Why Use Mix Bus Compression?
Mix bus compression can be a mysterious and confusing topic for novice mixers. Many top engineers swear by it, claiming that it can add depth, punch, and glue to a mix. However, it can seem like a dark art if you are new to mixing. So, why use mix bus compression?
Compressing the mix bus can do many things for your music. Yes, it can add punch and glue. It can help the music to breath and move as a whole. It can help to bring out subtle elements in the mix, creating greater sonic depth. It can also help to smooth out transient peaks and raise the RMS levels. Most importantly, it can help to add emotion and impact to a mix.
In the analog days, mixers were able to push levels into the red without the fear of harsh digital clipping. This caused the console to saturate and compress the signal, creating a pleasing sonic timbre. Mixing in the box, we do not have the benefits of analog circuitry and cannot push signal into the red. However, using a mix bus compressor can have a similar effect.
Setting the threshold creates a "ceiling" for your mix. Pushing level into this will cause the compressor to react. The sound of your mix will change depending on how much compression is used. This can help to "squeeze" the mix during the loudest sections and open up during quiet parts. Using mix bus compression you will be able to craft more "analog" sounding mixes. However, improper use of this can ruin the sonics. Too much compression can cause things to become dull and lifeless. In fact, an over compressed mix bus can completely destroy the groove and impact of the music. Here are some tips to help when using mix bus compression.
When using mix bus compression, it is always important to listen critically. Engineers need a way to be sure that they are making accurate mix decisions. Sometimes things can sound great in the studio but, horrible when played on other systems. To listen in the most accurate way possible, use Soundways' Reveal plug-in.
Reveal was created to help engineers ensure that their mixes will translate accurately to other systems. It works by allowing engineers to focus on the audio core. The core is the frequency range to which the human ear is most sensitive, 2kHz - 5kHz. First, place Reveal on your master bus. Then, engage Critical Listening mode when making important mix decisions. Listening in this context, you can be sure that you are making precise adjustments which will translate accurately to all speaker systems.
Tip #1: Choose a Compressor
It is important to choose the appropriate type of mix bus compressor for the music. Different compressor types will yeild different sonic results. Some may work better for certain genre's than others. Be sure to choose the right compressor for your mix.
VCA compressors are known for adding punch to a mix. The famous SSL G-series, API 2500, and Neve 33609 use this solid-state design. VCA's are known for gluing the mid-range and causing the music breath. These are a great choice for more aggressive styles of music like rock, hip-hop, and edm.
Variable mu style compressors are another common choice for the mix bus. This design uses a tube to acheive the compression, creating subtle harmonic distortion. Famous models like the Fairchild 670 and Manley Vari-Mu yeild a warm, smooth sound. Vari-mu's are an excellent choice for acoustic styles of music like folk, blues, or even jazz.
Optical compressors are very popular for mixing. However, they are sometimes thought to react too slowly to be used on the mix bus. In recent years, this has changed with the introduction of models like the Pendulum OCL-2, Tube-Tech CL2A, and Avalon AD2044. These produce a very clean, transparent sonic character.
FET compressors are another popular design. Due to the fast nature of the circuit, FET compressors are often thought to be used for peak limiting. However, there are a few models like the Daking FET 3 and Universal Audio 1176 that work well on the mix bus.
Be sure to consider these options when choosing the right compressor style for your mix.
Tip #2: Adjust the Settings
Once you have chosen your compressor, it is now time to adjust the settings. Compressors will have different parameters depending on the type. However, they all work in a similar manner. When adjusting the settings, be sure the use Reveal's Critical Listen mode. This will ensure that you are listening in an accurate manner, and make precise adjustments.
I like to start with the threshold or input. First, I like to make sure that my kick drum is set to the appropriate level. Then, I will lower the threshold until I start to see gain reduction. The mix bus compressor should be reacting very slightly to the kick drum hits, usually -0.2dB - 0.5dB. I must stress that the needle should barely be moving. Properly setting the threshold will create a "ceiling." Pushing level into this will cause the compressor to react, reducing dynamics and creating a more aggressive sound. Once you have set the threshold, now adjust attack and release times.
It is best to use long attack times when compressing the mix bus. This will allow transients to come through, while reducing the overall dynamics. The release time should be set to the groove and tempo of the music. If you are new to mixing, using automatic release times is highly recommended. Setting a release time that is too fast can cause unpleasant pumping. A release time that is too slow can kill dynamics and cause a mix to become dull. Adjust the release so that the compressor returns to 0dB gain reduction on the downbeats. Be sure to listen with a musical ear when setting the release time.
Tip #3: Push Faders
Once you have adjusted the settings of your compressor, now it is time to move some faders. Start pushing level into the compressor and listen carefully. As the compressor reacts, the sonic results will change. Listen to how things change as the level increases and decreases. Listen for how pushing some elements of your mix may affect others.
Be sure to listen for when you've hit the "sweet spot." This is the point at which the the mix starts to take shape and become lively. You may not hear when you've hit the sweet spot but, likely you will feel the result.
Tip #4: Listen For Groove and Emotion
You should always listen for groove and emotional impact when mixing. This is especially important when using mix bus compression. The compressor can potentially over-react, changing the groove and reducing impact. Be sure to lisen for this throughout the mixing process. If you find that you are losing emotional impact or the groove has changed, check the compressor. You may find that the compressor is causing a lot of gain reduction. If this is the case, try adjusting the threshold until the appropriate level is achieved.
Tip #5: Don't Over-do It
It is important to remember that too much compression on the mix bus can completely kill sonics. Check the mix bus compressor frequently to be sure that there isn't too much gain reduction. More than -1dB of gain reduction will likely change the mix. At times this can be needed however, it can often cause the transients to be drastically reduced. Be sure not to over-do mix bus compression but, if it sounds good stick with it. Using these tips you will be able to apply mix bus compression with a high level of precision and subtlety.