A white noise maker is a device typically used for sound masking, either for the purpose of aiding sleep or to enable privacy in environments where sensitive conversations would otherwise be overheard such as doctors offices or meeting rooms. In addition to their use in sound masking there are white noise machines available that are specifically tailored for use in “noise therapy” whereby the white noise is employed in the treatment of tinnitus.
The white noise makers that are marketed as sleep sound machines can be one of two types of devices. The first type is a mechanical white noise maker, which will typically use a fan to generate the required white noise, while the second category are digital machines that actually play recorded loops of pseudo-random white noise. Although these are not true white noise makers (see below) this second type of machine is usually far cheaper to purchase and operate, and can be equally effective, with the added benefit that they often include other sounds that are not necessarily white-noise, but provide an alternative if you find the white noise function ineffective for whatever reason. However, it is the mechanical fan-based machines that are usually employed for conversation masking.
Note: In reality most digital white noise devices actually generate pink noise, which isn’t as harsh or “ragged” as true white noise. Even mechanical white noise machines that use fans to create the required effect generally produce pink noise, as you’ll notice if you compare the sounds generated to true white noise like the static generated by an untuned FM radio.