TIMING
To understand what a reverberant sound actually is and what information our hearing system is able to extract from it, you need to think about how sound waves travel and what happens when they encounter various surfaces.
去了解一下混响声音实际上是任何形成的,以及我们的听觉系统能从中获得什么其他信息,有必须去思考声音是如何传播的,以及他们遇见不同材料的平面后,会发生什么问题。
The first thing to consider is how fast sound travels in air. My old school physics books said 760mph and the new ones probably say 340 metres per second, but I find it hard to relate these numbers to anything meaningful (other than the average speed of traffic around the Evesham bypass in the morning....).
首先要做的时候去了解声音在空气中的传播速度。我以前学校的物理课本说是760MPH,而新书就说一般情况下340m/S,但是这不能用于所有的情况(这是平均速度)。
A much more useful figure to tuck away in the dark and dusty recesses of your mind is that sound travels roughly a foot each millisecond. Assuming that you're not too young to relate to feet as a valid dimensional measurement, this rule of thumb will allow you to calculate and set one of the most critical parameters of any reverb processor. One quick side note: the speed of sound varies with the condition of the air. Temperature, humidity and pressure (ie. altitude) all have significant effects on the speed of sound, and in certain applications the 1ft/ms guide is not sufficiently accurate. However, as far as dialling up room sounds on a reverb unit is concerned, it's close enough. Imagine that you're standing in the middle of a very large, brick-walled barn with a deep covering of straw on the ground. You have a spontaneous urge to clap your hands: what happens? Well, the very first thing you'll hear is the direct sound of your hand clap, and it's this direct sound that the brain uses to pinpoint the direction of the sound source.
一个更加常用的描述是在你认为黑暗而且干燥幽静的地方畅饮,那么声音传播的速度就是1步长=1MS。这个单凭经验的办法能让你去计算以及设置所有REVERB的参数。从侧面可以知道:声音的速度受空气条件的影响而出现变化。温度、湿度和气压(例如海拔高度)都对声音的速度有重要的影响,而运用1FT/MS作为标准依据也不是非常准确的。但不管怎样,在REVERB效果器上改变声音的远近,和上面的说法都有非常密切的关系。假设你站在一个用砖瓦搭建的空空荡荡的房间中间,以及铺上一层比较厚的稻草。你随意的鼓掌几下:会发生什么事情呢?首先你会听到你鼓掌的时候,发出的直达声,脑袋就考这个直达声来确定声音的方向来源。
Assuming that the hand-clap radiates sound waves in all directions simultaneously, the next thing you'll hear will be reflected sound from the various room boundaries or nearby objects. As the floor of this imaginary barn is covered with a deep layer of straw, there will be no significant reflection from the ground (although in practice this is often a dominant source), so the first 'room sounds' will be reflections from the side walls and ceiling. If the barn measures 40ft by 60ft and is 20ft high, and assuming we're standing in the middle of it, the very first reflection will come from the roof, after about 30 milliseconds.
同时,鼓掌声同时向所有方向辐射出去,然后你就能听到来自房间所有角落或者其他物体反射回来的声音。而这个房子地面铺上一层稻草,这样使得地面不会有太大的反射声音产生(实际上地面的反射回来的声音经常是反射声的主要来源),所以最早听到的反射声是来自周围的墙壁和天花板。如果这个房子的规格是40ft(步长)*60ft(步长)*20ft(步长),以及我们站在房子的中间,那么最初的反射生来自房顶(距离最短嘛),大概用了30MS。
This time delay can be estimated by working out the distance the sound wave has to travel -- if you're a man standing up in the barn, your hands and ears are likely to be about four and six feet respectively above the floor, so (20-4) + (20-6) = 30. Sound travels roughly 1 foot a millisecond, so it will take 30ms for the sound of the clap to reach the ceiling and return to your ears. Similar calculations reveal that the side-wall reflections occur 40 and 60ms after the initial direct sound.
这个时间上的延迟能在声音传播的距离上作出估计——如果你站立在这个房子里面,你的手和你的耳朵分别高于地面大概4到6步长,所以(20-4)+(20-6)=30(这里20-4是手到屋顶的距离,20-6是屋顶的声音反射回你耳朵的距离,声音传播是1步长/MS,声音的传播方向是手掌->屋顶->你的耳朵)。利用同样的就算方法,四周的墙壁反射声音大概会在直达声音之后40ms和60ms左右出现。
"...artificial reverberation is not only more affordable than ever before, but can also be stunningly realistic and very controllable."
The time taken for these first reflections to be heard goes a long way towards defining the perceived acoustic size of the room. Short delays imply small rooms, and long delays large rooms. To mimic this natural characteristic, artificial reverberation units normally allow the user to set the time delay between the direct sound and the very first reflection with a parameter called Pre-Delay. This is generally adjustable in millisecond increments (or finer) over an astonishingly wide range.
初次反射声音在传播一段距离之后被你所听到,这段距离所消耗的时间被认为是有利于定义这个房间的声学感觉的大小,从而判断这个房间的大小。短延迟代表这个是小房间,而长延迟代表这个是大房间。在模拟这个自然特征上,混响效果起一般都允许用户去设定直达声和初次反射声(这里用VERY是特制最最最早的那些,但是在小房间里面比较难区分,大空间就比较好区分了)之间的一个时间延迟,这个参数控制我们称为PRE-DELAY(预延迟)。混想器一般情况下,通过调节MS来增加(或者变得更好)声音的宽度。
So the first reflection comes from the closest surface, and is followed by others from the adjacent room boundaries, the whole ensemble being known as Early Reflections. The timing, relative amplitudes and timbre of these individual reflections are determined by three things: the placing, angles and nature of reflective surfaces; the location of the sound source; and the position of the listener. Moving any of these will change the relative timing of the early reflections quite significantly, but our hearing system is remarkably good at extracting even the most subtle information. Consequently, these initial reflections and their relative timing are very important in defining an imaginary acoustic space.
所以初次反射声是来自最接近的反射面,然后是紧接着来自其他临近墙壁的反射声,而所有这些声音就被称为EARLY REFLECTIONS(早反射,非硬件/效果卡支持的PLUGINS好像就只有WAVES有这个设置,而WIZOO是采样REVERB,是采样决定这个ER,所以没有很明确的关于这个参数的设置)。时间上的选择、相对幅度以及这些独立反射声的音调都是由三样事物所决定:第一是现场、房间里面的角落和自然反射面;第二是声源的位置;第三是观众的位置。改变这些东西中的任何一样东西,都会对早反射的相对时间有十分重要的改变,但我们的听觉系统非常善于发现这些微小的变化。因此,这些初次反射声和他们的相对时间对于定义假设声学空间是非常重要的(REVERB PLUGIN就是在做一个假设的声学空间)。
The better reverb units allow the user to alter not only the value of the pre-delay, but also the number, grouping, timing, amplitudes and tonal qualities of the first reflections. In some cases, these parameters are preset by the manufacturer and are simply selected from a list of programmed options, such as Hall, Chamber, or Plate, although occasionally they are derived from measurements taken in genuine acoustic environments. The most sophisticated machines allow the user to specify the cubic volume of the imaginary room, or even its precise dimensions, together with the source and the listening positions!
一个优良的混响效果器都允许用户改变预延迟参数重不只是PRE-DELAY,还有数量(ER的数量,参考WAVES IR1),种类(不同的类型选择,例如HALL / PLATE等等)、时间设置、振幅和音调的选择(这里在非硬件支持重比较少有)。所以大家可以在REVERB效果起重设置不同的房间参数,来改变房间的特性,变成HALL/CHAMBER/PLATE等等,甚至有些REVERB效果器还能选择声源位置和听者的位置。
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本帖最后由 Ying 于 2006-7-31 21:17 编辑 ]
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