Manifold Labs used Linux and real-time patches to build a rack-mount plugin player for audio performers and recordists. Plugzilla runs an embedded 2.4-series kernel, supports eight channels of 24bit/96kHz audio, as well as MIDI, and comes with more than 130 plugins, such as reverb, distortion, drum machines, and more.

Plugzilla, fore and aft
(Click either view to enlarge)
According to Manifold, using computers in recording environments presents challenges, since computers are noisy, can crash, and usually deliver unpredictable levels of determinism, or real-time responsiveness. Additionally, the world of computer audio plugins is divided between proprietary vendors such as Steinberg focusing mainly on VST (Virtual Studio Technology) plugins for Windows and Macintosh, and open source developers writing plugins for LADSPA (Linux audio developers simple plugin API). Plugzilla provides a quiet, robust, real-time Linux system that supports LADSPA plugins, as well as Windows VST plugins through WINE (WINE is not an emulator), the company says.

Plugzilla supports up to eight channels of audio I/O, through gold plated XLR connectors. It currently ships with 130 plugins, and additional supported plugins can be added by users from USB thumb drives, or downloaded directly to the device using software supplied by Manifold labs. Up to eight plugins can run simultaneously, with each filtering up to eight channels, Manifold says.

Audio signals can be routed through plugins using eight knobs and eight switches on the front-panel interface. The knobs can also be used to tune plugin parameters. Routing and parameters can also be controlled by MIDI; the device supports 32 MIDI channels, including four footswitch inputs.

What's under the hood?

Plugzilla is based on an Intel 845 series motherboard with an internal PCI audio card. It includes a 2.0GHz P4 Celeron processor, and 256MB of RAM (expandable to 2GB).

The device boots from a 20GB hard drive, using a 2.6.0 initrd kernel that “decides what application image to boot,” according to Plugzilla developer Don Elwell. “From there, we use the kexec() patches/utility to 'reboot' into the proper application kernel. This allows us to provide updated kernels/applications as a single image, and not have to doodle around with grub configuration files and/or master boot records.

Plugzilla's primary kernel is currently based on Linux 2.4.22, with a number of real-time patches. “We started out doing our own patched kernel, but discovered the Con Kolivas patches [link], and use those now, plus a few extras for good measure,” Elwell said.

Elwell adds that Manifold is currently evaluating a preliminary port of its applications and drivers to a 2.6-series Linux kernel. Improved real-time performance is among the features touted in Linux 2.6.

The kernel boots Plugzilla into a Linux port that Manifold Labs developed in-house, based on Red Hat 8.0. In addition to WINE, which enables Windows DLLs such as VST plugins to run under Linux, Plugzilla leverages a number of open source software packages. For example, rsync is used for local and network updates, according to Elwell. The device does not use Linux audio or USB drivers, however.

“When we started this project, ALSA was pretty slow and incomplete, and Jack didn't exist, so we wrote our own PCI bus matering audio device drivers,” Elwell said. (ALSA is a project to develop an advanced audio and MIDI framework for Linux; Jack is a free low-latency audio connection and routing kit for Linux and MacOS.)

Manifold also wrote Linux drivers for several pieces of custom hardware included in the device, such as the front panel user interface and rear panel I/O. “The front and rear panel controls are USB devices. These use a custom protocol — USB HID was just too complicated for what we needed,” notes Elwell.

According to Elwell, the biggest challenges Manifold faced in creating Plugzilla were understanding the undocumented nuances of VST plugins, getting real-time low-latency performance out of the Linux kernel, and developing Linux device drivers. Another challenge was achieving good low-latency performance via USB, which was required for MIDI.

Availability

Plugzilla is available now, priced at about $3,000. Two expansion options are also available. One adds four additional XLR I/O ports,while the other adds AES/EBU, word clock I/O, 10/100 Ethernet, USB 1.1, and USB-B.

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