再贴上一段维基百科的,是英文的.
Haas effect
From Wikipedia, the free encyclopedia
The Haas effect is a psychoacoustic effect related to a group of auditory phenomena known as
the Precedence Effect or law of the first wave front. These effects, in conjunction with
sensory reaction(s) to other physical differences (such as phase differences) between
perceived sounds, are responsible for the ability of listeners with two ears to accurately
localize sounds coming from around them.
When two identical sounds (i.e. identical sound waves of the same perceived intensity)
originate from two sources at different distances from the listener, the sound created at
the closest location is heard (arrives) first. To the listener, this creates the impression
that the sound comes from that location alone due to a phenomenon that might be described as
"involuntary sensory inhibition" in that one's perception of later arrivals is suppressed.
The Haas effect occurs when arrival times of the sounds differ by up to 30 - 40
milliseconds. As the arrival time (in respect to the listener) of the two audio sources
increasingly differ beyond 40ms, the sounds will begin to be heard as distinct; in audio-
engineering terms the increasing time difference is described as a delay (audio effect) , or
in common terms as an echo (phenomenon)
The Haas effect is often used in Public Address systems to ensure that the perceived
location and/or direction of the original signal (localization) remains unchanged. In some
instances, usually when serving large areas and/or large numbers of listeners, loudspeakers
must be placed at some distance from a stage or other area of sound origination. The signal
to these loudspeakers may be electronically or otherwise delayed for a time equal to or
slightly greater than the time taken for the original sound to travel to the remote
location. This serves to ensure that the sound is perceived as coming from the point of
origin rather than from a loudspeaker that may be physically nearer the listener. The level
of the delayed signal may be up to 10 dB louder than the original signal at the ears of the
listener without disturbing the localization.
The Haas effect is also responsible in large part for the perception that a complete complex
audio field is reproduced by only two sound sources in stereophonic and other binaural audio
systems and it is also utilized in the generation of more sophisticated audio effects by
devices such as matrix decoders in surround sound technologies, such as Dolby Pro Logic.
For a time in the 1970's, Audio Engineers used the Haas effect to simulate that a sound was
coming from a single speaker in a stereo sound system, when it was actually coming from
both. This was to compensate for the fact that a sound coming from a single speaker would be
3db lower in volume than a sound coming from both. This technique has problems if the stereo
sound is mixed to mono, as a Comb filter effect would occur. Also, the Aesthetics of sound
mixing changed to exclude the use of solo instruments emanating from a single corner of the
sound field in most popular recordings.
Named after Helmut Haas who described the effect in his doctoral dissertation "Über den
Einfluss eines Einfachechos auf die Hörsamkeit von Sprache" to the University of Göttingen,
Germany. An English translation was published in December,1949. [1]
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