现场音频混音的最佳实践

In 2014, I made a presentation at 流媒体 West covering all the various ways an “音频混合忍者得到最好的音频. 当涉及到流媒体的实时音频(下面的图1), there are a few additional wrinkles to consider that don’t come into play with audio recording when you aren’t streaming live.

图1. It takes a team to live stream, from producers, video, audio, lighting.

衰落、限制和压缩

假设我的音频非常出色. 没有嘶嘶声. 好听、有力、干净的声音. That means I’ve mastered the input trim on the microphone I’m using—especially those on wireless transmitters—and set it so it’s not so loud that the audio clips, 也不要太安静，这样会迫使我增加收益, 产生额外的嘶嘶.

音频混音器也是如此(下面的图2). With upward of four places I can adjust a single microphone’s audio, it's easy to get lost. 如果我的混音器有能力独唱一个频道, I’ll use that and have my subjects speak at “program level” while I adjust the input trim. 这是关键. They need to act like it's the actual event and speak, sing, play, shout, at that same level.

图2. 四种主要的方法来调整混音器上的音频水平

如果我在做运动, 让工程师一边说一边设定水平, “你好, 你好, 1, 2, 3, 4” at a conversational tone is nothing like the level at which the announcer will be shouting during a fantastic play. I need to be aware that live events will have much more dramatic audio than, 说, 一个低调的公司网络直播, 并相应地调整我的水平.

Then I have the channel fader to bring up quieter parts of the discussion and bring down the loud parts. 也许还有子混音组(所有的舞台麦克风), 与所有的地板麦克风相比), 然后是主渐变器. But what helps even out all these levels after the mixer are the limiters and compressors.

While the two terms are often used interchangeably, the two are not the same thing. 限制，就像一个限制，意思是“不能超过这个。.” It works to stop the audio from getting any louder than a given threshold. Usually, I can set where that threshold is, and that’s pretty much it. While this achieves the purpose of not allowing the analog audio to clip before being digitized, it can sound strange when audio has normal dynamics one moment and suddenly doesn’t the next.

A compressor, however, can vary its limiting effects on a curve depending on how loud something is (下面的图3). 例如，更安静的东西会有更少的压力. 和, 随着声音越来越大, 压缩级别可以设置为递增, 直到它在最响的地方有最大的压缩. 甚至还有组合限制器/压缩机.

图3. 限制器/压缩机的一些设置方法

What these limiters and compressors do is keep the loudest part of our audio from hitting the digital zero—where it clips and creates a “square wave,而不是平滑的正弦波. 在大多数情况下，这种数字剪辑对我们的使用来说听起来很糟糕. Although musicians can use clipping differently to create specific audio effects for instruments or voices, 那不是我们要找的.

要尽可能避免裁剪. 然而, I’ve heard clipping audio even when the faders on the mixer were not up that high and the output of the mixer was going into a compressor. The operator was confused because the output level was being properly handled—it was low, 虽然没有赤字，但听起来还是很糟糕.

But the operator forgot that audio clipping can happen at the input of the mixer (input trim) or even at the input of the wireless transmitter, 如果有的话. 不管我后来怎么调整, 如果它在音频链的较早阶段剪辑, no amount of lowering the audio level at later stages will fix the clipped audio; it just makes it quieter.

如果我看着搅拌机, 或者压缩机, 没有任何东西在剪切, the audio can still be distorted if the person speaking is shouting to an audience, 为进球欢呼, or simply beyond the audio input levels at any stage of the process.