Introducing Mixbus And The Ardour3 Alpha

Mixbus (Figure 1) is a version of Ardour2 for Linux and OSX that replaces Ardour's native mixer with one designed by the Harrison company, a manufacturer of professional audio mixing boards. Harrison consoles have been used to mix the soundtracks for many popular movies - see the advertisements on the site - and their products can be found in major broadcast, film, and audio post-production studios, as well as in live performance venues. Mixbus has been designed to emulate the best features of an analog mixer with the added value of Ardour's audio capabilities and Harrison's unique DSP core. Indeed, current Ardour users will find familiar territory in the Mixbus recorder/editor and a whole new world in the mixer section.

Figure 1. Harrison's Mixbus For Linux. (Full-size)

Getting The Goods

I'll get the potential downside out of the way: Mixbus is a closed-source application that sells for real money ($79 US). However, it is also reliant upon to and materially supportive of the Ardour project, and a portion of your Mixbus purchase goes to fund Ardour's development.

Mixbus can be purchased from the Harrison Web site. After retrieving the tarball unpack it in your home directory, enter your new Mixbus-xxx subdirectory, and run the program (as root user). Desktop and menu icons will be installed for easily launching the program, and once the program's installed it's ready for use.

Harrison's recommended minimal hardware requirements for Mixbus for Linux include a dual-core CPU and 1G memory. I tested the program on two machines, a laptop with a dual-core AMD Turion-X2 and a desktop box with a single-core AMD 3800+ clocked at 2.4 GHz. Both machines use nVidia graphics chipsets that are roughly equivalent in performance. Mixbus runs on the 3800, but its screen redraws are struggling to keep up. Audio processing sounds fine on the single-core machine and created no xruns at fairly low latency. However, the sluggish graphics adversely affects the enjoyment and productive use of the Mixbus user interface. By comparison, the laptop's video performance was noticeably better. I can say that Mixbus will run on the 3800, but I will not recommend a single-core box. For best performance heed Harrison's advice and use a multi-core machine.

The Mixer

A multichannel audio mixing board typically includes three primary elements - the channel input strips, the sub-group strips, and the main output controls. Each element may contain various controls, such as level faders, EQ knobs, and solo/mute switches. I/O is usually provided for routing signals to and from external devices to apply effects and other audio processors in pre-fade, post-fade, and sidechain configurations.

The typical software version of an analog mixing console dispenses with fixed controls in favor of a plug-in architecture in which users supply each channel strip with their own favorite EQ, compressor, effects processors, and so forth. Unfortunately, pro-audio industry-standard plug-ins tend to be costly, as is often the case for very high-quality gear. Mixbus reverses the trend by providing its channel strips with their own set of equalizers accompanied by a compressor/limiter (Figure 2), along with a unique tape-saturation stage in the subgroup strips. As you might expect from a company with Harrison's reputation these controls are no mere filler - in fact, they are based on the same technology manufactured for Harrison's hardware consoles, for a mere fraction of the price of one of those beauties. Again in fact, the introductory price for Mixbus is a fraction of the cost of an equivalent suite of pro-audio plug-ins. Incidentally, as per Ardour's original design, Mixbus for Linux accepts LADSPA and LV2 plugins while OSX users can also use plugins in the AU (Audio Unit) format.

Figure 2. The Mixbus channel, subgroup, and master output strips.

Subgroup faders are another common feature on good mixing boards, so naturally Mixbus has subgroup strips, four of them (Figure 2). The output from any channel strip or strips can be routed to any or all of the subgroups for processing a logical group of sources, e.g. the separate components of a drum kit. Each subgroup provides tone controls for further spectral processing and a unique tape saturation control for adding just the right touch of analog warmth to your digital clarity.

The master output strip (Figure 2) is identical to the subgroup strip, with the addition of a K-meter and the use of the Mixbus compressor as the default dynamics processor at the output level fader. The K-meter is a particularly useful feature designed for audio engineers who want the best possible level balances in their master mix. Check out the linked article for more information regarding the K-meter and its significance to contemporary mixers.

The on-screen controls operate smoothly, with no audio glitching or stair-stepping, and when you adjust a Mixbus control you will hear a difference in the sound. You may not be overwhelmed by an effect - unless you're aiming for an overwhelming effect - but you will notice that Mixbus is designed for fine-tuning your audio to whatever degree you desire.

Regarding Control Surfaces

Ardour works nicely with my Behringer BCF2000 control surface, so I tested Mixbus with it too. I put the BCF into its Mackie emulation mode - a configuration that imitates the layout of controllers on a Mackie mixing board - and am happy to report that it works as expected. Unfortunately the combination produced the occasional segfault after moving a fader on the BCF. I have some suspicions about my laptop's USB ports, so I'm not completely convinced that the problem is with Mixbus alone. I also tested the Generic MIDI control surface mode, with the BCF in its default configuration. Performance was considerably better, with no crashes, but I can't claim to have run an exhaustive test.

The Recorder/Editor

The Mixbus recorder/editor window will be familiar to long-time Ardour users, with little obvious change from its source (i.e. Ardour2). However, a look at the track automation view reveals gain control for all of Harrison's additions to the mixer. Automation curves can be assigned to each track's pan, trim, EQ, and compression parameters, giving you the finest control over the audio quality of your mix. In most other respects the Mixbus editor is identical to the editor in Ardour2, so I will refer readers to Ardour's FLOSS manual for more information about its features.

I put the program through a few healthy recording tests, including a number of sessions lasting more than two hours each, with JACK settings of -r48000, -p128, and -n3, stable settings for 8 msecs latency on an Edirol UA25 USB audio interface. All the sessions were recorded in stereo, and I'm pleased to report not a single xrun.


The Mixbus quick-start guide is a 41-page PDF file that provides a basic introduction to the concepts and design of the program. As far as I can tell there's no other printed documentation, but two instructional videos are available for purchase. IMO they are definitely worth their price - $20 (US) per video - and I recommend them especially to new users. Seasoned Ardouristas will get the most from the presentation on mixing, though I must admit that I learned more than a few new tricks about editing in Ardour.

If you're a newcomer to Ardour you'll want to consult the FLOSS manual cited above. Other informative sources include the Ardour forums and the #ardour channel on Freenode IRC. YouTube lists some instructional videos, including an excellent tutorial series by user metalx1000.


Is Mixbus a "game changer" for Linux audio ? In my opinion the answer is a mixed "yes and no". There's no better mixing stage available on any other Linux DAW, and I venture to claim that Mixbus will challenge the mixers in the popular DAWs for Windows and OSX. However, if/when Harrison conjoins Mixbus with Ardour3 then I believe that we'll see greater interest throughout the industry.

Mixbus is also as close as I'm likely to get to owning a Harrison board. It's worth pointing out again that the technology in Mixbus is the same technology that's gone into their high-end mixing desks, with a whopping price difference. Harrison doesn't make a what I'd call a "budget" console - well, not one for my budget - so I'll consider Mixbus their entry-level offering. And it is some offering indeed - Mixbus is available now for a very low introductory price, not at all a bad deal when you note that their next-lowest cost solution runs into thousands of dollars.

Unfortunately there's no demo version available. You can get a pretty good idea of its potential utility by watching Nathan Adam's introductory video on YouTube. A few other Mixbus-related videos are listed there, but I haven't watched them yet.

Ardour3 Public Alpha Test Release

I've cut short this introduction to Mixbus to announce the availability of the first public alpha-test releases from the Ardour3 project. Yes, now you can see for yourself what the wizards at have been concocting in the lab for the last few years. Have no fear, you'll need no full-fledged development environment for these releases - the designers have provided distribution-neutral binaries, so if you've been waiting to check it out now is the time. Yes, bugs are probably present - the purpose of an alpha release is to open the bug-finding stage to a larger community of users, i.e. not just those who know how to set up and employ a Linux applications development environment.

Figure 3. Ardour3's MIDI editor. (Full-size)

Doubtless for many users the biggest new attraction will be Ardour3's MIDI recorder/editor (Figure 3). It is incredibly cool, but just about everything in Ardour3 is cool. I've been won over by its GUI improvements, to the point where I'm a little irritated now by Ardour2's user interface. For instance, the track display in Ardour3 includes a variety of amenities absent in Ardour2, such as multitrack resizing, more logical placement of the resizing tools, the wonderful display manager at the bottom of the track display - I can go on, but it suffices to say that obviously the Ardour3 designers put much thought and labor into finessing the user interface.

This announcement is not intended to be an introduction to Ardour3 - you can get the alpha yourself for that - but I do want to mention Dan MacDonald's tutorial video on Ardour3's MIDI features. Dan's done a nice job for newbies and old hands alike, and he's open to suggestions for improvement. Check out the video and be sure to check out the latest Ardour3 binaries. The Ardour devs want your eyes and ears, so get those bugs reported.


So much development, so little time to report it all. I'll be back in a week or so with more news from the Linux audio world, so check here again soon. In the interim you can check out Mixbus and Ardour3 to keep yourself occupied, and be sure to let us know of any sonic marvels you produce with those wonderful programs. As a matter of fact, I believe I'll head off for another Mixbus session right now. See you next time !

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