs */
adjustment (initial_value, 0.0, sample_rate, 1.0, sample_rate / 1000.0f),
ignored (new PBD::IgnorableControllable()),
/* max 1 second, step by frames, page by msecs */
adjustment (initial_value, 0.0, sample_rate, 1.0, sample_rate / 1000.0f),