For the purposes of this example, we'll assume that you're using a microphone and a mixing desk, a USB audio interface, and recording straight to your hard drive. Your audio setup may differ slightly, but you should be able to follow these steps regardless:
1. Connect your microphone to your mixing desk, your mixing desk to your USB interface, and your USB interface to your computer. You should be using balanced cables whenever possible, because they provide a solid connection point and are highly noise-resistant. Turn on your mixing desk. If you're using a condenser microphone, be sure to turn phantom power on (or you won't hear a thing).
Tip : Be sure to turn on phantom power after you've connected all your microphones. Some microphones may be damaged if you plug them in with the phantom power already turned on.
2. Make sure you're monitoring only the microphone channel. Some mixing desks have "Solo" buttons to accomplish this; if your mixing desk doesn't have a solo button, then make sure all the other channels are turned down.
3. First, set the input level of the microphone. Do this by adjusting the input level (or trim) knob at the top of the mixing desk channel your microphone is plugged into, as shown in Figure 1. Speak into your microphone, and adjust the input level. The Mackie Onyx 1220 uses a peak meter, so adjust until it is peaking at -6dB to -3dB. A few peaks over zero are okay.
4. To set the output level of the mixing desk, take the channel out of solo mode if your desk has a solo button. The meters on the mixing desk will now show the level of all channels combined. Turn your microphone channel up to 0dB (on some desks this is marked "U" for unity gain).
5. Mixing desks allow you to move things from side to side in the mix. This is known as panning, and is controlled by the pan knob on your mixer. Each channel has a separate pan control. Make sure your microphone is in the center of your mix. Check the pan setting to make sure it's right in the middle. Sometimes conversations between two people can sound more intimate if the two speakers are panned slightly to the left and right, but most of the time — and especially when setting up your gain structure — all microphones should be right in the middle of your mix.
Tip When recording an interview between two people, it's tempting to pan one person hard left and the other hard right. That may sound cool at first, but it isn't. It ends up sounding like ping-pong, where the voices are jumping from one speaker to the other. If your listeners are using headphones, you'll drive them absolutely crazy. A little separation is fine, but don't go overboard. And remember that if you're using stereo for separation, you're going to have to encode in stereo, which requires a higher bit rate to sound good.
6. Adjust the final output of your mixing desk by adjusting the master volume. This is generally on the lower left of the mixing desk, below the meters. You should set the output meters to -6dB to -3dB, leaving a bit of headroom for the unexpected.
7. Next it's time to move on to the USB audio interface. Depending on the make and model, you'll have some sort of meters and some sort of input adjustment. On some models, the metering can be fairly rudimentary. Adjust to keep your level consistent with the output level of the mixing desk. If you don't have full meters on your USB interface, you can use your recording software to check your input level. Open your audio editing software. You may need to put it in record mode to get to the level meters. Make sure your level is in the -10dB to -6dB range, and remember that anything over zero will distort!
Note Some USB audio interfaces come with special software to adjust the input level. If so, use this software to set your levels. After you've set the level via the software application, the level is automatically set for your audio editing software.
Congratulations. You've just set up your gain structure. Each piece of equipment is operating in its optimal range, so you should be producing a high-quality, noise-free audio signal. The best part about setting up a gain structure is that after you've set it, you shouldn't have to worry about it anymore. You can make small adjustments if necessary using the channel adjustments or the master volume output of your mixing desk.
Tip If you're connecting a number of different audio sources to your mixing desk, label the channels so you know what is coming in on the channels. Some mixing desks have an area to do this, known as a channel strip. If your desk doesn't have a channel strip, you can always create one by stretching a strip of masking tape below the channel faders (or knobs). Then you can write on the masking tape. Believe me, when you're grabbing for a fader in the middle of a podcast recording, knowing which fader is the right one is critical.
If you have more microphones or more equipment that you want to use during your podcast, you should set the input level for each channel just as we did for the microphone channel in the previous example. You can adjust the relative volume for each channel as needed using the channel level adjustments, so that all your inputs are mixed together at the right levels. Now that your levels have been set, you need to learn a little about digital audio.
Caution Make sure you always plug microphones into mic inputs and line level equipment such as CD players and iPod headphone outputs into line level inputs. Most inputs are clearly labeled as one or the other or have a switch that determines the expected input level. If you plug a microphone into a line level input, you won't get enough gain. Conversely, a line level output distorts a microphone input. Just because a cable fits doesn't mean it's the right input!
Understanding digital audio
At some point, your audio is going to have to be digitized on the way to becoming a podcast. Digitizing is the process of converting an analog audio input into a digital audio file. Whether you're recording directly to your hard drive or you're using a digital recording device, you have to choose which digitization settings to use.
To fully understand what is involved in digitization, understanding how digital audio files are created is important. Figure 6.3 illustrates an audio signal. The audio signal starts off as a continuously changing voltage. This voltage is created by the vibrations of the diaphragm inside a microphone and is what eventually causes the cones inside a speaker to vibrate and reproduce the original sound.
To store this as a digital audio file, we take measurements of the wave at specific intervals. These measurements are known as samples. In Figure 2, each section of the wave has different numbers of samples under it. The number and accuracy of these samples determine how accurate the digital version of our audio file is and therefore the fidelity of the digital version to the original.
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