Do sound waves travel faster in air or through a radio signal. Why?

Sound waves cannot travel through a radio signal. It is the vibration of mater and radio waves don't carry sound. You can transmit a representation of sound through a radio wave but it is not really sound and needs to be translated back into sound at the receiver. Radio travels at the speed of light and is much faster than sound.

The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In air at sea level, the speed of sound is approximately 343 m/s, in water 1482 m/s (both at 20 °C, or 68 °F), and in steel about 5960 m/s.[1] The speed of sound is also slightly sensitive (a second-order effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).

You can read more if you want to in this website