Doppler Effect

So, while this isn't the best physics journal photo i've ever taken I think it clearly shows the true spark of realization of physics concepts in the real world (especially the bluriness and off-center-ness). So when walking around this weekend I experienced the Doppler Effect via this fire engine's movement and siren/horn. The Doppler Effect is the percieved change in frequency of a sound wave due to movement of the source of the sound or the one listening to it in relation to the source. As the fire engine sped toward me there was a build up of sound waves as it continued to get closer, resulting in a percieved higher pitch, yet the siren and horn are only single pitchs. Once the fire engine passed me and proceeded away from me, the listener, the sound waves reached me in longer intervals, which made me percieve a lower frequency, and thus lower pitch. If my iPhone somehow could have recorded the speed of the fire engine and the frequency of its siren while I took the picture and I could assume my speed, it would be possible to determine the frequency I percieved through the equation: fn=f((v+/-vL)/(v-/+vS)), where v is the speed of sound. This equation states that while the listener moves closer to the source or the source moves toward the listener the percieved frequency is higher, whereas when the listener is moving away from the source and vice versa the percieved frequency is lower.