Synthesizers can create unique sounds using software input or modify the final sound produced by real instruments, live or sampled. Echo, crunch, delay, and gain are just some examples of the many popular distortion effects that synthesizers make possible.
amSynth (v. 1.2.3)
This simple software synthesizer stands for Analogue Modeling Synthesizer. The AmSynth user interface is modeled after a hardware synth, with knobs dominating the screen. Independently adjustable controls include two oscillators, an oscillator mixer, low pass filter, amplifier, reverb, modulation, distortion crunch, and master volume. Most have several sub-settings. Any combination of settings can be saved as a preset, and amSynth includes 26 presets. This app works well with other audio production applications using JACK. We paired amSynth with Virtual MIDI Piano Keyboard (VMPK) in the ALSA tab of JACK Control, and output directly to system playback.
FreqTweak (v. 0.7.2)
FreqTweak is a realtime audio synthesizer. Processing filters include spectral analysis, EQ cut/boost, pitch scaling, gate, delay, limit, compressor, and warp. Modulators include rotate, rotate LFO, value LFO, and randomize.
The user interface of FreqTweak is pretty efficient. Tabs on top change the function of the upper toolbar. Various fully-editable spectrographs make up the bulk of the window, with output controls located on the bottom. While you might notice that the last news entry on the FreqTweak Web site is from 2004, it has since been updated and the current version is from 2009. The virtual keyboard in ZynAddSubFX works well as a software input for FreqTweak.
Mx44 (v. 1.0)
Mx44 is a real-time software synthesizer that supports up to 16 channels, each with its own settings.
The user interface is a complete mess of poorly labeled sliders. Fortunately, hovering over any of the sliders identifies what it does, as well as provide a text input box with up/down arrows for more precise adjustments. Mx44 works well with Virtual MIDI Keyboard (VMK) through JACK Control.
Qsynth (v. 0.3.5)
Qsynth is a GUI front-end for the command line-only app FluidSynth. Because Qsynth can be controlled entirely from the GUI, it brings all the goodness of FluidSynth to our target audience: new Linux users. Multiple synth engines can be worked on during the same session through the use of tabs, and each engine can hold 16 channels.
Like many software audio production tools, the user interface of Qsynth mimics the corresponding hardware. Knobs and buttons make up the bulk of the Qsynth UI. There is a knob for master, and four knobs each for reverb and chorus. Input boxes with up and down arrows are a nice addition below the knobs for more precise control.
Qsynth comes pre-loaded with about 200 different instruments. This app has no built-in keyboard, so you'll need to connect one via JACK. Virtual MIDI Keyboard works great for this purpose; connect it in the ALSA tab of JACK Control.
terminatorX (v. 3.8.2)
terminatorX is an audio synthesizer and digital DJ application. The DJ aspect allows for 'vinyl scratching' on digital audio files like MP3s. terminatorX can be used live or it can record to a file. Multiple turntables can be created for additional samples. This application also supports LADSPA effects plug-ins.
Turntables are displayed as long vertical strips of knobs, values, and check boxes along the left-hand side of the main window. A green and black waveform for each sample takes up the rest of the application window. For each additional turntable that is added, another waveform appears stacked below the first. And every turntable has an independently adjustable zoom control.
terminatorX is an app that depends on JACK, but the appropriate connections are automatically made to enable playback. After getting a feel for the UI, we were able to create a chipmunk'd version of More Than A Feeling by Boston in no time flat. Unfortunately, terminatorX did crash whenever we attempted to engage the mouse grab feature during playback, rendering the DJing aspect useless for us.
Yoshimi (v. 0.058.1)
Yoshimi is a fork of ZynAddSubFX, and therefore very similar to the original application. Yoshimi is supposed to be easier to connect to JACK than ZynAddSubFX, though we found the ZynAddSubFX connections are automatic, while Yoshimi must be connected manually. ZynAddSubFX also comes with around 300 pre-defined instruments, whereas Yoshimi has none.
The UI of Yoshimi is nearly identical to ZynAddSubFX as far as the control placement, though the forked project is slightly more polished. We like ZynAddSubFX much better for the wider availability, automatic JACK connections, and instrument presets.
ZynAddSubFX (v. 2.4.0)
ZynAddSubFX is a popular software synthesizer application. This app is capable of playing multiple notes and instruments simultaneously. Setting up this application for playback via JACK is about as easy as JACK connections get.
ZynAddSubFX automatically outputs to your system playback inputs. This application also sports a 72-key virtual keyboard and an instrument bank of 300 presets.
The user interface is mismatched, and ZynAddSubFX is a little laggy. Sometimes menu bar items don't respond on the first click, and drop-downs don't appear until the cursor is moved below the selected menu bar item. The main screen, however, is filled with buttons and adjustable selection boxes for various settings, suitably replicating a hardware synth.
Between the relatively hassle-free JACK connections, vast instrument bank, and built-in virtual keyboard, ZynAddSubFX is a go-to application for manipulating sounds, or just quickly playing notes in another application via JACK.