Although there is some overlap in the effects of acoustical treatments and sound masking, the purpose of each is quite different.
Acoustical treatments are used to quiet a noisy space by absorbing and/or diffusing sound waves. Installing these products in a gymnasium or school cafeteria would decrease the overall noise level and make it easier to hear a nearby talker.
Sound masking systems are used to obscure speech by injecting background noise (somewhat similar to the sound of rain) into a space. These types of systems can provide privacy in settings such as hospitals or law firms. In addition, they can help reduce distractions in noisy areas such as call centers.