MSS (Modular Soft Synth)

• Change Log
• Overview
• The MSS GUI
• System requirements
• MIDI input limitations
• Installation
• Configuration
• Basic principles
• Using the synth
• Getting started
• Real time aspects
• Module parameter settings & intermodule dependencies
• Module configuration examples
• Module reference
• WTOscillator
• WaveTable
• PlainOscillator
• WaveGuideOscillator
• AGOscillator
• Filter
• SimFilter
• MFilter
• BiquadFilter
• AllPassFilter
• MultiDelay
• LFOscillator
• Adsr
• PinkNoise
• Comments & questions
• Debugging & bug reporting
• Links

Change Log

Overview

MSS is a modular synthesizer, i.e the synthesizer module configuration (in terms of the number and type of synthesizer modules, and how they are interconnected) is not fixed. MSS includes a set of synthesizer module types like different kinds of oscillators, filters, envelope generators and so forth (the available module types are described in  Module reference ). The synthesizer configuration can in principle be any set of module instances selected from the available module types. New module instances may be added and interconnected via menu choices. It is possible to setup very complex configurations in this way. The limiting factor is in practise probably the available computer resources (CPU speed), and maybe your own imagination in creating complex configurations.

MSS is just a synthesizer. It does not provide any sequencing or recording functionality at all, i.e you can only play it yourself and you can't save your performance. It is simply just an instrument.

The module configuration (including the parameter settings in each module) can be loaded from or written to file. MSS includes a small set of example module configurations, see Module configuration examples.

The MSS GUI

The GUI is distributed on two windows, a nice keyboard window and a not-so-nice control window. The keyboard window is very much inspired from the Ultramaster Juno-6 keyboard (see http://www.ultramaster.com/juno6/index.html). Any credit for the keyboard design goes to Ultramaster. The control window can be blamed on me. The control window contains all the synthesizer modules. It simply groups all synthesizer modules according to module type, i.e oscillators together, ADSR envelope generators together etc. All synthesizer modules have simple sliders/radio buttons to control the synthesizer module parameters.

The most annoying aspect of the control window GUI is probably that the connectivity among different modules is not directly visible in the GUI. You have to open the pop-up menu on a particular module to see what other modules are connected to its inputs. This makes it possible to get a grasp of the module interconnectivity, but it is far from user friendly.

System requirements

Hardware requirements

An example: On my Pentium II 450 MHz around 28 % of the CPU is needed to play 4 simultaneous notes (using 2 oscillators, 2 filters, 4 envelope generators and 1 LFO). The load on the CPU increases if I play more notes or if I increase the number of modules in the configuration.

So there is no precise recommendation on how fast a CPU is needed to play this synth. The faster the better is the general recommendation, since you can then use more modules (giving more possibilities to create interesting sounds) in the configuration without running out of CPU cycles.

Software requirements

Software requirements is basically Linux plus GTK+ version 1.2 (available via http://www.gtk.org/). If you want to build MSS from the sources you need GTK+, libpthread and libgthread. If you download the statically linked executable you don't need to have any of these installed. MSS is implemented in C++, so you'll need g++ to build it from the sources.

MSS has been developed and tested only on Red Hat Linux 7.0 running on a Pentium II with GTK+ version 1.2 and an ESS Maestro-2 based soundcard. MIDI input from an external keybord has been tested only with a Technics KN501 MIDI keyboard connected via the serial port. In principle, MSS should compile and run without problems on any x86 Linux with an adequate OSS driver.

MIDI input limitations

Installation

1. unpack mss-<version>-src.tar.gz. The command 'tar zxpf mss-<version>-src.tar.gz' will create the mss<version> directory containing the MSS source distribution in your current directory.
2. cd into the mss<version> directory.
3. configure the synth as needed according to chapter Configuration.
4. build the synth from sources (command 'make')
5. install the synth (command 'make install'). If possible, you should install MSS as root (see  Real time aspects)
6. run the synth by issuing the command './runsynth.sh' in the installation directory.

1. unpack mss-<version>-bin.tar.gz. The command 'tar zxpf mss-<version>-bin.tar.gz' will create the mss<version> directory containing the MSS binary distribution in your current directory.
2. cd into the mss<version> directory.
3. configure the synth as needed according to chapter Configuration.
4. generate the wave tables (command 'make -C tools tables'). This step is not absolutely necessary, but it will reduce MSS startup time.
5. install the synth (command 'make install'). If possible, you should install MSS as root (see  Real time aspects)
6. run the synth by issuing the command './runsynth.sh' in the installation directory.

Configuration

• Edit INSTALLDIR in the top level Makefile, i.e choose in which directory to install MSS.
• Edit the synthconfig file.
• Edit the synthrc file. It is a standard GTK resource file where some graphical aspects can be configured (not really needed)

• midiDevice is the device from which MIDI input from an external keyboard is read. This is typically one of the serial ports or /dev/midi.
• dspOutput_sampleRate is the sample rate (in Hz).
• dspOutput_controlRate is the control rate (in Hz).
• dspOutput_channels is the number of channels. Supported values are 1 (mono) or 2 (stereo).
• dspOutput_bits is the number of bits per output sample. Supported values are 8, 16 and 24 bits.
• dspOutput_numFrags and dspOutput_fragSize define the amount of buffering done in the sound card before output to the DSP D/A converter.
• dspOutput_deviceName is the device to which samples are written for output. This should be a DSP device on your sound card.

These are the default settings in the synthconfig file:

midiDevice            /dev/ttyS0
dspOutput_sampleRate  44100
dspOutput_controlRate 1000
dspOutput_channels    2
dspOutput_bits        16
dspOutput_numFrags    3
dspOutput_fragSize    1024
dspOutput_deviceName  /dev/dsp

If you change the sample rate to anything else than the default 44100 Hz, you should be aware of an optimization done in MSS in order to reduce startup time: At startup MSS tries to open two big wave table files (parabolaTable and sawTable in the tools directory). If the wave table files are found, they are expected to hold valid wave tables for the currently configured sample rate. If they are not found, internal wave tables are constructed each time MSS is started.

The wave table files are automatically created when MSS is built from source. If you need to regenerate the wave table files for a different sample rate, edit the Makefile in the tools directory and then run make in that directory.

Basic principles

The overall goal of MSS was to create a very flexible synthesizer. The supplied synthesizer module types (different kinds of oscillators, filters, envelope generators etc), plus the ability to create and interconnect arbitrary instances, plus the fact that each module type in itself has a number of parameters that can be independently adjusted gives you immense flexibility in creating complex sounds.

The following module types are available:

• WTOscillator. This is a wave table driven oscillator where the generated wave form is constructed additively by adding together partials with controllable amplitude and phase (as defined by a WaveTable). A WTOscillator instance may be frequency modulated by both low frequency oscillators (for vibrato) and tone frequency oscillators (for FM synthesis). The tuning of a WTOscillator instance may be set freely as a product of a parameter and the frequency of the triggering note, e.g 2.0 times the frequency of the triggering note. The gain of a WTOscillator instance may be envelope controlled.
• WaveTable. A wave table is defined by a number of partials with controllable amplitude and phase.
• PlainOscillator. This is an oscillator that produces any of the usual wave forms (triangle, saw, pulse etc.).  A PlainOscillator instance may be frequency modulated only by low frequency oscillators (for vibrato). Otherwise, frequency and gain control is the same as for the WTOscillator.
• AGOscillator. This is an asynchronous grain oscillator where the generated wave form is constructed according to the principles of asynchronous granular synthesis. For further information about asynchronous granular synthesis, see http://www2.hku.nl/~peter4/granindex.html
• WaveGuide. This is a wave guide oscillator where the generated wave form is constructed according to the principles of  waveguide synthesis. For further information about waveguide synthesis, see http://www-ccrma.stanford.edu/~jos/wg.html
• Filter. This is a second order filter with selectable filter type (LP, HP etc) and controllable relative cutoff frequency and damping. The filter cutoff frequency may be envelope controlled.
• SimFilter. This is a first order non-resonant filter with selectable number of filter sections in cascade. The only supported filter type is LP. The filter frequency may be envelope controlled.
• MFilter. This is a fourth order LP filter with controllable resonance. The filter frequency may be envelope controlled.
• BiquadFilter. This is a second order filter with selectable filter type (LP, HP etc) and controllable resonance. The filter frequency may be envelope controlled.
• AllPassFilter. This is an all pass filter with controllable gain and delay.
• MultiDelay. This is a 4 tap delay line with controllable gain and delay for each tap. The delay may be envelope controlled.
• LFOscillator. This is a low frequency sine wave oscillator intended for modulation of other synthesizer modules. The LFO may be used for modulating the frequency of a WTOscillator or a PlainOscillator, or the pulse width of a PlainOscillator generating pulse a wave form, or the frequency of any of the filters.
• Adsr. This is an envelope generator that may be used for envelope control of most module parameters, e.g filter frequencies and oscillator gain.
• PinkNoise. This is a source of pink noise with controllable gain.

For performance reasons, MSS makes a clear distinction between sample rate modules (sampled at a relatively high rate, typically 44100 Hz) and control rate modules (sampled at a lower rate, typically around 1000 Hz). Both sample rate and control rate are configurable, see  Configuration . Sample rate modules like oscillators, filters and noise generators typically work on the stream of samples output to the D/A converter.
Control rate modules are used for modulation of sample rate modules. Sample rate oscillators is a special case, they may be used either for producing the sample stream (as generators) or for frequency modulation in FM synthesis (as modulators).

The sample rate limits the maximum frequency that may be generated in the output to half the sampling frequency. The control rate limits the time resolution of the control signals generated by control rate modules. A control rate of 1000 Hz means that e.g Adsr envelopes have a resolution equal to 1 ms.

For more info about synthesizers in general, filter algorithms etc, see Links.

Using the synth

Getting started

Two windows will appear, one control window and one keyboard window. The control window shows the default synthesizer configuration (read from file moduleconfig).

The synth may be played either on the built-in GUI keyboard, or on an external MIDI keyboard. Module parameters in the current synthesizer configuration may be changed directly in the synth control window. The current synthesizer configuration (including the module configuration) may be saved to file, or changed by reading a new configuration from file.

The current synthesizer configuration may be changed by interactively creating/deleting synthesizer modules, or change their properties. Put the cursor on top of an existing module and use the popup dialog to add/delete modules or change their properties. The controllable parameters (see Module reference  for a listing of the controllable parameters for each module) may be changed directly in the control window GUI.

Real time aspects

Because of the real time scheduling, MSS also has a very brutal mechanism for load control built-in. The current CPU load is continuously monitored, and when the load becomes too high MSS simply stops all sample processing until the CPU load decreases. This will cause long dropouts every other second or so. You then have to release some notes or stop adjusting parameters furiously (or whatever you are doing) in order to be able to play new notes. This simple mechanism is just a safety thing that prevents the real time scheduled process from completely starving all other processes on your system, including the MSS GUI. If you play MSS via the GUI you want the GUI to respond when you try to release notes.

Module parameter settings & intermodule dependencies

These are the only restrictions imposed by MSS:

• A single output module always exists. You can't add another output module or delete the existing one.
• Intermodule connections must be compatible with respect to rate, i.e it is not allowed to connect a sample rate output to a control rate input or vice versa.
• A WTOscillator can't exist without a Wavetable.

Module configuration examples

Module reference

WTOscillator

The WTOscillator has the following controllable parameters:

• Tuning. This is a multiplier relative to the frequency of the triggering note. Setting tuning to e.g 0.5 means that the WTOscillator generates a wave form with a frequency equal to half the frequency of the triggering note.

• Gain control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• LFO Frequency modulation control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Frequency modulation control. This is a sample rate input that may be connected to any sample rate output (typically another WTOscillator or a PlainOscillator).

WaveTable

The WaveTable has the following controllable parameters for each partial:

• Amplitude.
• Phase.

PlainOscillator

The PlainOscillator has the following controllable parameters:

• Tuning. This is a multiplier relative to the frequency of the triggering note. Setting tuning to e.g 0.5 means that the PlainOscillator generates a wave form with a frequency equal to half the frequency of the triggering note.
• Duty cycle. This parameter controls the slope of the triangle wave form (if that wave form is selected) or the pulse width of the pulse wave form (if that wave form is selected).
• Choice of wave form. Parabola, variable slope triangle, saw, or variable width pulse may be selected.

• Gain control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• LFO Frequency modulation control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Duty cycle control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).

WaveGuideOscillator

The WaveGuideOscillator has the following controllable parameters:

• Tuning. This is a multiplier relative to the frequency of the triggering note. Setting tuning to e.g 0.5 means that the PlainOscillator generates a wave form with a frequency equal to half the frequency of the triggering note.
• NoiseCutoff. The waveguide is initialised with lowpass filtered noise.
• cx1 and cx3. The waveguide output is fed through a lowpass filter and then through a nonlinearity before being fed back to the waveguide input. cx 1 and cx3 define the nonlinearity.

• Gain control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).

AGOscillator

The AGOscillator has the following controllable parameters:

• Tuning. This is a multiplier relative to the frequency of the triggering note. Setting tuning to e.g 0.5 means that the PlainOscillator generates a wave form with a frequency equal to half the frequency of the triggering note.
• Grain envelope. This is a choice of different grain envelopes, e.g rect envelope or gaussian envelope.
• Envelope rate. This parameter controls the steepness of the envelope, e.g for a linear envelope the envelope rate is the rate at which the maximum amplitude changes linearly.
• Low freq & high freq. These are multipliers relative to the frequency of the triggering note. Setting low freq to e.g 0.5 and high freq to e.g 2.0 means that the AGOscillator generates grains where each individual grain has a frequency which is randomly distributed between half the frequency of the triggering note and twice the frequency of the triggering note.
• Grain density. This parameter controls the rate at which new grains are generated (no of grains per second).
• Grain lz. This parameter controls the product of grain density and grain length. For a given grain density, grain length is proportional to grain lz.
• Grain spread. This parameter controls the distribution in time of the randomly generated grains.

• Gain control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• LFO Frequency modulation control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).

Filter

The Filter has the following controllable parameters:

• Relative cutoff frequency. This is a multiplier relative to the frequency of the triggering note. Setting relative cutoff frequency to e.g 0.5 means that the Filter cutoff frequency will be equal to half the frequency of the triggering note.
• Damping

• Cutoff frequency control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Filter data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).

SimFilter

The SimFilter has the following controllable parameters:

• Relative cutoff frequency. This is a multiplier relative to the frequency of the triggering note. Setting relative cutoff frequency to e.g 0.5 means that the SimFilter cutoff frequency will be equal to half the frequency of the triggering note.

• Cutoff frequency control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Filter data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).

MFilter

The MFilter has the following controllable parameters:

• Relative cutoff frequency. This is a multiplier relative to the frequency of the triggering note. Setting relative cutoff frequency to e.g 0.5 means that the MFilter cutoff frequency will be equal to half the frequency of the triggering note.
• Resonance

• Cutoff frequency control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Filter data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).

BiquadFilter

The BiquadFilter has the following controllable parameters:

• Relative cutoff frequency. This is a multiplier relative to the frequency of the triggering note. Setting relative cutoff frequency to e.g 0.5 means that the Filter cutoff frequency will be equal to half the frequency of the triggering note.
• Q value
• Filter gain (only for some filter types)
• Filter slope (only for some filter types)

• Cutoff frequency control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).
• Filter data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).

AllPassFilter

The AllPassFilter has the following controllable parameters:

• Gain
• Delay

• Filter data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).

MultiDelay

The MultiDelay has the following controllable parameters:

• Gain (for each tap)
• Delay (for each tap)
• Feedback

• Data input. This is a sample rate input that may be connected to any sample rate output (typically a WTOscillator or a PlainOscillator).
• Delay control. This is a control rate input that may be connected to any control rate output (typically an LFOscillator or an Adsr envelope generator).

LFOscillator

The LFOscillator has the following controllable parameters:

• Frequency
• Gain

• Gain control. This is a control rate input that may be connected to any control rate output (typically another LFOscillator or an Adsr envelope generator).
• LFO Frequency modulation control. This is a control rate input that may be connected to any control rate output (typically another LFOscillator or an Adsr envelope generator).

Adsr

The Adsr has the following controllable parameters:

• Envelope type. The envelope type can be a Log envelope (gain increases logarithmically as a function of time), a Lin envelope (gain increases linearly as a function of time), or an Exp envelope (gain increases exponentially as a function of time).
• Gain
• Start level
• Stop level
• Velocity sense. A velocity sense of zero means that the envelope is independant of velocity.
• Attack time
• Decay time
• Sustain level
• Release time

PinkNoise

The PinkNoise module has no controllable parameters.

The PinkNoise module has the following inputs:

• Gain control. This is a control rate input that may be connected to any control rate output (typically an Adsr envelope generator).

Comments & questions

I have worked on MSS now and then over a rather long period of time just for the fun of it. Implementing a powerful software synthesizer is a great challenge, it certainly demands knowledge in some diverse areas: Sound synthesis algorithms (how to generate sounds), software architecture and design (how to design a sufficiently flexible and efficient software system), GUI design (how to present a usable interface) and, last but not least, efficient implementation of real-time software.

Is there anybody out there interested in improving e.g the GUI ?

Debugging & bug reporting

MSS provides some debugging options that may help in identifying problems running MSS.

Using the option -mididebug gives a printout of each MIDI message received via the MIDI input port. All messages are printed, although only the "NOTE ON", "NOTE OFF" and "PITCH WHEEL CONTROL" messages are actually implemented. If you have a problem using your external MIDI keyboard with MSS, please start MSS with the command './runsynth -mididebug > mylog', then hit a few keys on the keyboard and send me a mail including the resulting log file 'mylog'.

Using the option -debug gives a verbose printout of MSS internal information. If you have a problem using the builtin keyboard (the keyboard window) with MSS, please start MSS with the command './runsynth -debug > mylog', then hit a few keys in the keyboard window and send me a mail including the resulting log file 'mylog'.

If you think you have discovered a bug in MSS, please notify me via mail to mats.olsson@chello.se.

Links