Modulation depth m ranges from unmodulated to fully modulated sounds

Evidence

The amount of modulation is controlled by the parameter, m, which ranges between 0 (an unmodulated sound) and 1 (a fully modulated sound). … Note that even the unmodulated sound has an envelope, but it is flat over time, reflecting the steady nature of this sound. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1001

Categorization

• DEFINE: Defines the modulation depth parameter m and clarifies that even steady tones carry an envelope.