Recently I decided I needed a new guitar amplifier for my studio. Its sole employment would be studio work, so I looked for a small lightweight amp with a good sound, high-quality digital effects, and amplifier/cabinet modeling. Of course I'm always on the look-out for hardware that can be edited from a computer running Linux, and did I mention that a low cost would be nice ? Well, thanks to a timely tip from an on-line friend I discovered that Fender manufactures an amplifier that meets - and exceeds - my expectations. Read on to learn how a Fender Mustang amplifier found a home here at Studio Dave.

The Fender Mustang Amplifiers

I learned about the Mustang thanks to a post from fellow user glokraw on KVRaudio. His enthusiasm was irresistible, so I checked out the amp's specifications on the Fender site and started looking for the best deal.

Figure 1. The Fender Mustang I

As of March 2011 Fender has produced five models of the Mustang amplifer. The versions differ in price, output power, and added features, but they all share the same basic design. I decided to purchase the Mustang I (Figure 1), a 20-watt amplifier with an 8-inch speaker, 24 amp/cabinet presets, 32 built-in effects, aux and headphone jacks, and a class-compliant USB audio output port. For all that goodness Fender suggests a retail list price of $149 (US), but the typical sale price was closer to $99 when I bought mine, a nice bargain for a combined amplifier/effects processor/digital audio interface. However, potential buyers should be advised that the Mustang's USB port is not a general purpose audio connection - it performs best with its originally intended input device, i.e. your electric guitar.

The Inside Report

The overall sound quality is excellent to my ears. Fender claims that the Mustang's speaker is "specially designed", and it does bear up well under heavy distortion and overdrive settings. Clean settings have good presence and definition at high or low volumes, with or without effects. The effects modules are familiar - reverb, delay, flange, chorus, tremolo, distortion, et cetera - and guitarists should find most of their favorite processors here. The amplifier models include some of Fender's famous units, as well as some "British" amplifiers and a couple of less identifiable models. Each amplifier has sets of basic and advanced parameters, among which you'll find twelve cabinet types, also modeled after famous hardware originals.

Figure 2. The Mustang control panel. The USB port is in the lower right corner.

The first sixteen presets can be redefined by the user. Programming a new preset isn't difficult from the amplifier itself - some knobs are dedicated to single parameters while others are multifunctional (see Figure 2) - but the task is made much simpler with editing software. I'll get into the software side after a quick detour to some information likely to be needed by Ubuntu users.

USB Voodoo For Ubuntu

I tested the Mustang's connection to a system running 32-bit Ubuntu 10.04. When I connected the Mustang's USB port to my computer I immediately had a verifiable hook-up between the amplifier and the machine. Running cat /proc/asound/cards revealed that the Mustang was recognized as a full-speed USB audio device known as "FMIC Mustang Amplifier" (Figure 3).

Figure 3. The Mustang/Linux USB connection.

I configured a connections patch in QJackCtl with input from the reported "Mustang Amplifier" and output to my M-Audio Delta 66, but unfortunately that configuration can't achieve low latency without xruns in JACK. In the hope that someone might suggest better settings, here's my command for starting JACK :

  $ /usr/bin/jackd -t5000 -dalsa -r44100 -p512 -n2 -Xseq -D -Chw:4 -Phw:0

where hw:4 is the Mustang and hw:0 is the Delta 66. Despite the relatively high latency - 23.2 msecs - produced by those settings I had no troubles with xruns when recording in Ardour2.

[NB:] See AutoStatic's recommendations in the Comments below. His solution is much better, thanks to the alsa_in utility.

Alas, when I tried to run the PLUG software (see below) I received an error message regarding the USB port. Apparently Ubuntu 10.04 restricts access to USB ports, but the developer quickly posted a simple fix. First I created this file :

  $ sudo gedit /etc/udev/rules.d/50-mustang.rules

which contained the following text : 

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", SYSFS{idVendor}=="1ed8", SYSFS{idProduct}=="0004", GROUP="plugdev"

Then I ran this command :

  $ sudo service udev restart

And now I have no problems connecting PLUG to my Mustang as a normal user.

On The Software Side

After purchasing the amplifier I was eligible for connection to Fender's FUSE Web site. We have a spare desktop machine that runs Microsoft's Vista, so I used that box to establish my account with Fender. The FUSE site provides access to firmware updates, patch collections from other users, and a software editor for the amplifier's settings. The editor is nicely done, but alas, it doesn't work with Linux. It requires a .NET environment and Microsoft's Silverlight, both of which requirements might be met by available Linux tools, but - according to Fender - the native Linux versions are not so feature-complete as their Microsoft counterparts. Those requirements also make it difficult to run the FUSE software under Wine or a virtual Windows session.

I must note here that Fender has shown no hostility towards Linux. In fact, the lead developer of the FUSE software is a Linux user himself, and I had hopes that Fender might develop a Linux version of their editor for the Mustang. However, instead of waiting for that happy day one Linux user began his own software project to access and control the Mustang's many features. Enter the PLUG.

The PLUG Project

PLUG is a simple Qt4-based application (Figure 4) that provides full control of the amplifier and effects stages of the Mustang I and II amps. It's not as flashy as Fender's software, but it weighs about 50 kilos less - no .NET or Silverlight required - and it does what it's designed to do without complications or crashes.

Figure 4. The PLUG Mustang presets editor.

You won't find PLUG in your distribution's repos yet, but the PLUG site offers prepackaged 32-bit and 64-bit binaries that should work on any Linux distribution. If you choose to compile the program from its source code you'll need a development environment that includes the Qt4-dev and libusb-dev packages. When the required components are in place the build process is uncomplicated :

  $ qmake plug.pro
  $ make
  $ sudo make install

As of version 0.5 no icon is installed to launch the program. You can add one of your own - the binary sits at /usr/local/bin/plug - or you can open a terminal and enter plug at the command prompt. When the program starts go to the Connection menu to connect PLUG to the Mustang. If all goes well you'll see the display shown in Figure 4. If the connection fails make sure that the Mustang is turned on and its USB cable is plugged in. Further failure indicates a greater problem that likely needs the attention of PLUG's developer (see below for contact details).

Programming PLUG

PLUG's GUI reveals the Mustang's internal architecture as described above. The main panel is divided into an amplifier editor and an editor for the amplifier's four effects modules. Click the Amplifier or Effect labels to open the settings editors, then adjust the controls with the knobs or by entering values directly into the scrollbox. PLUG's control isn't realtime, but its workflow is fast and efficient - you make your settings, click the Set button to send them to your amp, test the sound and repeat as necessary. Amplifier and effects settings can be retrieved from and loaded to the Mustang together or separately.

If you know nothing about programming a modern guitar amplifier, here are a few tips to get started with PLUG :

• Fender likes hot gain stages. Adjust the various gain controls - yes, there may be multiple gain stages in a preset - to suit your amplitude preference.
• Changing the amplifier and/or cabinet type can make a dramatic difference in the sound. The originals were designed as matched components in specific systems, but you may mismatch at will.
• Load a factory preset. Turn off all effects, then change the amp and cabinet parameter settings one at a time, testing each parameter at various levels. Listen and note the results. Now switch on each effect, one at a time to note how the specific effect changes the sound.
• Make a clean setting without effects as a neutral preset for creating your sounds from scratch.
• Use a neutral patch to test each effect, one by one, then in various combinations. Edit parameters one at a time. Test the effects pre- and post-amp.

Modern amplifiers are typically organized into three main stages. The pre-amp conditions the input signal for further processing, the main amplifier powers the signal, and the effects processor add special characteristics to the input, before or after the main amplifier. For brevity I've oversimplified this design, and of course each stage may have complex internal characteristics.

For my initial project with PLUG I replaced the first sixteen preset slots with my own settings (the Mustang's default gain stages were set too high for my needs). I had already used Fender's nice editor, but I found that I preferred PLUG's easier operation. I quickly filled the presets with my custom sounds, and thanks to the latest PLUG's support for loading and saving preset files I'm now building a handy library of my own sound designs. The PLUG file format is identical to Fender's FUSE preset file format (thanks to Fender's decision to use XML), so I can now share my presets with other Mustang users, regardless of their computer's operating system.

Incidentally, friend glokraw came up with a neat trick. He discovered that he could record from the USB interface and at the same time use the Mustang's headphone output as a second audio source from the amplifier. As he suggested, this configuration makes one "rethink the creative process". His own experiments included driving three patches in the Yoshimi synthesizer with a guitar signal from the Mustang's USB port - MIDIfied via the libaubio tools - while sending the headphone output to a patch in the Rakarrack multi-effects processor. Now that's just crazy cool.

Documentation

User-level documentation consists of a single Web page that describes the basic operation of the program. As usual, you'll learn the most by playing around with it, but if you get stuck you can reach the developer by leaving a message on his site or by checking in on the #linfuse channel at irc.freenode.net. The PLUG site also includes technical information for developers interested in accessing the Mustang's software capabilities.

Looking Forward

On the FUSE user's forum I wrote that a software editor doubles the worth of the hardware. PLUG reconfirms that opinion and has proven its value at Studio Dave. Developer piorekf continues to add useful features to his software. As I completed this review the latest codebase introduced the support for the FUSE file format, and the developer has issued a call for help polishing the GUI. I'd like to see a mechanism to automate firmware updates from Fender (work on this feature has already begun) and it would be cool if PLUG included library functions for collections of presets. Otherwise the program is near feature-complete and definitely stable in its current release.

Outro

A lot of work is going on in the Linux audio world, and I'll do my best to keep up with it. Upcoming articles include profiles of Harrison's Mixbus for Linux, the Open Octave Project's OOM2 sequencer, updated plugins from Loomer, two new native Linux synthesizers, and more. I'm kept pretty busy these days, so stop by again soon to catch up on the latest activities.