If a wind is blowing, will this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity changed?

When a sound source is moving toward an observer, the pitch that the observer hears is higher than when the source is at rest. And when the source is traveling away from the observer, the pitch is lower. This phenomenon is known as the Doppler Effect, and it occurs for all types of waves.

We analyze the case of the wind blowing from the source toward the listener. The moving air (wind) has the same effect as if the speed of sound had been increased by an amount equal to the wind speed. The wavelength of the sound waves (the distance that a wave travels during one period) will be increased by the same percentage that the wind speed is relative to the still-air speed of sound.

Since the frequency is the speed divided by the wavelength, the frequency does not change, so there is no Doppler effect to hear.

Alternatively, the wind has the same effect as if the air were not moving, but the source and listener were moving at the same speed in the same direction. Finally, since there is no relative motion between the source and the listener, there is no Doppler shift.

Hence, the wavelength of the sound waves will be increased by the same percentage that the wind speed is relative to the still-air speed of sound.