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Mixers and Preamps
One of the choices you need to make is whether to buy a mixer and/or stand-alone preamps. There are advantages either way.
What are Preamps?
A preamp is used to boost the signal from a microphone or musical instrument so that it can drive the input of the audio interface. The input of the audio interface is a "Line Level" input and is designed to match the output level of rack mount gear, mixers and preamps. A Line Level signal is much "hotter" than a signal that comes from a microphone or musical instrument such as an electric guitar
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| M-Audio Audio Buddy | M-Audio DMP3 |
Preamps can be stand-alone, or they can be integrated into a mixer. Stand-alone preamps such as the m-Audio Audio Buddy have two channels and sell for less than a hundred dollars. These preamps are generally as good or better than the preamps that come built-in with lower cost mixers. This option also gives you the choice of having a variety of preamps. However, preamps can be very expensive, and you may not necessarily save money by buying stand-alone preamps verses a single mixer.
Many preamps and mixers have two kinds of inputs. One is the microphone input and the other is the DI (Direct Injection) input. DI is intended for matching music instruments to a line level input. These inputs are frequently used for bass guitars and synthesizers.
What is a Mixer?
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Mackie 1202 VLZ Pro |
The mixer performs two jobs. One is to provide microphone preamps. A mixer usually has a number of inputs that have preamps built in. These inputs are called microphone inputs. If you have a mixer that has enough microphone inputs, you won't need stand-alone preamps. |
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Mic. Inputs |
The second job of the mixer is to provide a monitor mix. The monitor mix is a stereo mix of each of the instruments that is currently being recorded and maybe even some instruments that are not being recorded. Previously recorded tracks can be added to this mix. The monitor mix is then played through the speakers and or headphones. Musicians listen to this mix through headphones while they are being recorded. |
Should I Choose a Preamp or a Mixer?
Since most recording software has a mixer built in, you can pass on the mixer and just buy preamps instead. However, when it comes to setting up my monitor mix, I like to have a real mixer that I can access quickly. Using a software mixer can be too cumbersome. Also, with an outboard mixer, you do not have any digital latency that can occur when using a software mixer. Latency is a delay that occurs between the input and output of your audio interface. This delay can be long enough to cause timing problems in your recordings.
Software Mixer in Cubase VST
I use a combination of a small mixer and stand-alone preamps. I started out with a 12-channel mixer and a 4-channel audio interface. This combination was excellent. Later I moved up to an 8-channel audio interface. To use the four new channels, I had to buy either a larger mixer that had eight microphone inputs or four channels of preamps. I chose the preamps because I wanted the option to experiment with a variety of preamps.
My recommendation for someone starting out would be to pick up a 12, 16 or 20 channel mixer. Mixers made by Mackie, Behringer, Soundcraft and Heath and Allen all have microphone inputs that will easily do the job. Later you can purchase some outboard preamps and move up to a higher grade signal chain. If you are using outboard preamps, the quality of the mixer will have no effect on your recording since you will only be using it for the monitor mix.
On most of the smaller mixers, only some of the channels have microphone inputs. For instance, the Mackie 1202 VLZ has twelve channels total, but only the first four channels have microphone inputs. The remaining channels are line level inputs. When you are using a 4-channel audio interface, this size of mixer is a good choice, but if you plan to use an 8-channel audio interface, you may want to look for a larger mixer that has at least eight microphone inputs.
In many mixers, some channels are stereo. The manufacturers count these as two channels. I suppose that's fair, but it's misleading too. For instance, the Mackie 1202 is called a 12-channel mixer. It has four mono microphone inputs and four stereo line level inputs. Each stereo input has only one set of controls, so if you are working with mono sources, this really is more like an 8 channel mixer.
Example:
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Here is an example of using a mixer to record drums. In this example, we have a 12-channel mixer with four microphone inputs and four stereo inputs. The drums are connected to the microphone inputs of the mixer. The amplified signal then goes directly to the audio interface card. The four microphone inputs are also mixed down to stereo in the main bus. That signal is sent through the "main outs" to the monitor speakers and headphones. You should also connect output channels 1 and 2 of the sound card
into the Tape inputs of the mixer. This way when you are dubbing
in new tracks, you will be able to hear the existing tracks along
with the monitor mix. |
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Without the band to play along with, it can be difficultto keep track of where you are in the song. Band members usually need to hear the whole band playing while they record their parts. When recording drums, use the remaining four channels of the mixer for the other instruments and vocals. These will not be recorded but will appear in the monitor mix along with the drums. Since the remaining four inputs are line level, you must send the microphone and instruments through preamps first. Of course, when you are doing this, you will want to isolate the drums from the other instruments and vocals so that they do not end up on the drum tracks |
Connecting a Mixer to the Audio Interface
We need to get the boosted signal from the mixer to the audio interface. The larger mixers have direct outs. There is one for each input that has a microphone preamp built in. You can easily identify these inputs on your mixer because they are the inputs with the XLR input jack. The smaller mixers such as the Mackie don't have true direct outs. However, you can use the Insert jack as a direct out. The two disadvantages of this are that you lose the use of your Insert jack to insert effects. The other limitation is that the signal from the Insert jack is unbalanced. Usually, the better mixers will have direct outs that are balanced. For most home studios this should not be be a problem unless your mixer is more than 12 feet from your audio interface. For short distances, unbalanced cables will work just as well as balanced ones, so save your money and use unbalanced cables.
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This setup means that you lose the use of the Insert jack to insert your effects. The fact is, you can simply run the signal from your Insert jack to your effects unit, most likely in this case, a compressor. Then run the output of the compressor to the input of your audio interface. The disadvantage of this is that you won't hear the effect of your compressor in the monitor mix. To solve this, connect the effects in the Insert jack just as you normally would, except, at the output of the last effect, split the signal with a Y connector. Feed one signal back to the Insert jack and feed the other signal to the audio interface card. |
Adjusting Levels of Preamps and Mixers.
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Mixer VU Meter |
Before you record, make sure that your mixer or preamp is level matched to your audio interface. It doesn't have to be exact and probably won't be. Ideally, when the VU meter on your mixer or preamp reads zero db, the software VU meter in your computer should also read zero db. Zero db is the point where the signal begins to clip. When you are recording, you will actually use the software VU meter in the recording program. The software meter actually shows the level of the signal at the input of your audio interface. If your preamp VU meter reading is a little higher than 0db when your software VU reads 0 db, it's not a problem. This is because your preamp will have some "headroom" above 0 db before it starts clipping. |
If your preamp starts to clip before the software meter, you need to change the sensitivity of your audio interface. The most common setting is -10dBV. Some audio interfaces have two settings, -10dBV and +4 dBu. Many audio interfaces have a variable sensitivity control. Simply set this level for a 0 db reading when your preamp reads 0 db.
To adjust the level of your preamp, simply adjust the microphone input gain control so that your software meter is just below the point where it clips. This should provide you with the best recorded signal. Of course you want to make sure that at no time during the recording the software meter never reaches 0 db. If it does, you will have a clipped signal that will not sound very pretty.
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Adjusting a mixer is much like adjusting a preamp except that you have two levels to adjust. First you adjust the microphone input gain just like the preamp. This control is sometimes referred to as trim. To adjust the microphone input gain, follow the same procedure as adjusting a preamp. |
Trim ( Mic. Gain ) Controls|
Fader Controls (Channel gain for monitoring) |
The second control is the fader. It is used to adjust the level the channel will produce in the monitor mix. This will have no effect on the record level; however, the gain control affects both, so you need to set the gain first. Do this for each channel being recorded. |
Monitoring a Preamp Using Software Monitoring.
When using a preamp instead of a mixer, monitor mix is controlled by the software mixer in your audio recording program or sequencer. You may need to configure your program for monitoring. This will depend on the particular software and hardware you are using. Keep in mind, for this to work well, your latency will need to be below 10 msec. This delay will end up in your recording, so it must be kept to a minimum. 1 or 2 msecs is good. Another option is to use Direct Monitoring. This is a low latency monitoring mode provided by your hardware. There are two disadvantages to this. Some audio interfaces do not allow you to control the monitor levels. If this is the case with your card, I recommend you don't use Direct Monitoring. The second problem is that it won't allow you to hear the results of the effects plug-ins that you are currently using on that channel. I don't really consider this a big problem. You shouldn't be using effects during tracking anyway. If latency turns out to be an issue with your combination of audio interface, computer, and software, I highly recommend buying an inexpensive mixer for your monitoring.
Monitoring a Preamp Using a Mixer.
If you will be using outboard preamps and a mixer, it is simple to set them up so you can hear your preamp output in your monitor mix. Using a Y connector, you simply split the signal from the preamp's output and run one cable to your audio interface and the other one to a line level input of your mixer. This is the approach that I use.
Entire contents Copyright © 2003 by Kevin Kemp, all rights reserved.