RTSynth  v1.9.0

News
Midi Events
Main Panel
String Synth
Flute Synth
Audio Effects
 
 
 

Intro

Goal of the software is to reproduce sounds of strings, organs, flutes and drums in real time. The sound generation is based on the physics of the instruments. That means all sounds created by this software are the result of a mathematical model based on some physics about how the sounds shape varies in time. You have access to most of the models parameters through a graphical interface. Further more most of the parameters can be controlled by MIDI controllers.
 

The intro of version 1.6.2 is some years old and CPU performance has increased alot. RTSynth is now developed on an AMD Athlon XP1700+ based PC. Here are some benchmarks for the effects measured on my machine:
 

And yes i tried the above number. My machine can play even more than the given 12 complete effect panels;)
Anyway from the numbers above RTSynth should still be usable on a Pentium 200 like system.
 

Intro from old version 1.6.2

To perform well, RTSynth should be set to userid root with `chown root RTSynth; chmod +s  RTSynth`. This will allow RTSynth to use the real time scheduler for best run time behaviour. After getting the scheduler RTSynth is setting back its root priority to the normal users one.
 

To make the choice of the MIDI input source as flexible as possible, RTSynth can read midi events from a input stream. This can be a device, a pipe (stdin) or a named pipe (fifo).

Possible command line invocations:

   RTSynth                                 normal execution. Reading midi events from /dev/midi00.

 output options:

   RTSynth  --output=/dev/mydev
   or
   RTSynth  -o /dev/mydev   use the given audio output device (must be a OSS /dev/dsp compatible device).

 input source:
 

   RTSynth --input=/dev/midi

   RTSynth -i /dev/mido
   or
   RTSynth </dev/mymidi    to read from a given midi device

   RTSynth <fifo

   cat  foo  | RTSynth               to read midi events form a fifo or pipe.
 
 

I have tried to use EsounD as an alternative audio output destination, but the current version of esound does not support real time audio. To be more detailed, the audio stream esound opens for RTSynth to write to does not offer a constant rate of samples per second like the /dev/dsp device. Maybe ALSA will become the future of audio and midi subsystems for Linux, but I did not take a closer look on it so far, maybe when upgrading to linux 2.2 ...

If you don´t have a midi keyboard (like I am) or any other external midi equipment, you can use clavier to put you computer keyboard into a midi one. The necessary command lines to connect clavier with RTSynth would look like:

   mkfifo   /tmp/midififo
   RTSynth </tmp/midififo
   clavier -o /tmp/midififo

or you can use SoftWerk a cool software "analogue" sequencer to trigger RTSynth.
 
 

Known bugs: Overdriving the PM-resonator effect to hard may crash the effect. You have to restart RTSynth to get it work again. The flute synth may also crash when using some extreme settings. Loading of corrupt patch files may break down RTSynth completely.
 
 
 
 

News (not complete)

         The blue edition reached another milestone on its way to version 2 -> version 1.9.0.

• In this version more physics can be applied to the sounds by the use of an improved physical modelling resonator.
• Eleminated stabilitiy problems. No more wild going flute sounds or drums that kick out their resonators.
• Highly improved PM-resonator effect. This multi resonator adds a body to your sounds and can also add some non linear effects of the body which depends, like with real instruments, on the playing loudness. Updated documentation about this effects as it is the most important (physical) one.
• The maximum number of voices has been increased to 32.
•  Preset sounds have been updated. NOTE: The presets are for a sample rate of 44100Hz and may not sound as well on other rates.

Version 1.8.0

      New release version 1.8.0 (code name "blue") is available for download.

      "Renovated" the quite old DSP core a little bit to fit to modern CPUs by removing lookup-tables and replacing approximations by their exact formulas.

         Benefits.

• The application is not bound to a fixed sampling rate anymore. As there is still some work to do in the effect section the supported range is for now limited to the range 44100-48000 Hz.
• Audible increase of overall tuning.
• The string synth has now the long missing pitch bend with a selectable range of +/- 0-4 half-tone steps. A step size of zero will switch back to the old behaviour. (pitch-wheel -> filter) NOTE: As this is a somewhat CPU intensive task you should switch pitch bend only to on when you really need it!

• Eats some more CPU cycles ;-)

Version 1.6.8

• This version is for ALSA version 0.9.
• Added command line option to set the audio fragment size.
• Added small configuration dialog.
• Improved tracking of pitch-bender in string and flute synth.
• Added optional "auto pan" mode.
• Added support to control synth parameters by MIDI controllers.

Version 1.6.2

            BugFix: eliminated problems with reading from /dev/midi on linux 2.2.x based systems.

Version 1.6.2

            BugFix: eliminated problems with reading from /dev/midi on linux 2.2.x based systems.

Version 1.6.2

            BugFix: eliminated problems with reading from /dev/midi on linux 2.2.x based systems.

            Changed handling of midi NoteOff events -> eliminating possible multiple playing of the same note.

            Added new main-panel. You can now run several synth-/effect-modules and connect them together.

            Improved and scale-able reverb effect.

            Some minor bug fixes and runtime optimizations.
 
 

Version 1.6.0 is the first glibc based version. Advantages over the older 1.5.x versions are:

RTSynth now always runs in real time mode. The problems with reading midi events from a pipe are solved by using threads.
RTSynth now works fine with the "SoftWerk" software sequencer program.
New features are a peak load meter that monitors the CPU/system load from the view point of RTSynth.
A auto switch off function on a system overload or audio underrun.
The output filter frequency (string synth) and the embouchure size (flute synth) are connected to the midi pitch bend for real time control by a external device.
Some buildin preset sounds (instrument and effect).
added command line optiion for audio output device.

Midi Events

• NoteOn (includes velocity)
• NoteOff
• AllNotesOff
• AllSoundOff
• AllCtrlOff
• ProgramChange   - selects a preset sound.  (not available in version 1.6.2)
• PanPosition
• HoldPedal   - only available when the string synth is set to 24 voices.
• Volume
• PitchBend   - The filter/embouchure value given by the interface slider is multiplied by two on max pitch bend and zero on min pitch bend. A centred pitch bend leaves the slider value unchanged.
• Support for midi "running status" used by some sequencer programs like CuBase.

Main Panel

With in the main panel you can:

• Create, control and connect audio modules
• Change the audio buffer size
• Save the machine state (not yet implemented)

Every Synth- and Effect-modul is represented by a tile:

You can set the midi channel and switch on/off a audio module directly from the tile by using the control elements shown in the picture.
Pressing the left mouse button on the audio output symbol and dropping it over the target tile will build a connection. Doing the same process between already connected modules removes the connection.
Left/right mouse button over the midi channel field decrements/increments the channel value.
Circular connections between modules are not allowed and will be rejected by the program.
Pressing the right mouse button opens a context menu.

Any module with a output that is not explicitly connected to another one is connected to the main output by default.
 

String Synth

(back)
as the name suggests this synth is mainly designed to produce string like sounds. But it is not limited to that. You can also use the string synth for example to produce a sinus wave sound or together with the resonance able low pass filter some cool synthetic sounds. It is a polyphonic synthesizer with up to 24 independent voices based on the so called `physical modelling synthesis´. Because the base algorithm does not have much to do with the physics of a real string instrument (the interaction between the string, the instrument corpus and the players fingers are much to complex to be calculated on a PC in real time), I call it the `energy dissipation model´. The maximum number of playable voices of course depends on the speed of your machine, synthesizer settings like filters and the number and type of activated audio effects.

To become familiar with the synthesizer settings you may try out some of the synth voices included in the archive. A small example starting with a synth produing a sine wave, as mentioned above, and then modifing it to went into a "SynthBass" sound is given here:

1. We want a clean sinus wave -> Wave ampl. = 1, Wave type = sin.
2. The sine wave should have a constant amplitude. This is meet by setting all damping parameters in the Energy dissipation panel to "no damping" -> frequency = 1, freq max = 1, filter follows note = no, feedback = 1, filter attack = 0, off-delay = 0. It is a little bit hard to set the feedback to a value of exact 1.00, soft damp. can help in do it for you by setting it to a value greater zero.
3. Normally a sinus sound needs no output filter but as you can hear on some notes there is some noticeable distortion. To reduce it we use the Output filter with filter follows note = lin, frequency = 1 (filter any frequency higher than the base octave), bessel, 12 dB. You may also use a small resonance value (0.1) to get a even sharper filtering.
4. Now, we want to apply a conventional amplitude envelope to the sinus wave to get a short percussive sound. The Output filter envelope can be used for that -> env mode = normal, env ampl. = 0 (we don't want a filter sweep), env speed = 1 (fastest attack), env sustain = 0 (no sustain at all), env release = 0.2 (short sound). And last but not least in the Output and note controlpanel the ampl-env must be activated.
5. We modify the sound now a little bit. For the wave type we choose an unfiltered rectangular wave (crect) an apply an output filter envelope by setting env ampl. to 1.4 and to make the sound a bit more interesting we apply a value of 0.3 to the output filter resonance. To apply note velocity to the filter sweep amplitude we switch the env mode to accent., to ampl. if we want the note volume to be independent from the note velocity, and to speed if our intention is to modulate the envelope speed by the note velocity. To have a sustained sound again we can switch the ampl-env off.
6. to produce a more string like sound we switch the output filter to off, the ampl-env to off. Set the Wave ampl. to 0.5, the Random filter frequency to 0.53, its filter follows note mode to "cool" and let Energy dissipation do the decay stuff by setting: frequency = 0.68, freq max = 0.89, filter order = 1, filter follows note = "cool". To have a slowly decayed sound off delay = 30, off-feedb. = 0.998 for example can be set.
7. now we switch the Output filter on again to have a some what different "SynthBass" sound than in Step 5.
 
 
 

The String Synth panels:
The string synth panel is subdivided into smaller panels sorted by functionality.

Energy dissipation

This together with Random Filter and Additional wave is the "heart" of the synthesizer. Here you can set the parameters for the time dependent behaviour of the oscillator like frequency dependent damping, cut off frequency ...

Random filter

The random filter is used to filter the noise source output and may also be used to filter the output of the additional wave. The filtered random noise together with an additional wave are used to initialize the oscillators starting wave form. The usage of a random noise amount to produce a wave form makes the sounds generated by the string synth quite different form the static sounds generated by sample based synthesizers. Like for a real string instrument the produced sound will never be exact the same even when playing the same note.

Additional wave

In addition to the noise source the output of the additional wave unit can be used to build the starting wave form. This panel includes a mixer for the balance between the random noise and the additional wave amplitude.

Output filter

Here the generated wave can be filtered by a resonance able low pass filter.

Output filter envelope

Settings for an output filter and/or amplitude envelope can be done here. Each String Synth voice has only one envelope generator but it can be used for output filter and amplitude modulation.

Output and note control

Sound volume, amplitude attack, decay, amplitude envelope and more can be set here.

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Flute Synth

(back)
This is a monophonic synth. It implements the ´base clarinet´ and the ´base flute´ algorithms with some small extensions and modifications. Since version 1.8.0 the flute synth has become really usable. The tuning is now fine and instabilities as found in older versions have gone away ;)

Oscillator settings

Breath

Pressure - tremolo

Output filter

Output control
 
 

Audio Effects

(back)
RTSynth has seven hard wired audio effect units.

Effects in order of their connection:

Distortion

The distortion effect has a soft mode, emulation of a tube like distortion, and a normal mode for a transistor like distortion.

Universal filter

This universal filter can be used as a LP, HP or BP filter. The filter order can be set from 6 dB to 24 dB. It also supports a simple filter sweep function.

PM resonator

The PM resonator gives you the possibility to add a "body" to your sounds. It is a multi resonator with a non linearity on higher input levels. As you can see from the "PM resonator" panel/table, this effect has alot of settings to play with ;) Just as in real life you can tune the PM resonator in such a way that some notes will sound "dead", so be careful ... but usually the PM resonator is a good friend in making your sounds more reach and full.
Please use one of the settings from the presets as an starting point to get somewhat familiar with this effect.
 

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Resonator

This is an equalizer with a bank of five band pass filters.  Setting a filter to a value of zero disables this filter and therefor saves CPU time.

Chorus

The well known chorus effect.

Reverb

A simple reverb effect. In stereo mode two reverbs, one for each channel, can be mixed to give a more complex effect.

Delay

The delay effect can operate in stereo mode to give a ping-pong like effect.
 
 

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