Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time
                    A software synthesizer plugin for the
                          DSSI Soft Synth Interface

Xsynth-DSSI is a classic-analog (VCOs-VCF-VCA) style software
synthesizer which operates as a plugin for the DSSI Soft Synth
Interface.  DSSI is a plugin API for software instruments (soft
synths) with user interfaces, permitting them to be hosted
in-process by audio applications.  More information on DSSI can be
found at:

Xsynth-DSSI is written by Sean Bolton, and copyright (c) 2010 under
the GNU General Public License, version 2 or later.  See the enclosed
file COPYING for details.  While this software is 'free' within the
requirements of this license, I (Sean) would appreciate any or all
of the following should you find Xsynth-DSSI useful:

    - an email stating where you're from and how you're using
        Xsynth-DSSI, sent to <musound /at/ jps /dot/ net>.
    - copies of or links to music you've created with Xsynth-DSSI.
    - any patches you create for Xsynth-DSSI.
    - suggestions for improving Xsynth-DSSI.
    - offers of paying work writing this sort of code!

Xsynth-DSSI is based on Steve Brooke's Xsynth 1.0.2, which is
available (also under GPL) at:

Xsynth-DSSI retains the basic synthesis model of Xsynth, while
adding the following features:
    - operation as a DSSI plugin,
    - polyphonic operation,
    - band-limited oscillators,
    - a new, more stable filter mode, and
    - velocity-sensitive envelopes.

Xsynth-DSSI requires the following:

    - DSSI version 0.9 or greater, available from the address above.

    - liblo version 0.12 or later (0.23 or later recommended), a
        library implementing the Open Sound Control (OSC) protocol,
        available at:

    - pkgconfig with PKG_CONFIG_PATH set appropriately to pick up
        DSSI and liblo.

    - GTK+ version 1.2 or 2.x.  (If GTK+ is not found, the plugin
        will be built without the GUI.)

    - the LADSPA v1.x SDK.

    - the ALSA headers (DSSI plugins use ALSA structures, but not
        the actual drivers, so you don't necessarily need the
        drivers installed.)  Users of non-Linux systems can use
        libdssialsacompat, available at:

    - a working DSSI host.  Xsynth-DSSI has been tested with
        jack-dssi-host, available in the DSSI distribution, and with
        ghostess, available at:

    - automake 1.7, autoconf 2.58, and libtool 1.4.3 or better if
        you wish to recreate the build files.

The generic installation instructions in the enclosed file INSTALL
aren't particularly helpful, so try this instead:

1. Unpack the tar file.

2. Make sure PKG_CONFIG_PATH is set correctly to locate the
    dssi.pc and liblo.pc pkgconfig files.  On many systems, this
    will be:

    $ PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
    $ export PKG_CONFIG_PATH

3. 'cd' into the package directory and execute './configure'.
    configure will add '-Wall' and my favorite optimizations to
    CFLAGS for you if you don't include any '-Wall' or '-O' options.
    If you're using gcc and wish to provide your own optimization
    flags, you MUST at least use '-finline' and a non-zero '-O' flag
    to get decent results.

4. Enable debugging information if you desire: edit the file
    src/xsynth.h, and define XSYNTH_DEBUG as explained in the
5. Do 'make'.  Hopefully it should build without warnings (or

6. 'make install' will install the following:


Feedback on your experiences building Xsynth-DSSI is appreciated.

To run the Xsynth-DSSI plugin under the jack-dssi-host provided in
the DSSI distribution, I do the following:

1. Start JACK.

2. Start jack-dssi-host, supplying the correct plugin path
    and filename (substitute <prefix> as appropriate):

    $ DSSI_PATH=<prefix>/lib/dssi sudo jack-dssi-host

    jack-dssi-host should start, and moments later the Xsynth-DSSI
    graphic user interface should appear.

3. Use aconnect or kaconnect to connect jack-dssi-host to a MIDI
   source, such as vkeybd.

4. Begin playing sounds!  If you get no response, try clicking the
    'Send Test Note' button in the Xsynth-DSSI GUI. This sends a
    note directly via the host to the plugin, so if you hear sound
    now, look for a problem between the example host and your MIDI
    source.  If you still don't hear sound, I'd look for a problem
    between the example host and your output device.  If you
    continue having trouble, you might recompile with XSYNTH_DEBUG
    bit 2 set, which will cause the plugin to continuously output a
    quiet buzz to help debug your outgoing signal path.

Xsynth-DSSI starts up with a small set of sound presets, or
'patches', that you can select either by selecting the GUI 'Patches'
tab and clicking on the patch name, or by sending a MIDI program
change from your MIDI source with the appropriate program number.

File Menu
You may load additional patches by selecting 'Load Patch Bank...'
from the GUI 'File' menu, and pointing the file selection dialog to
a Xsynth-DSSI patch bank file.  One such file is patch_library.Xsynth,
which is installed with the plugin, in <prefix>/share/xsynth-dssi/.
After selecting a patch bank file, you will be asked at which
program number to begin loading the new patches.  This allows you to
overwrite the existing patches, or to add the new patches at the
end.  Note that if the starting program number you select, plus the
number of patches in the patch file, exceeds 128, the additional
patches will not be loaded.

Selecting 'Save Patch Bank...' from the 'File' menu will allow you
to save your patch bank to a file.  After specifying the file name,
you will be asked to specify the range of patches to be saved.

Patches Tab
Selecting the 'Patches' tab displays a list of all the patches loaded.
Clicking on the name of a patch causes that patch to be selected.

Test Note
The 'Test Note' controls allow you to send a test note to the
plugin, by clicking on the 'Send Test Note' button.  Changing the
'key' and 'velocity' sliders will change the pitch and velocity of
the test note.  A key of 60 is generally considered to be
'Middle C'.

Patch Edit Tab
This tab allows you to edit patches.

The controls in the VCO1, VCO2, LFO, MIXER, PORTAMENTO, EG1, EG2,
VCF, and VOLUME sections all offer real-time control of the
synthesis parameters used by the plugin to create sound.  The voice
architecture is described in more detail below.

Note that the rotary knobs may be manipulated in several ways:
    - Clicking and dragging a knob with mouse button 1 sets the
        value directly, by making the knob pointer point toward the
        mouse pointer.
    - Clicking and dragging a knob with mouse button 3 allows
        incremental adjustment of the knob's current value (without
        a sudden jump.) Horizontal movement produces large variation
        in the knob value, while vertical movement allows finer
    - Clicking on a knob with buttons 1 and 3 increment and
        decrement the knob value.

The NAME text box allows you to change the name of a patch.

Once you have edited a patch to your satisfaction, you may save it
back to the patch bank by clicking the 'Save Changes' button.  You
will be asked to which program number you would like to save your
new patch.  If you do not wish to overwrite an existing patch,
selected the highest available patch number, next to which '(empty)'
will be displayed, to save your changes to a new slot.  Be sure to
then use 'Save Patch Bank...' from the 'File' menu to save your
changes to a file.

Configuration Tab
Tuning: Sets the tuning of this instance of the plugin, as Hz for

Polyphony: Sets the maximum polyphony for this instance of the
    plugin.  If you attempt to play more notes than this setting,
    already-playing notes will be killed so that newer notes can be
    played.  If you are getting xruns, try reducing this setting.

Monophonic Mode:
    'Off'  - polyphonic operation.
    'On'   - monophonic operation, where the envelopes are
             retriggered upon each incoming note on event. 
    'Once' - monophonic operation, where the envelopes are triggered
             only on the first note on of a legato phrase -- that
             is, if you hold one note while playing a second, the
             envelopes will not be retriggered for the second note. 
    'Both' - monophonic operation, where the envelopes are
             retriggered at each note on, and upon note off when
             other keys are still held.

Glide Mode:
    'Legato Only' - portamento (a 'slide' in pitch between two
             notes) is only used when a new note is played while
             another is held.
    'Non-legato Only' - portamento is only used for single
             (staccato) notes, or the first note of a legato phrase.
    'Always' - portamento is always used.
    'Leftover' - like 'Always', but ... more difficult to predict.
    'Off'  - disables portamento.

Pitch Bend Range: Set the pitch bend range, from 0 to 12 semitones,
    for this instance of the plugin.

Voice Architecture
Xsynth-DSSI models a simple analog synthesizer, where two
oscillators (VCO1 and VCO2) are mixed (MIXER) and fed to a low pass
filter (VCF), which then feeds an amplifier (VCA) controlling the
output volume:

    MIXER --> VCF --> VCA --> output

Modulation of these elements is possible using two envelope
generators (EG1 and EG2), a low-frequency oscillator (LFO), and the
MIDI key and velocity.

Oscillators VCO1 and VCO2
The frequencies of VCO1 and VCO2 are controlled by the MIDI key,
plus the value of the 'pitch' control.  Compared to a base pitch of
'0', a value of '5' is one octave higher, and a value of '10' is two
octaves higher.

The pitch from the MIDI key may be lagged by the PORTAMENTO 'glide'
value, as determined by the glide mode and other keys in play (see

The frequency of VCO2 is also affected by the 'pitch mod' amounts
from EG1, EG2 and the LFO.

The waveforms available for both oscillators are:
    0. sine
    1. triangle
    2. ascending sawtooth
    3. descending sawtooth
    4. square
    5. variable-width rectangle
    6. variable-slope triangle

The 'pw/slope' control sets the width and slope of waveforms 5 and
6, respectively.  It has no effect when waveforms 0 through 4 are

VCO2 may be 'hard synced' the VCO1, so that its phase resets
whenever VCO1 completes a cycle, by selecting the 'osc sync'

A 'balance' setting of '0' causes the mixer to output only VCO1, a
setting of '10' outputs only VCO2, and a setting of '5' results in
an equal mix of both.

Low Pass Filter VCF
The VCF cutoff frequency is set by the 'cutoff' control, plus the
'filer mod' amounts from EG1, EG2, and LFO.

The filter resonance, or 'Q', is set by the 'resonance' control.  Be
aware that the filter is not always stable when the resonance is
very high, and when the resonance is very low but the cutoff is very

The 'mode' option menu controls which of the three filters is used:
    '12 db/oct' - the original Xsynth two-pole filter.
    '24 db/oct' - the original Xsynth four-pole filter.
    'MCVLPF-3'  - Fons Adriaensen's MCVLPF-3, modeled after the
                  voltage-controlled lowpass filter invented by
                  R. A. Moog.

Amplifier VCA
The gain of the VCA set by both the 'volume' control and the
envelope generator EG1.

Envelope Generators EG1 and EG2
The envelope generators are classic 'ADSR'-style: the 'attack'
control sets the time it takes from key-on for the envelope to reach
full output, the 'decay' control sets the time it then takes to fall
to the 'sustain' level, where it stays until key-off.  The 'release'
control sets the time it then takes to fall back to zero output.

The 'vels sens' (velocity sensitivity) control determines the amount
the envelope output is reduced by low MIDI velocities.  At a
sensitivity of '0', the envelope always goes to full output.  At
maximum MIDI velocity (127), the envelope always goes to full
output.  Otherwise, the lower the velocity and higher the
sensitivity, the greater the reduction of the envelope's output.

Low-frequency Oscillator LFO
The duty cycle of the waveform 5 (rectangular) is fixed at 25% high,
and waveform 6 (variable-slope triangular) is not available.

MIDI Controller Mapping
For DSSI hosts that support MIDI controller mapping, Xsynth-DSSI
requests that they map two MIDI controllers:

- MIDI Control Change 5 "Portamento time" is mapped to the
    PORTAMENTO 'glide' control, although in a somewhat backward way:
    higher CC values map to shorter glide times, and lower CC values
    to longer glide times.

- MIDI Control Change 8 "Balance" is mapped to the MIXER balance

Xsynth-DSSI itself interprets several other MIDI control messages:

- MIDI Control Change 7 "Volume" controls the output level, without
    affecting the VOLUME control.

- MIDI Control Change 1 "Modulation wheel" reduces the VCF cutoff.

- MIDI channel pressure and key pressure are combined to boost the
    VCF resonance.

Questions that might be frequently asked
Q. Woah! Where'd that nasty sound come from?
A. A certain grittiness has always been part of Xsynth's charm for
    me, but if you're getting really nasty sound from a patch, check
    for the following:
    - Volume too high: especially when using high resonance, your
        signal may be so hot it's clipping.
    - Resonance too high: yep, the filter will go to
        self-oscillation with high resonance settings. Try backing
        the resonance off.
    - Resonance too low: Xsynth's filter is unstable near zero
        resonance when used with high cutoffs.  Try setting the
        resonance to 0.2.
    - Resonance getting boosted by keyboard or channel pressure: try
        playing softly or turning your keyboard's pressure
        sensitivity off.  I know, this should be configurable....
    - XSYNTH_DEBUG XDB_AUDIO set: if you've got a ~600Hz buzz in the
        output even when you're not playing anything, your plugin
        was probably compiled with the XDB_AUDIO debug bit set.  Fix
        that and recompile.
    - Pitch too high: even with the band-limited oscillators, it is
        possible to get audible aliasing on very high notes.  This
        is especially true when using oscillator sync while VCO2 is
        producing a sine wave, since the band-limiting technique
        doesn't deal as well with waveforms having continuously
        varying slope.

Q. Help! I just installed Xsynth-DSSI 0.9.x, and now my sessions
    that used the older Xsynth-DSSI 0.1.x don't sound right.  What
    should I do?
A. Xsynth-DSSI 0.1.3 is the last 0.1.x-compatible version, but it
    does include the anti-aliased oscillators and MVCLPF-3 filter.
    If you just want to use your existing sessions, you'll have to
    use version 0.1.3. If you want to convert them to 0.9.x, you'll
    need to save any custom patches or patch banks using a 0.1.x
    version, then install 0.9.x, load the custom patches, then tweak
    the mix and glide settings as needed.  (Note that the version
    0.1.x default patch set is installed by later versions as

Q. Why aren't the GUI slider values and the corresponding LADSPA
    port values the same?
A. The LADSPA port values are the actual numeric values used by the
    synthesis code, while the GUI slider values are all the 0-to-10
    values used in Steve Brookes' original Xsynth interface.


A classic-analog (VCOs-VCF-VCA) style software synthesizer DSSI plugin







No releases published


No packages published