by Ethan Winer

This article first appeared in the March 2003 issue of EQ magazine

One of the most frequent questions I see in the audio newsgroups asks how to connect a mixer to a computer-based recording setup. Many people have a small mixer, like the Mackie 1402, and want to record basic tracks first and then add overdubs later. The Mackie manuals show several setups for combining musical instruments and other sources to play them through loudspeakers. But they ignore what may be the most common setup of all - a typical digital audio workstation (DAW). This article explains the basic principles of recording in a DAW and shows the best way to connect the various components through a small mixer. I will use the Mackie 1402 VLZ for these examples, but the concepts apply to any mixer that offers an insert point for each preamp output.

With most DAW setups, it's best to record each instrument and microphone on a separate track. This gives the most flexibility when mixing, letting you change the volume and equalization separately for each sound source, add more or less reverb to just that instrument, and so forth. I also suggest that you do all mixing within the DAW program using the software's volume, pan, and plug-in effects, rather than sending individual tracks to a hardware mixer. Mixing in a DAW is more flexible because it allows the mix to be automated and recalled exactly. It also ensures that when you export the song to a stereo Wave file, it will sound the same as what you heard while mixing.

INPUTS AND OUTPUTS

Most small mixers contain two independent sections: an input section and a mixer section. The input section contains the input connectors (XLR and 1/4-inch) and the preamps, which raise the small input signals to line level so they're suitable for recording. The mixer section then combines all of the preamplified inputs into one stereo mix that you can play through loudspeakers or headphones. It's important to understand the difference between the input channels, which are available independently, and the combined stereo mix. You'll record each sound source through the preamps to a separate input of your sound card, but you also need to monitor all the channels mixed together to hear yourself as you play or sing, and to hear the tracks already recorded.

The first step is to route each microphone or instrument to a separate input on the sound card. If you have only one stereo sound card, you can record only one stereo source at a time, or optionally two mono sources. (Of course, you can record any number of additional tracks later as overdubs.) If you have a multi-channel sound card, you can record as many separate tracks as the sound card has inputs. However, you should play all tracks through one output, even if your sound card has several outputs. This way the mix is controlled entirely by the settings in your DAW program, independent of the knobs on the hardware mixer.

Figure 1: The 1402's Front Panel Input Section

Figure 1 shows the input section of a Mackie 1402 VLZ mixer. You can connect either XLR microphone or 1/4-inch instrument cables, which go through the 1402's preamps and then to the mixer section that combines the inputs. The channel insert portion of the 1402 back panel is shown in Figure 2 below, and this is where you'll connect each preamp output to one input of your sound card. The original purpose of an insert point was to insert a hardware effect box, such as a compressor, into the recording chain. But with a DAW, you can do that with plug-ins later. For our purposes, the insert point will serve as a splitter to send the preamplified input to the sound card while also sending it to the rest of the mixer for monitoring. When an output is taken from the insert point, it's called a direct out because the signal is taken directly from the output of the preamp, before passing through the mixer's volume and tone control circuits.

Figure 2: The 1402's Back Panel Insert Points

With nothing plugged into an insert jack, the output of the preamp goes through the channel volume, pan, and EQ controls on the front panel and is combined in the mixer section with the other preamp outputs. But when you insert a 1/4-inch plug only partway into the jack, the output of the preamp is sent to the inserted plug and also goes to the rest of the mixer. This is the key to recording each source to a separate track. Since the preamp output still goes to the mixer section, you can control how loudly you hear the source through your speakers with that channel's volume slider. And since each preamp output goes directly to the sound card, it's the only thing recorded on that track. If you were to record from the mixer's main output, the new recording would include all the tracks already recorded as well as inputs intended for other tracks.

Figure 3: Connecting it all together - be sure to push the plugs only partway into the insert point jacks!

Figure 3 shows how each channel's insert point output goes to one input of the sound card. The sound card's main stereo output then goes to one of the mixer's stereo inputs so you can hear your recording program's playback. This way you can control the volume you hear for each track being recorded with its input channel volume slider, and control the playback volume of tracks already recorded with the stereo channel's slider. In this example, mixer channels 1 through 6 control how loudly you hear each source being recorded, and stereo input pair 13-14 controls how loudly you hear the tracks already recorded.

SETTING RECORD LEVELS

Each of the six input channels has two volume controls: the preamp gain knob (also called Trim) and the channel volume slider. Both affect the volume you hear through the loudspeakers, but only the preamp gain changes the recording level sent to your sound card. Therefore, when recording, you must first use the preamp gain control to set a suitable recording level, then adjust the channel slider for a comfortable volume through the loudspeakers or headphones. Since the channel volume slider and equalizer are not in the path from preamp to sound card, you can freely change them without affecting the recording.

MONITORING WITH EFFECTS

It's often nice to hear a little reverb when recording yourself singing or playing, for extra inspiration and to get a sense of how it will sound in the final mix. Many DAW programs let you monitor with reverb and other software effects while recording, but I usually don't recommend that. One problem with monitoring with effects is the inherent delay through the program and plug-ins, especially with slower computers. Another problem is that the effects tax the computer more than recording alone. If your computer can just barely record eight tracks at once and you monitor with effects while recording, you may end up with gaps in the recorded audio or the program might stop suddenly. Fortunately, most small mixers, like the 1402, have Aux busses where you can patch in a hardware reverb. Any reverb you apply on an Aux buss affects only the monitoring path and is not recorded. Therefore, you can hear yourself sing (using earphones) with all the glory of a huge auditorium, and defer the amount of reverb until you make the final mix. Better, since reverb on an Aux buss is not recorded, an inexpensive unit is adequate.

Likewise, I recommend recording without EQ or compression effects. With analog tape, the hiss is always a problem; in the old days it was common to add treble boost or compression while recording if you knew those would be needed later. But modern digital recording - even at 16 bits - has a very low noise level so recording with effects is not needed. More important, it's a lot easier to experiment or change your mind later if the tracks are recorded with no processing. It's difficult to undo equalization, even if you write down exactly what you did, and it's just about impossible to remove compression! To me, one of the greatest features of DAW recording is the ability to defer all balance and tone decisions until mixdown. This feature is lost if you commit effects by writing them permanently to the tracks. The only exception is when an effect is integral to the sound, such as a phaser or echo on an electric guitar.

THE WINDOWS MIXER

Most pro-quality sound cards include a software "control panel" to set sample rates, operating levels, internal patchbay routing, and so forth. But consumer grade PC sound cards rely on the Windows mixer for level setting and input selection. You launch the Windows mixer by double-clicking the little yellow loudspeaker icon in the lower right of the screen. To get to the Record Panel screen shown in Figure 4, click the Options menu, then Properties, and under Adjust volume for, select Recording as shown in Figure 5. If you have a typical consumer sound card, you should select Line-In as the recording source and be sure to set the input level to maximum.

Figure 4: The Windows Mixer Record Panel

The Windows mixer Play Control panel (not shown) adjusts the mix of sources that play through the Line Output jack of the sound card. The Record Control panel lets you select one input from which to record. Be aware that the Windows mixer is probably hiding some input and output level controls. Yet those sources can contribute hiss from an unused input or add noise generated by the hard drive or video card. For example, you might hear scratching sounds as you move your mouse or as things change on the screen. Therefore, you should select all of the available playback sources in the Properties screen (Figure 5) to make them visible. Then mute or turn down all the sliders you are not using, such as TAD (telephone answering device), Microphone, and so forth. You can hide them again afterward if you don't want to see them.

Most Creative Labs SoundBlaster cards also have a WhatUHear input source that records the same mix of sources defined in the Play Control panel.  If you have a SoundBlaster card, do not use WhatUHear when recording audio because that will add whatever tracks you are playing along with to the current recording. It may also add hiss to the recording because it includes the MIDI synthesizer, CD Audio, and other inputs if they are not muted. The only time WhatUHear is useful is when you need to record audio from the sound card's MIDI synthesizer or convert a MIDI track that uses SoundFonts to an audio track, and you want to include the sound card's reverb in the recording. Otherwise, select MIDI as the record source and add reverb later to the audio track in your DAW program.

Figure 5: The Windows Mixer Properties

OTHER DAW ISSUES AND ADVICE

• Earlier I stated that you should push the 1/4-inch plug only partway into the insert jack so the preamp's output will go to the sound card and also to the rest of the mixer. If you insert the plug fully, the preamp's output will still go to the sound card, but the connection to the rest of the mixer is disrupted so you'll no longer hear what's being recorded. Unfortunately, these jacks are sometimes too loose to make a reliable connection when the plug is not fully seated, or they become worn over time, so you have to wiggle the plug occasionally to get the signal back. The best solution is Radio Shack's adapter 274-1520. This inexpensive gadget can be inserted fully into the mixer's insert jack, yet it retains the connection needed from the preamp to the rest of the mixer. Added August 2, 2015: This part is no longer available now that Radio Shack is out of business. You might find these adapters online by searching for "Radio Shack 274-1520" but you'll probably have to wire them up yourself as in the drawing below.

• In Figure 3 the sound card's main stereo output comes into the mixer on stereo channel 13-14. This provides a separate volume control for the DAW's output, which can be adjusted independently from the volume of each input being recorded. But you may be using all of the mixer's stereo inputs for other sources like a CD player, cassette deck, and so forth. Or maybe you have a smaller mixer like the Mackie 1202 that has fewer inputs. In that case you can connect the sound card's stereo output to the mixer's second Aux Return, if available, or even to the Tape Input. If you use the Tape Input, though, you won't have a separate volume control for the DAW program's playback.

• Even though the Windows mixer has record volume controls for each input source, it is important to set these to maximum and adjust the record level using the preamp gain on your hardware mixer. The same is true for the software control panel that's included with more expensive sound cards. Software volume controls affect the volume after the sound card's A-to-D converter. So if the level from your mixer's preamp is too high and overloads the sound card's input, reducing the software volume control just lowers the recording level yet the signal remains distorted.

• Most DAW programs let you apply plug-in effects either individually to one track, or on an Aux buss that can be shared by all tracks. In general, any effect that does something to the audio should be inserted on the track, and effects that add something to the audio should go on a buss. For example, EQ, wah, chorus, and compression effects modify the audio passing through them and should therefore be applied to a track. On the other hand, reverb and echo add new content - the echoes - and are better placed on an Aux buss. Further, reverb plug-ins use a lot of the computer's limited calculating power to generate the enormous number of echoes needed to create a realistic reverb effect. So adding separate reverb plug-ins to many tracks is wasteful. Moreover, if you use only one or two reverbs for all tracks, the result will be more coherent and sound like it was recorded in a real room, rather than in many different acoustic spaces.

• Folks who have used analog tape recorders but are new to digital recording tend to set the record levels too high. With open reel tape and cassettes, it's important to record as hot as possible to overcome tape hiss. But analog tape is more forgiving of high levels than digital systems. Analog tape distortion rises gradually as the signal level increases and becomes objectionable only when the level gets very high. Digital recorders, on the other hand, are extremely clean right up to the point of gross distortion. Therefore, I recommend aiming for an average record level around -12 dB. or even lower to reduce the chance of distortion ruining a good performance.

• If you use your DAW for both MIDI and audio, and you have a SoundBlaster Live or Audigy sound card, you need a way to record the entire final mix. You can't just tell your DAW program to render the mix as a Wave file because that would omit the MIDI instruments. One solution is to record all of the MIDI instruments at once to a new audio track, which works well and takes only as long as the song duration. To do this, arm a stereo audio track for recording, in the Windows or Creative mixer select MIDI as the record source, then start recording. When the song has finished, you'll have one stereo track with no reverb that you can balance with the rest of the audio tracks. If you prefer to record the sound card's reverb, use WhatUHear as the record source instead of MIDI, but be sure to mute all non-MIDI tracks so they're not included. Another solution is to record each MIDI track as a separate audio track. This gives more flexibility because you can EQ and add reverb to each track separately; however, this requires many separate passes as you solo each MIDI track and record it as described above. The third, and easiest, solution is to select WhatUHear as the record source so you'll capture the exact same mix you hear when you play the song. Then you can record the entire mix either to a new track in your DAW or in another program, such as SoundForge. If you record the entire mix as a new track in your DAW, you'll have to export just that track to a new Wave file, and then delete or mute the track since it's no longer needed. To record the mix in a separate program, simply start that program recording, then switch back to your DAW and press Play.

• Often when you connect an audio device like a mixer to a computer using analog cables a ground loop is created which causes hum. Sometimes you can avoid this by plugging both the mixer and computer into the same physical AC power outlet or power strip. If that doesn't solve the problem, a good solution is to place audio isolation transformers in series with every connection between the two devices. High quality audio transformers can be expensive, but I've had decent results with the EBTECH Hum Eliminator. This device is available in both two- and eight-channel versions, and at less than $30 per channel is reasonably priced for what it is. However, if the highest audio quality is important, and you're willing to pay upwards of $100 per channel, consider better grade transformers such as those made by Jensen Transformers.

Ethan Winer has, at various times, earned a living as a studio musician, computer programmer, audio engineer, composer/arranger, technical writer, and college instructor. He now heads up RealTraps, a manufacturer of bass traps and acoustic treatment.

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