Digital Home Recording

Mixers

Getting Sound into a Mixer
Getting Sound out of a Mixer

Getting Sound into a Mixer by Marc Schonbrun

Getting sound into a mixer properly is very important, and it's easy to make mistakes here. Start with the microphone channels. Attach your microphones to the microphone channels on the board. If your microphones are condenser microphones that require phantom power and your mixer supports it, flip the switch on the top or side of the unit that supplies phantom power. Now your microphones will be powered up and ready to go. Next, connect your line-level equipment, such as keyboards and line outputs from amplifiers and direct boxes.

Setting Recording-Friendly Levels

You need to set the level of each input you record through the mixer. Activate the solo button on the channel you are working on to isolate the sound. For microphones, set the input trim control so the microphone's loudest sounds do not clip the input. If your mixer has a meter that lights up (most do), make sure the loudest sound stays in the green lights and doesn't hit the red. Repeat this step for each microphone you have.

When you set the microphone levels to record a drummer, make sure the drummer hits the drum really loud so you can get an idea of when clipping might occur. Set your gain so that even the loudest hit does not clip.

Line-level instruments connect to the line channels. You should adjust the gain on the keyboard or guitar amplifier, not on the recorder. The fader for those tracks should be set to “unity gain,” which means nothing added, nothing subtracted. Unity gain is marked with a zero. This allows you room in either direction for volume changes later on. Also, check the level meter to make sure you aren't clipping. Taking time to check settings now will ensure that you don't clip and distort the inputs while you're recording.

Measuring Electrical Voltage

“Decibel” is a confusing term. Scientifically, the decibel is not a concrete measure of any one thing; it's a ratio of power or intensity to other factors. There are actually a bunch of different decibels that we deal with. The basic decibel measures sound pressure or the loudness of the sound pressure created. For instance, the sound of a subway car about 200 feet away is 95dB.

On a mixer, decibels are used in a much different way. The first way is as a measure of electrical voltage; the second way is as a level of sound output. When you look at a mixer's slider, you will see that it's marked up and down with decibel marks, ranging from negative decibels to positive decibels. See Figure 10-5.

Negative decibels? This seems to go against what we know of decibels. If you're comparing a volume slider to sound pressure, you will be confused. Think of the volume slider simply as a way of boosting or lowering the prerecorded signal. Negative dB values mean you are reducing the level that's been recorded, and positive dB values mean you are raising the recorded output.

So, as you mix, place all of your volume sliders at zero. At that setting the mixer is not artificially boosting or cutting anything. You hear the signal that you recorded from the instrument or microphone itself.

Figure 10-5: Mixer levels

Maximize Music, Minimize Noise

We've talked about setting levels high enough so that they are full and don't clip. This is because the louder the input signal, the less noise the signal will contain. Even if you are planning on using a soft track, record the input at a high level. Turning the track down later will help cover up any noise in the signal. Volume faders on mixers or computers can boost only a few decibels. They can, however, reduce signals to nothing. It's better to start with too much signal and reduce it later than to have too little signal and try to overboost.

Every signal, no matter how well recorded, will include some noise. This isn't usually a problem if you set the correct signal-to-noise ratio by recording tracks properly and setting the correct input levels. If the signal is loud enough, the noise won't be an issue if you've paid attention to your settings.

Output Scale

More decibel madness! When we discuss using faders to boost and cut input volume, we might naturally push the vocals +2dB to make them louder; increases in dB results in louder signal. Here's where the other side of the decibel confusion erupts, because when it comes to final output, decibels are measured using an entirely different system. We're now faced with a system called decibel full scale (dBFS). Decibel full scale simply considers 0dB as the absolute loudest signal you can have. Since decibels aren't a fixed ratio, dBFS calls 0 the loudest and works backward. When recording, mixing or mastering music, especially in the digital world, you can never exceed 0dBFS, ever. If you do, you will distort and clip the signal. Thankfully, you have meters that show you how loud you are. Meters even glow red when you've clipped.