Mixing Multi-Track Audio

Chapter 7

PRACTICAL EXERCISE

Mixing Multi-Track Audio In Chapter 7, we talk about mixing consoles and describe the function of the various controls found on mixing consoles. In this exercise we'll use your favorite digital audio workstation software to mix a multi-track audio recording using the mixing interface. To complete this exercise, you can use any software capable of mixing 56 tracks of audio. We'll show figures demonstrating the process in Logic and Sonar. The purpose of this exercise is to teach you helpful techniques for mixing a multi-track recording, not to teach you how to use your particular software. We'll assume that you're already familiar with your software and have access to help files and resources to learn how to implement the techniques described in this document. With this exercise, you should also have received a folder containing 56 WAV files. These files contain the recordings of various instruments from a recording session with a band called Snowmine. The band has made these raw tracks available through the Shaking Through project, which provides raw track recordings like this for aspiring audio engineers to experiment with. To learn more about the project and to get recordings of other songs, visit: http://www.shakingthrough.com/snowmine With a recording this large, your first goal is to get organized. Begin by loading each audio file into a separate track in your audio software, as shown in Figure 1. Some of these files are pairs of mono files that contain stereo audio from a single source such as a synthesizer. Depending on your audio software, these pairs may get automatically lumped together into a single stereo track. If not you’ll want to make sure to pan those mono track pairs left or right appropriately.

Digital Sound and Music Mixing Multi-Track Audio

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

Figure 1 Each audio file is loaded into a separate track in Logic

With everything loaded into a separate track, you can press the play button and listen to the music. Everything should be there, but because each instrument is on a separate track and not all the tracks were recorded as a single, cohesive performance, some instruments are louder than others. Also, depending on how close the microphone was to the instrument or the location it was recorded, there may be more or less reverberation in the recording. In the mixing process you're trying to adjust the volume of the various tracks and apply appropriate processing to individual instruments, groups of instruments, and sometimes the entire mix to achieve the sound you’re looking for. The next step is to organize the various tracks and sort them by instrumentation. You can listen to each track by pressing the solo button to hear what is on that track. The track or file names may give you some clues as well. You can group the tracks together any way you want, but Table 1 shows you the organization we used. As you identify the tracks, rearrange them so they're adjacent to tracks of similar instrumentation. It also helps to Digital Sound and Music Mixing Multi-Track Audio

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

change the color of the track and the audio region so you can easily identify tracks of each type. Instrumentation Drums Bass

Guitars Keyboards (Keys) Vocals (Vox) Toys

Description Drum tracks including, kick, snare, toms, overheads, and an electronic drum machine Two tracks, one for a direct recording from the direct box and another from a microphone on the bass amp All the various guitar sounds Keyboards, synthesizers, vibraphone, and a prepared (tack) piano. Three vocal tracks. Two on the lead vocal and another for backing vocals Shakers, tambourines, paper lanterns, brooms, etc.

Table 1 Groups and their associated instruments

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

Figure 2 Tracks have been rearranged and color-coded according to their instrumentation

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

With the tracks identified and grouped, the next step is to route the audio signals into mix groups (also called mix busses). Switch to the mixer view of your audio software and create a mix bus channel for each of your groups. Label the bus tracks with the name of the group as well as the color code for that group. The idea here is to route the audio for all the tracks into separate groups for extra control down the road. The result is that you have a bus channel for all the drums, another for all the guitars, and so forth. This way, once you have a good mix of all the instruments in a group, you can adjust the overall volume of that group using the bus fader instead of having to adjust each channel separately, as well as apply additional processing and effects to the overall mix group. Once you have the bus channels created, route the individual audio tracks so that their audio output feeds into the bus for that group. Then route the bus channel's output to the main output for your mix. You may also want to create a bus channel for the entire band mix that is separate from the vocal bus. This way you can adjust the balance between the instruments and the voices using only two faders. Figure 3 shows the mix busses with their routing.

Figure 3 Mix busses for each group

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

One of the most common types of processing you’ll be applying will be reverberation. This is best done at the group level instead of on individual channels. Reverberation plug-ins are very processor-intensive. You can easily use up significant CPU resources running a reverb plug-in on every channel. Also, it typically sounds better if all the instruments in the group are using the same reverb. If not, the various instruments in the group may sound like they're each in a different room. Create some new busses for reverb for the various mix groups. In our case, we created reverb busses for the Drum, Toys, Guitars, Keys, and Vox groups. Insert a reverb plug-in onto each of these busses, and make sure that the reverb mix is set to 100% wet. You’ll be mixing the wet/dry ratio via the bus level faders themselves. Route each reverb bus into the group bus for the intended group. For example, the drum reverb bus should route into the drum bus. This way the reverb bus becomes simply another channel in that group mix. Now create a post-fader aux send on each instrument channel and route it to the appropriate reverb bus. As you work on mixing the various channels, you can add reverb to each channel by increasing the level of the aux send for that channel. Figure 4 shows the reverb buses, along with a few of the Toys instrument channels with their aux sends.

Figure 4 Reverb busses and aux sends for the Toys group

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

Now you’re ready to start mixing. There are many opinions and styles for mixing, and in time you’ll develop your own process. One way is to focus on each group one at a time in the beginning. Start by pressing the Solo button on the drum bus and listen to all the drum tracks together. Adjust the various channel faders to get a balance that sounds good. It may help to pan various channels differently to help them stand out in the mix. You may also want to solo channels individually to hear them alone. For example, you may wish to apply an EQ to the kick drum channel to enhance the low frequencies. You can also start adding reverb to each channel by increasing the aux send level. As you're mixing, watch the level meters on the individual channels as well as on the mix bus channels for clipping. When you mix several signals together, you get an overall level increase so even if the individual channels aren’t clipping, you can still clip the mix bus. The rule of thumb here is to decrease the things you have too much of rather than try to increase the level of the things you can’t hear. This will help you avoid clipping the mix busses. Figure 5 shows an example of how the mix might look for the Drum group channels.

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

Figure 5 Example of the Drum mix

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

Once you have an acceptable mix for each group, you can start to listen to them all together. Now use the mix bus faders to come up with an overall mix. If you need less of the guitars, don’t go back and mess with the individual guitar channels. You already have the guitar mix solved; just reduce the level of the guitar mix bus.

Figure 6 Example bus mix

By now you should have a workable mix. Mixing is never done, however. If you’re doing it right, you’ll never be satisfied with how it sounds. Sometimes a bus or channel level does not work in the mix at a static level. In these cases, you can use automation to change the levels over time. You can also automate panning and processing to change over time throughout the song. Eventually, you have to reach a stopping point and deliver the mix to Digital Sound and Music Mixing Multi-Track Audio

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.

someone to do the mastering. A mastering engineer will take your mix and work with it as a single audio file to apply overall EQ, dynamics processing, and format conversion to optimize the sound for the final listening environment. Included with this tutorial are the demo mix project files for Logic and Sonar, feel free to open them up for examples and ideas, or to simply play with the mix.

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This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743, Jennifer Burg PI, Jason Romney, Co-PI.