Initial time gap
The initial time gap ( English initial time delay gap , ITDG ) is the time between the arrival of the direct sound and the arrival of the first strong reflection is. It arises from natural listening in rooms and concert halls, but also from loudspeaker stereophony . Here an additional first reflection is usually generated in the playback room within the recorded ITDG.
In addition to the frequency response and level of the direct sound D and the room sound R, the ITDG determines the perceived distance to the sound source . In large concert halls, the proportions of high frequencies in direct sound and in room sound are influenced by temperature and humidity . The ratio of direct sound to room sound is important for the impression of space, whereby the gap between the beginning and the early reflections plays a major role in natural hearing .
The importance of the initial time gap in natural hearing for the proximity impression of a sound source
The initial time gap associated with distance hearing varies in length, depending on the distance of the respective sound source from the listener and the location in the room and the shape of the room with its reflective surfaces. Sound sources make a clear close impression in the room when the initial time gap is long and the room sound has a low level and make a nebulous and distant impression when the initial time gap is short or nonexistent and the room sound is high in relation to the direct signal.
If the initial time gap is less than 15 ms ( pre-delay ), a small-scale impression is created. If the time gap is greater than 30 ms to approx. 60 ms, the result is a spacious and transparent sound impression. It is advisable to set this pre-delay gap large in reverberation devices and to shorten it only if necessary.
With a reverberation device, the pre-delay does not correspond to the natural conditions in the room because it is only a fixed time setting. In a room, each sound source creates its own differently large initial time gap, depending on its location. Accordingly, it is incorrect to call the initial time gap a space constant, as can be read in textbooks. The initial time gap depends on the location of the sound source and the location of the listener or the measurement location. For the sonic effect of the artificial reverberation, the special importance of its mixing level should be pointed out.