The wavelength is determined by the amount of time between peaks or valleys in the pressure, not the amplitude of them. Said differently, the speed of sound is nearly independent of the pressure, so if the time is known, then the distance can be solved for, as simply wavelength (meters) = speed of sound (meters / second) divided by frequency (Hz or cycles / second). In other words, the wavelength depends only on the speed of sound and the frequency, but not the amplitude.