# Runtime difference

The word transit time difference or transit time difference is used:

The transit time difference is usually specified in milliseconds (ms).

## The interaural time difference (ITD)

The interaural transit time difference (or ITD ) affecting humans and animals is the difference or the difference in the transit time of the sound between the two ears . It is of great importance for the directional localization of the sound source , as it provides a feature for recognizing the direction or the angle of the sound source, seen from the head. If a signal is generated in the horizontal plane, the angle is in relation to the 0 ° front direction (i.e. directly in front of the listener) clockwise from 90 ° then exactly to the right and at 180 ° the direction is back. For example, if a signal comes in from 90 ° from the right, then the signal has to travel an additional distance to reach the left ear. For the sound, this results in a time difference between the two ears. This interaural transit time difference is determined by the ear-brain system and supports the recognition process of the sound source.

The azimuth of a sound source can u. a. can be determined by the time difference with which the sound event reaches both ears. This means that the sound reaches one ear earlier than the other. If a sound comes from the left side, it reaches the left ear first. The right ear is reached later because it is further away from the sound source on the far side of the head. The difference in transit time is therefore dependent on the path that the sound travels. If the sound source is in front of or behind the hearing person (middle of the head), there are no transit time differences. In this case the sound paths are the same length. The maximum transit time difference is 0.63 ms, namely when the sound source is exactly to the side (90 °) of the head. The hearing can recognize transit time differences from 10 µs, so that even small deviations of a sound source from the center of the head can be recognized. In the case of small changes in sound (e.g. clicks ), transit time differences can be distinguished that arise when the sound source deviates at an angle of around 1.5 ° from the center of the head.

The duplex theory contributes significantly to the understanding of the natural hearing process.

## The interchannel transit time difference Δt

The direction of the auditory event of the phantom sound sources on the stereo loudspeaker base can be changed with the generated interchannel transit time differences of the microphone systems on the loudspeaker base. A maximum transit time difference of Δ t max = 1.5 ms (1 to 2 ms) causes the full sideways deflection from the loudspeaker direction, depending on the signal (depending on the pulse shape). These differences in the loudspeaker signals, which vary depending on the angle of sound incidence, are generated by the respective stereo microphone arrangements, which thus also provide the important recording area of the microphone system. The empirically found values ​​of the required transit time difference Δ t for localization on the loudspeaker base (loudspeaker signals) have nothing to do with the measured values ​​of the interaural transit time difference (ITD) on our ears (ear signals).