PreSonus Blog

The “Double-Decker” Pre-Main Bus

This Friday tip has multiple applications—consider the following scenarios.

You like to mix with mastering processors in the Main bus to approximate the eventual mastered sound, but ultimately, you want to add (or update) an unprocessed file for serious mastering in the Project page. However, reality checks are tough. When you disable the master bus processors so you can hear the unprocessed sound you’ll be exporting, the level will usually change. So then you have to re-balance the levels, but you might not get them quite to where they were. And unfortunately, one of the biggest enemies of consistent mixing and mastering is varying monitoring levels. (Shameless plug alert: my book How to Create Compelling Mixes in Studio One, which is also available in Spanish, tells how to obtain consistent levels when mixing.)

Or, suppose you want to use the Tricomp or a similar “maximizing” program in the master bus. Although these can make a mix “pop,” there may be an unfair advantage if they make the music louder—after all, our brains tend to think that “louder is better.” The only way to get a realistic idea of how much difference the processor really makes is if you balance the processed and unprocessed levels so they’re the same.

Or, maybe you use the cool Sonarworks program to flatten your headphone or speaker’s response, so you can do more translatable mixes. But Sonarworks should be enabled only when monitoring; you don’t want to export a file with a correction curve applied. Bypassing the Sonarworks plug-in when updating the Project page, or exporting a master file, is essential. But in the heat of the creative moment, you might forget to do that, and then need to re-export.


The Pre-Main bus essentially doubles up the Main bus, to create an alternate destination for all your channels. The Pre-Main bus, whose output feeds the Main bus, serves as a “sandbox” for the Main bus. You can insert whatever processors you want into the Pre-Main bus for monitoring, without affecting what’s ultimately exported from the Main bus.

Here’s how it works.


  1. Create a bus, and call it the Pre-Main bus.
  2. In the Pre-Main bus’s output field just above the pan slider, assign the bus output to the Main bus. If you don’t see the output field, raise the channel’s height until the output field appears.
  3. Insert the Level Meter plug-in in the Main bus. We’ll use this for LUFS level comparisons (check out the blog post Easy Level Matching, or the section on LUFS in my mixing book, as to why this matters).

Figure 1: The Pre-Main bus, outlined in white, has the Tricomp and Sonarworks plug-ins inserted. Note that all the channels have their outputs assigned to the Pre-Main bus.

  1. Insert the mastering processors in the Pre-Main bus that you want to use while monitoring. Fig. 1 shows the Pre-Main bus with the Tricomp and Sonarworks plug-ins inserted.
  2. Select all your channels. An easy way to do this is to click on the first channel in the Channel List, then shift+click on the last channel in the list. Or, click on the channel to the immediate left of the Main channel, and then shift+click on the first mixer channel.

With all channels selected, changing the output field for one channel changes the output field for all channels. Assign the outputs to the Main bus, play some music, and look at the Level Meter to check the LUFS reading.

Now assign the channel outputs to the Pre-Main bus. Again, observe the Level Meter in the Master bus. Adjust the Pre-Main bus’s level for the best level match when switching the output fields between the Main and Pre-Main bus. By matching the levels, you can be sure you’re listening to a fair comparison of the processed audio (the Pre-Main bus) and the unprocessed audio that will be exported from the Main bus.

The only caution is that when all your channels are selected, if you change a channel’s fader, the faders for all the channels will change. Sometimes, this is a good thing—if you experience “fader level creep” while mixing, instead of lowering the master fader, you can lower the channel levels. But you also need to be careful not to reflexively adjust a channel’s level, and end up adjusting all of them by mistake. Remember to click on the channel whose fader you want to adjust, before doing any editing.

Doubling up the Main bus can be really convenient when mixing—check it out when you want to audition processors in the master bus, but also, be able to do a quick reality check with the unprocessed sound to find out the difference any processors really make to the overall output.

Acknowledgement: Thanks to Steve Cook, who devised a similar technique to accommodate using Sonarworks in Cakewalk, for providing the inspiration for this post.

  • I was talking about the DAW, I can’t give you any advice about the plugin, sorry.

  • Trevis Williams

    Harrison Mixbus 32C plugin is it worth the upgrade. I have the cheap demo one.

  • Ahmed Salah

    hmmm old scenarios, the best part of it is “The only way to get a realistic idea of how much difference the processor really makes is if you balance the processed and unprocessed levels so they’re the same.”

  • Q K

    I wish this can be a built in feature in Studio One. Or at least have an option in the preferences.

  • I miss this feature. I used to have it when I mixed in Harrison Mixbus 32c.

  • Tifosi Fratello

    Yeah, like a sticky. Even being able to detach and throw it on another screen would be nice.

  • Wilton James

    this work-around is kool but Studio One needs a control room section (similar to cubas/nuendo) where the monitoring plugins (metering/Room correction/etc) can reside outside of the project/song so these plugins dont change from mix to mix.

  • Ah, thanks. That makes a lot of sense. It’s the comments that make these tips more valuable to readers.

  • Barry Banaanuitstraling

    Oh, I’m still mixing into the extra bus like you. It’s just SW that’s on the Mains instead of the ‘MIx Bus’ (Pre-Main) in your setup. I never forgot to turn it off since I work this way.

  • Yes, that works too, and has the advantage of not requiring the extra bus. But, I find using the extra bus more convenient to switch back and forth between the dry sound and the one with effects in the Main bus. If I make a change In the Main bus effects, then I need to open an effect UI, and toggle back and forth between having the Main bus inserts on and off, while adjusting the effect’s level. I found it easier to adjust the fader on the second bus to compensate for any changes.

    Another advantage I didn’t mention in the original text is that I like to mix at low volumes, but occasionally switch over to a louder one as a “reality test.” So in addition to using the doubled main bus to match levels, it’s also easy to set it to different levels while mixing, and switch to the Main bus when you need a reference. You can do the same thing by inserting a Mixtool in the master bus, and switching it in and out as needed. But since I already have the doubled bus set up for other purposes, I just use that instead. One of the things I really like about Studio One is that there are often several ways to do the same thing, so you can choose the option that fits your workflow best.

  • Gavin Steiner

    I wish we could create a bus like this and have it stay in view when scrolling horizontally like the Main bus does. This was so valuable in Sonar.

  • Nick Osher

    Interesting insights. i also use this technique in a similar fashion on every mix. I think the main reason being that i hate latency in every way and I try to keep my Stereo Bus as dry as possible. For that reason i started using a “Pre Stereo bus Bus” to act like a buffer in a certain way, as you said. Honestly it makes me feel safer with a mix or maybe even a feeling of a Gods Eye View of the entire mix. Maybe I’m just OCD. But good tips . Thanks Craigers

  • Barry Banaanuitstraling

    I work the same way, but add SW to the Mains bus and bypass Master FX on exports and Update Mastering File. That way you’ll never forget to turn it off (and Mix FX like Console Shaper or Softube Tape are still included). It’s just a pity that the Song Setup option ‘Include effects when updating mastering file’ is not being set in a template, so you always have to think of turning it of for each new song.