How to Master Audio Mixing for Live Production and Streaming
Live audio is challenging. Unlike many of the issues that arise on the video side of the equation, none of the problems that affect audio quality—RF interference, feedback, ground loop hum, hiss, over-modulation—can be seen. 所有这些挑战都需要对问题的了解和理解，才能正确地评估和解决问题. On live productions, more often than not, the time to fix audio issues is as soon as you hear them starting to happen.
You might find yourself dealing with over-modulation on the input to the mixer, or bad equalization in your mixer. Your potentiometer or fader might be too high or too low, and you’ll find yourself trying to compensate for it later in the mixer. 或者你的母带音频可能会失真，这意味着你需要试着把它压下来.
Finally, there’s the dreaded feedback. 你可以通过掌握一个好的混音器的控制和功能来解决这些问题(Figure 1, opposite page), or— better yet—instructing presenters, talent, 以及其他船员如何正确使用他们手中的技术，这样他们就能给你发送一个干净可用的信号.
Figure 1. The Behringer Eurorack UB1222FX-PRO professional audio mixer.
Microphone Placement
你可以做的最重要的事情之一，以确保良好的音频是适当的麦克风放置. For example, you can use a good lavaliere microphone on the body of the speaker, as opposed to a podium microphone he or she can walk away from, or a handheld microphone that he or she can wave around the air. You might even try a headset microphone if the venue is particularly noisy. 在情况允许的情况下，这些做法变得更加谨慎，也更被社会所接受.
Also, be sure your source audio won’t overwhelm your microphone. Usually, this happens with music, for instance, 当你的表演者使用人声麦克风为鼓或口琴和音频失真在麦克风. But it can also happen if you set up a microphone for someone who speaks softly, then hand it to a football coach who shouts everything to the back of the room. 你可以调整无线麦克风的输入电平，这样它就能接收到良好的信号, but does not overmodulate.
With handheld mics, the as-near-the-mouth-as-possible rule applies. If you ever do weddings or other events, watch the DJ. DJs know how to work a microphone. DJ可能会站在扬声器前面——这通常会引起反馈——但要把麦克风拿得离他或她的嘴非常近，以避免说话声音太大. The system will also be set so that unless the microphone goes into the speaker, it’s not going to create feedback.
说到乐器麦克风，自然，最好的方法是把麦克风放在乐器上. On some productions you could encounter, say, an acoustic guitarist who wants to play to a mic on a stand. That’s a lot farther from the instrument than an on-instrument guitar mic, which will pick up the strings and the resonance of the chamber, 并且给你在其他环节更好的回旋余地来避免反馈和其他问题.
在这些领域，有效的麦克风放置和积极的麦克风引导可以使你捕获和传递的音频质量有很大的不同.
Overwhelming Source Audio
在音频录制问题出现的情况下，源音频压倒麦克风在使用, 首先要检查的是麦克风的声压级(SPL). Microphones have sound pressure level ratings, which vary depending on the type of microphone, the manufacturer of the microphone, and the size of the microphone.
One microphone that a lot of people use is the Shure SM-58. 这是一个经典的人声麦克风，适合某些任务，但不适合其他任务. For instance, the SM-58 has an SPL rating of 94dB. To put that in perspective, 一些常见的近似声压级包括飞机起飞时的110dB, or 100dB for a rock concert. 如果你正在使用SM-58在现场活动，并记录一个响亮的乐器，如踢鼓或喇叭喇叭直接进入它, that sound can easily overwhelm this mic and distort the audio.
With wireless mics, you’ll also find potential for distortion in the transmitter. You’ll need to adjust the input trim. 这是一种很多人要么不知道，要么就是不喜欢摆弄的策略. 但在戏剧制作中，我们经常这样做，因为我们将麦克风与表演者相匹配. Whether handheld, lavaliere, or instrument transmitter, it will have an input trim. For instance, on the Sennheiser 无线lav系统，你进入菜单访问麦克风的灵敏度(Figure 2)，根据你的情况需要，你可以把它降低或提高.
Figure 2. Sensitivity adjustments on Sennheiser wireless transmitters
如果你和一个将要在舞台上唱歌或讲话的表演者或主持人一起工作, you’ll need to adjust the gain of the transmitter to his or her voice. If you’re going to clip that microphone to the horn of a trumpet, you’re going to need to set it differently.
If you’re adjusting input trim for a guitar, the setting will vary depending on how the microphone is used, 无论你是连接一个声学麦克风还是直接插入吉他, as with an electric guitar. You need to adjust the sensitivity of the transmitter appropriately; otherwise, 它可以马上扭曲，你绝对无法做任何事情来修复它.
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. 如果关卡在玩家说话或唱歌时开始有一点跳跃，那就很好了. 如果它静止不动，或者它只是上升并击中音频电平指示器的顶部，那么它就太大声了. If they’re talking and it doesn’t light up, you’ll have to add so much gain later that you’ll raise the noise floor and hiss. The same principle applies to instrument mics. 在表演过程中，表演者是否按照自己的方式演奏，并相应地设置发射机的输入电平.
Dealing With Hum
Another very annoying problem with audio is hum. Usually it’s a 60Hz (in the U.S.) hum from AC power. 当用于音频的地面在不同的地方耦合到不同的东西时，它就出现了. This happens, for instance, 当场地在舞台后面混音时，在房子后面给你放几根麦克风线, 而且你还被插入了一个电路，这个电路不像家里的音响那样接地. Suddenly, the 60Hz hum crops up and invades everything. If you hear it when you plug in, or even touch, the long audio lines into your mixer, and it goes away as soon as you remove them, you’ve pinpointed the problem.
The first thing to try is a ground lift adapter. You should always have at least one of these in your kit, because they can help you solve so many different problems. 也就是说，这是一个临时的解决方案，而不是一个你应该依赖的永久设置.
如果地面升降机适配器不能解决问题，请尝试在音频电缆上自己工作. There are multiple ways of doing this. 简单的附件，如XLR适配器，可以在XLR电缆上插入，试图找到哪个引脚携带了有害的电压. Alternatively, 有更实质性的变压器装置，完全隔离的输入和输出, while still passing audio. These devices can usually resolve the most stubborn hum problems.
Lastly, make sure power cables aren’t taped down along with the audio cables. That’s also a great way to pick up extra noise. They should be separated by at least a few inches if not a foot.
RF Noise
如果你还在使用旧的700mHz无线麦克风，而这个频率已经被分配给其他用途——包括公共服务——你应该尽快更换这些系统.
If you’ve moved on to systems that use approved frequency ranges, you’re less likely to encounter interference, but it can still happen under certain circumstances. For example, 如果你正在拍摄一个讲师，他的腰带包离他的手机只有几英寸远, you’re going to get RF interference from his phone. He needs to leave it on the podium, or on a table. The farther the phone is from the microphone, the less it will affect your signal.
The same goes for your own crew. 不要把你的手机放在混音器上，即使你用它来播放音乐. The RF noise can get into any part of the signal path.
Overmodulated Mixer Input
另一个经常出现的问题是混音器输入上的过调制(或过模). 有几个因素会导致过度调制，有些很容易避免，有些则比较微妙. To begin, if you’re feeding line-level input, don’t plug it into the mic jack. It will distort. Some mixers have a universal gain that you can dial down to avoid clipping. 如果你的没有，你需要一个外部PAD将线电平XLR降低到麦克风电平. These should be in your kit and always stay with the audio mixer.
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