  Wave is crucial to acquiring information from the world and its interaction
with matter is determined by the wavelength, or frequency. Search for the
ability to shift frequency often points to material nonlinearity, which is
significant only when the excitation level is very high. Temporal modulated
material is expected to shift sound frequency in a linear manner, but is so far
not effectively realized due to inadequate modulation ratio. This study
introduces a new class of temporal modulation material with a giant modulation
ratio. When the modulation is given in a random time sequence, a monochromatic
sound wave is converted to a white noise of a continuous frequency band. The
demonstrated device is called a randomized acoustic meta-layer, consisting of a
suspended diaphragm shunted by an analog circuit. The circuit alters the
acoustic impedance of the layer which operates in two quantized states when the
shunt is connected and disconnected by a MOSFET with a pseudo-random time
sequence. The device has unprecedented potential applications such as
converting annoying tones to white-noise-like hum to improve psychoacoustic
quality, allowing encrypted underwater communication, and super-resolution
imaging.
