Click here to purchase the entire book in PDF format. Interaural Cross-correlation As we saw in the previous section, a cross-correlation measurement tells us, frequency band by frequency band, how similar two signals are. If we put a dummy head (a simulated human head with microphones in its ears) in a space and connect the outputs of the microphones in its ears to a machine that measures cross-correlation, then we are making an interaural cross-correlation (or IACC) measurement. We'll talk more about the cross-correlation of the outputs of two microphones later, but let's think a little bit about this now... Put two microphones in a room at about 17 cm apart (the width of your head) and think about how similar their outputs will be. At very low frequencies, the wavelength of the sound in air is much much bigger than the distance between the microphones, therefore the pressure at the two microphones will be almost identical. The lower the frequency, the more similar the two signals and the higher the correlation. In theory, if the sound source is directly in front of the dummy head, the room is exactly symmetrical, and the head is on the line of symmetry, then the sound at the two ears will be identical. Therefore, the IACC will have a high value at all frequencies. In reality, the signals will never be identical, therefore you will have a varying correlation value at different frequencies. DOUBLE CHECK ALL THIS TO MAKE SURE I'M ON THE RIGHT TRACK, AND FINISH IT OFF.