Another feature of most mixing desks is multiple outputs. Most have a headphones output, as well as a master output, a control room or monitoring output, and possibly others. This flexibility allows you to do a number of things. You can listen to, or monitor, your audio in a number of ways. You can connect a pair of speakers to your mixing desk or use headphones. You can connect a recording device to your mixing desk if you want to record your podcast on a device other than your workstation. Mixing desks provide you with the flexibility to do just about anything you want with your audio.
Mixing desks offer these features as well:
- Phantom power: Condenser mics require phantom power to operate.
- Level adjustment: You can adjust the level of each source.
- Equalization (EQ): You can adjust the tone of each input to optimize the sound.
- Stereo panning: You can move inputs from side to side in your stereo mix.
- Effects sends: You can add special effects to your mix such as echo and reverb.
If you're going to be doing any sort of live recording, you should buy a mixing desk. The flexibility it provides is invaluable. Another reason to consider buying a mixing desk is the microphone inputs (also known as mic pre's, short for microphone pre-amplifiers). Microphones produce a lowlevel signal that must be amplified considerably. Cheap mic inputs (like the ones included on most soundcards) add a significant amount of noise during the amplification process. Mixing desks have much higher quality mic inputs, so they produce much higher quality signals. In fact, mic input quality is usually the distinguishing factor of a mixing desk.
Mixing desks come in all shapes and sizes, from portable models that offer a few input channels, to broadcast consoles that require special stands. A desktop mixing desk is probably most appropriate for podcasting. Be sure to buy a mixing desk that has more inputs than you need; people tend to "grow into" their mixing desks. After you realize that you can leave everything connected, you'll find yourself connecting everything to your mixer.
One of the latest developments in mixing desk technology has been the addition of USB and FireWire outputs. These new outputs enable you to connect the mixing desk directly to your workstation, without having to use an external audio interface or a soundcard. These are incredibly handy, because you'll have one less piece of equipment to buy (or worry about). Many mixing desk manufacturers are coming out with USB and FireWire models. In general, the FireWire models are slightly more expensive, because they enable higher sampling rates and bit depths. A couple of models are illustrated in Figure 1.
Monitoring (headphones and speakers)
When producing high-quality audio, you should know that what you're hearing is accurate. It's worth investing in a good pair of speakers, which are called monitors in the broadcast world. You'll also need a good set of headphones to be able to monitor while you're recording to avoid feedback (which is explained in the "Feedback: What It Is and How to Avoid It" sidebar).
Headphones can be either closed back or open back. Open back headphones tend to be lighter and more comfortable, but the design has a couple of potential shortcomings. First, outside noise can come in via the open back, so they're not good for noisy environments. Second, if the headphone volume is turned up too loud, the sound coming out of the back may be picked up by nearby microphones. This is known as bleed. It's usually not too much of a problem with spoken presentations, because headphone volume tends to be low and the bleed minimal. It can be a factor when recording live music, however, which tends to be monitored at much greater levels. Closed back headphones are best for noisy environments, because they allow less outside noise to reach your ear, and less headphone noise leaks out.
A number of specialized headphones are available. Most portable players come with in-ear headphones. In-ear headphones offer excellent isolation because they're so close to the ear drum; some are even custom molded to the ear canal. This is a double edged-sword, though. Anything that close to your ear drum has the potential to do lots of damage. Noise-canceling headphones use sophisticated circuitry to minimize ambient noise such as the whine of an airplane engine. Wireless headphones send the audio signal via a wireless technology such as Bluetooth or UHF. For critical listening, use a good pair of wired headphones. They're less susceptible to interference, and they don't have any fancy circuitry messing up your audio. A couple of standard broadcast headphone models are shown in Figure 2.
Although you can do all your podcast production with a good set of headphones, you'll also probably want to invest in a good set of monitors. Headphones can be fatiguing, and they have an exaggerated sense of stereo separation. You should always check your mixes on a set of monitors. Remember that a good portion of your audience will be listening at their desktop computers, so you should make sure their experience is going to be good. Granted, your audience may be listening on cheap plastic speakers that came with their "multimedia-enabled" computers. That's no excuse for you to produce using the same equipment. Producing your audio to the highest possible quality requires accurate monitoring.
Monitors are probably the most contentious piece of audio equipment you'll buy, because judging the quality of a pair of monitors is very subjective. You'll see all sorts of jargon tossed around on manufacturers' Web sites, along with frequency response diagrams and rave reviews from audio engineers. Generally, the more you spend, the more accurate the monitor. Also, because low frequencies are particularly difficult to reproduce accurately, more expensive monitors have better low frequency reproduction. Many desktop multimedia speaker systems use subwoofers to reproduce the low frequencies. These are fine, provided the subwoofer doesn't color the sound too much.
One thing you should definitely consider is whether the monitors are shielded. Shielded monitors are built so that they don't pick up interference from video monitors, which can be a problem. You also may want to buy active speakers, which have amplification built in, so they don't require a separate amplifier. Many professional monitor manufacturers exist, and each has a wide selection of monitors. A few examples are shown in Figure 3. Choose monitors that fit your budget and sound good to you.
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