Echo machine

Propagation delay is in electro-acoustics and sound a name for

With decentralized sound system, so in the transmission of a large circle of listeners in stereophonic and surround sound technology can double hearing or multiple hearing and thereby reduced intelligibility and reduced transparency ( Acoustic ) occur when the propagation time difference between the sound events of distributed speakers and possibly the original sound to the ear of the listener 50 ms, corresponding to a Laufwegunterschied of about 17 m, exceeds or if the sound level differences Δ L are greater than 6 dB; see also echo threshold. Applies to both, it shall be for avoiding the defects to approximate the different sound propagation times. In order to further ensure the localization of the original sound source ( primary sound source), also has yet to be ensured that the original sound ( primary sound ) to several milliseconds earlier in the listener arrives as the delayed speaker sound, and this then even up to 10 dB above the level of the may be original sound without the localization process is impaired; see also the Haas effect.

For the time delay of signals have purely electronic operating delay devices, mainly enforced in digital technology. For example, if an original sound event are emitted by loudspeakers, the different distances from the sound source ( the orchestra ) are arranged so thinks you look concentric circles around the original sound source and delays the sound radiation of all lying on such a circle speakers to the radius corresponding period of the sound. The listeners are then sonicated in phase by all located in the direction of the original sound source in front of them speakers, while the back and side lying speakers are practically not perceived because of their directivity.

For sound recordings with multiple microphones at different distances from the sound source to the microphone signals by propagation delay "in phase" can bring, so that frequency-dependent partial cancellation when mixing or at the listening position be avoided. This is the sometimes applied in the recording technology of the delayed spot microphones.

With propagation delays can be the impression of additional space depth produce. Furthermore, propagation delays are used for artificial reproduction of early sound reflections, or to reverberation and also contribute to the impression of space in.