如何掌握现场制作和流媒体的音频混音

现场音频具有挑战性. 不像在视频方面出现的许多问题, 没有任何影响音频质量的问题——射频干扰, 反馈, 地环路嗡嗡声, 嘶嘶声, 可以看到过度调制. All of these challenges take a knowledge and understanding of the problem to assess and fix them properly. 关于现场演出, 通常, 修复音频问题的时间是在你听到它们开始发生的时候.

你可能会发现自己在混频器的输入上处理过调制, 或者你的混音器均衡性不好. 您的电位器或退频器可能过高或过低, 之后你会发现自己在混音时试图弥补它. Or your master audio may be distorting, which means you need to try to tamp it down.

最后是可怕的反馈. Most of these are problems you can learn to address by mastering the controls and features of a good audio mixer (图1, 右页), 或者——更好的是——有指导意义的演讲者, 人才, and other members of your crew on how to make proper use of the technology in their hands so that they send you a clean and usable signal.

图1. Behringer Eurorack UB1222FX-PRO专业音频混频器.

麦克风位置

One of the most important things you can do to ensure good audio is proper microphone placement. 例如, 你可以在扬声器的机身上使用一个好的lavaliere麦克风, 而不是讲台上的麦克风，他或她可以走开, 或者一个手持麦克风，他或她可以在空中挥舞. 如果场地特别嘈杂，你甚至可以尝试使用耳机麦克风. These have become much more discreet and more socially accepted when the situation warrants it.

同时，确保你的源音频不会淹没你的麦克风. 通常, 音乐就是这样, 例如, when your performer is using a vocal microphone for drums or a harmonica and the audio distorts at the microphone. 但如果你为轻声说话的人设置了麦克风，也会发生这种情况, 然后把它交给一个足球教练，他会在房间后面大声喊出一切. You can adjust the input level of your wireless microphone so that it picks up a good signal, 但不会过度调制.

对于手持麦克风，“尽可能靠近嘴巴”的规则适用. 如果你曾经主持过婚礼或其他活动，注意看DJ. dj知道如何使用麦克风. A DJ might stand in front of the speaker—which will often cause 反馈—but hold the mic extremely close to his or her mouth to avoid talking very loudly. 系统也会被设置成，除非麦克风进入扬声器, 它不会产生反馈.

When it comes to an instrument mic, naturally, the best approach is to put the mic on the instrument. 在一些作品中你可能会遇到, 说, 一个原声吉他手想要在一个支架上对着麦克风演奏. 这比乐器上的吉他麦克风离乐器远得多, 哪一个会接收琴弦和腔室的共振, and give you much better leeway in the rest of the chain to avoid 反馈 and other issues.

These are all areas in which effective mic placement—and aggressive mic guidance from you—can make a big difference in the quality of the audio you capture and deliver.

压倒性的源音频

In situations where audio recording issues arise from source audio overwhelming the microphone in use, the first thing you want to check is the sound pressure level (SPL) of your microphone. 麦克风有声压级评级, 这取决于麦克风的类型, 麦克风的制造商, 还有麦克风的大小.

很多人用的一个麦克风是美国舒尔 SM-58. It’s a classic vocal mic that’s great for certain tasks and not so great for others. 例如，SM-58的声压级为94dB. 从这个角度来看, some common approximate sound pressure levels include 110dB for an airplane taking off, 或100分贝的摇滚音乐会. If you’re working with the SM-58 on a live event and recording a loud instrument such as a kick drum or trumpet blaring right into it, 这种声音很容易淹没麦克风，扭曲音频.

使用无线麦克风，你还会发现发射器可能会失真. 您需要调整输入修剪. This is one strategy many people either don’t know about or simply don’t like to fiddle with. But in theater productions, we do this a lot because we match a microphone to a performer. 无论是手持，lavaliere，或仪器发射机，它将有一个输入修剪. 例如，在森海塞尔 wireless lav system, you go into the menu to access the sensitivity of the microphone (图2), and you can bring it down or bring it up depending on what your situation requires.

图2. 森海塞尔无线发射器的灵敏度调整

If you’re working with a performer or presenter who’s going to sing or speak on stage, 你得把发射机的增益调到他或她的声音上. 如果你要把麦克风夹在小号上, 你需要用不同的方式设置它.

如果你在调整吉他的输入装饰, 该设置将根据麦克风的使用方式而有所不同, whether you’re attaching an acoustic microphone or jacking into the guitar directly, 就像电吉他一样. You need to adjust the sensitivity of the transmitter appropriately; otherwise, it can distort right away and there’s absolutely nothing you can do to fix it down the line.

要调整输入微调，请让演示者/表演者以正常音调说话或唱歌. If the level starts to bounce a little bit while the person is talking or singing, that’s good. If it sits, or if it just goes up and hits the top of the audio level indicator, it’s too loud. 如果他们在说话，灯不亮, 之后你必须增加很多增益，这样你就会提高噪音底限，发出嘶嘶声. 同样的原理也适用于乐器麦克风. Have the performers play they way they will during the performance and set the transmitter’s input levels accordingly.

应对嗡嗡声

音频的另一个恼人问题是嗡嗡声. 通常是60Hz(在美国).S.交流电源发出的嗡嗡声. It comes when the ground used for the audio is coupled to different things in different places. 发生这种情况, 例如, when the venue is mixing sound behind the stage and run a couple mic lines to you at the back of the house, and you’re also plugged into a circuit that’s not grounded in the same way the house audio is. 突然，60Hz的嗡嗡声突然出现，侵入了一切. 如果你插进去的时候能听到, 甚至是触摸, 长音频线进入你的混音器, 只要你把它们拿掉，它就会消失, 你找到了问题所在.

首先要尝试的是地面升降机适配器. 你的工具箱里至少应该有一种, 因为他们可以帮助你解决很多不同的问题. That said, it’s a temporary fix, and not one you should rely on in a permanent setup.

If a ground lift adapter doesn’t solve the problem, try to work on the audio cables themselves. 有多种方法可以做到这一点. Simple accessories such as an XLR adapter can be put inline on the XLR cables to try and find which pin is carrying the offending voltage. 另外, there are more substantial transformer devices that completely isolate the in and out, 同时仍然传递音频. 这些设备通常可以解决最顽固的嗡嗡声问题.

最后，确保电源线没有和音频线一起被粘住. 这也是捕捉额外噪音的好方法. 它们之间至少要隔几英寸，如果不是一英尺的话.

射频噪声

If you’re still working with old 700mHz wireless microphones on frequencies that have been allocated for other uses—including public service—you should replace these systems as soon as possible.

如果你已经转向使用批准频率范围的系统, 你不太可能遇到干扰, 但在某些情况下也会发生. 例如, if you’re filming a lecturer who has his lav belt pack just a few inches from his cellphone, 他的手机就会受到射频干扰. 他需要把它放在讲台上，或者桌子上. 手机离麦克风越远，对信号的影响就越小.

你自己的船员也是一样. Don’t put your phone on the audio mixer, even if you’re using it to play music into your system. 射频噪声可以进入信号路径的任何部分.

过调混频器输入

Another problem that arises frequently when you’re mixing audio for live events is overmodulation (or overmod) on the mixer input. Several factors can cause overmodulation, some easy to avoid, others a bit more subtle. 首先，如果你是线电平输入，不要把它插入麦克风插孔. 它会变形. 一些混频器有一个普遍的增益，你可以拨下来，以避免剪辑. If yours doesn’t, you’ll need an external PAD to knock the line level XLR down to mic level. 这些应该在你的工具包中，并始终保持音频混音器.

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