You are here

Applied Acoustic Systems Tassman v1.2

Physical Modelling Synth By Martin Walker
Published July 2000

The Player creates an attractive front‑panel display for the collection of modules you have used in your instrument. This is an analogue model using an LFO to drive twin step sequencers on the top row, with twin VCO/VCF/VCA sound‑producing chains beneath.The Player creates an attractive front‑panel display for the collection of modules you have used in your instrument. This is an analogue model using an LFO to drive twin step sequencers on the top row, with twin VCO/VCF/VCA sound‑producing chains beneath.

Physical modelling may be fashionable, but it isn't always very controllable. AAS aim to change all that for PC owners, by equipping their Tassman software synth with an easy‑to‑use front end. Martin Walker enters a new world of generators and resonators." target="_blank" csover="B56BB46515" onmouseover="CSAction(new Array(/*CMP*/'B56BB46515'));return true;The Roland D50 and Korg M1 spearheaded a new era of Sample + Synthesis sound generators that provided much more realistic acoustic sounds than the analogue and FM designs that preceded them. However, the samples they rely on are still only static renditions of the real thing, and such designs aren't capable of the range of expression available on any acoustic instrument. The only way to improve matters is to analyse the way acoustic instruments make their sounds, and find a way to duplicate this more closely. This technique is termed physical modelling, and uses complex mathematics to simulate the behaviour of standing waves in a stretched string, down a tube, in a chamber, or in a plate. These objects are normally termed resonators, since they don't produce any sound by themselves. Instead, just as you need to pluck a guitar string, hit a piano string with a hammer, or blow a flute, you need to excite the resonator in some way, using a 'driver'.

Commercial physical modelling synths using these techniques first appeared in 1994, with Yamaha's VL‑series instruments. These used physical models to create realistic wind and stringed instruments, and were made even more expressive by the use of breath controllers capable of generating data from several MIDI controllers simultaneously. The first affordable keyboard‑based instrument using physical modelling was the Korg Prophecy, released in 1995, and Korg followed this in 1997 with the first major release of a polyphonic synth featuring physical modelling — the Z1.

However, as far back as 1996 physical modelling was also beginning to appear inside PCs, when Creative Labs first showed its AWE64 Gold soundcard (reviewed in SOS July '97). This included WaveGuide synthesis, effectively an early soft synth that added 14 extra physically modelled instruments to its SoundFont engine. It was developed for Creative by Seer Systems (the brainchild of Dave Smith, who created the Prophet synth), and the same WaveGuide technology later resurfaced in their rather more ambitious Reality soft synth (originally reviewed in SOS November '97). This has evolved into a powerful system that includes analogue and physical modelling as well as FM and modal synthesis. However, although the 20 algorithms in its latest version are capable of a huge variety of sounds, each one is comparatively limited in its range of sounds, and producing radically new ones is simply not possible unless Seer create further algorithms in a future release.

Which brings us rather neatly to the product under review here. Tassman goes one stage further than Reality, by providing a modular approach to physical and analogue modelling, and is therefore capable of a much wider variety of sounds. The strength of Tassman lies in its flexibility, since you can assemble instruments from any combination of 14 resonators (in the current release) and five different drivers, as well as adding many traditional synthesis features such as filters, envelopes and step sequencers. Great attention has also been paid to the user interface, to provide a graphically familiar and easy‑to‑control front end.

Playing Parts

The Builder is very easy to use, although it would take considerable practice to get your patch cords as neat as this. The instrument shown is the electric guitar: you can see the plectrum and string modules sandwiched between the differently coloured Polykey and Polymixer, followed by a pickup and various effects.The Builder is very easy to use, although it would take considerable practice to get your patch cords as neat as this. The instrument shown is the electric guitar: you can see the plectrum and string modules sandwiched between the differently coloured Polykey and Polymixer, followed by a pickup and various effects.

Tassman actually consists of two separate applications which can be run independently. Tassman Player is, as the name suggests, used to load in predesigned synth setups and turn MIDI input into sound, while synths are constructed and edited using the stand‑alone Tassman Builder program. Tassman Builder saves its instruments as text files with a '.mom' extension, and the contents of these are used by the Player to generate a very attractive front‑panel display based on the modules you have used in your design, as well as to generate the code necessary to play the instrument.

Most modules present in your design will appear in the Player as components of this front panel, and can be given a suitable title. The Player graphics mimic a rack that can hold up to three vertically stacked rows of modules, although you can design synths with up to eight rows, and display any simultaneous combination of three using the eight numbered buttons at the bottom of the Player window. The Player window has a fixed size, so complex rows containing lots of modules may extend horizontally beyond its visible area. If this happens you can click on any blank area of the panel in question, whereupon the mouse cursor changes to a hand, and the panel can then be dragged to the right or left to view its extremities. This system works well, although a standard sizeable window with horizontal and vertical scroll bars would perform the same function, and in many cases would also let you see the entire panel area simultaneously without the complication of shuffling combinations of three rows.

The horizontal position of each module is determined by its horizontal position in the Builder window relative to other modules in the same row. However, many of the modules in the In/Out category of the Builder window, like internal mixers, constant values, pitch and modulation wheels, remain invisible in the Player, since they need no front‑panel controls.

The Player titlebar displays the instrument and current preset names, and clicking on the Tassman logo alongside allows you to set up its MIDI configuration. You won't need this if you are using any of the step sequencer instruments, since these have their own internal clock, but you will need to choose which MIDI input you use to play your synths when triggering them from an external MIDI keyboard. If you want to run Tassman from a MIDI sequencer you will need to use a utility like Hubi's Loopback, and choose one of its MIDI nodes to link the two.

There is a known MIDI bug in the initial release version: Tassman 1.2 alphabetically sorts the list of MIDI input devices, and shouldn't, so that the name you click on probably won't choose that device. The other limitation is that you cannot choose your audio device from within the application — it instead uses the preferred Windows playback device, as set in the Multimedia applet of Control Panel. However, both of these issues have already been resolved by a software patch. The beta version of this worked perfectly in my PC, and the official version should be available on the AAS web site by the time you read this. With the Player updated, an additional Audio button appears beneath the MIDI one, and lets you choose any MME or DirectSound driver installed on your PC.

Four additional buttons along the bottom left of the Player let you load and save presets, store new ones using the Save As button, and undo the last control movement. You can also save and load presets for individual modules by clicking on the down and up arrows in their bottom left‑hand corners: this is particularly useful in the case of sequencers, when you have painstakingly set up a set of melody lines (more on this later).

The controls themselves are easy to adjust: after you click on one to select it, the relevant module name is displayed at the bottom right of the Player window, with the name of the parameter beneath, and the current value of the control is displayed in a natty scrolling 'combination lock'‑style readout alongside. To change the current value you can either drag the mouse up or down, use the arrow, Page Up, or Page Down keys, right‑click at a knob position to instantly set it there, or use the third central button provided on some mice to move slowly to the desired set position. Some controls, such as pitch modulation, have a central default position to provide accurate keyboard tracking. These have a green arrow LED above them that illuminates at the default setting, and you can left‑click this directly to return it to this position.

Building Blocks

Once you understand the basics you can build models as large as your processor is able to power. This is the Octopus, featuring seven sequencer‑driven analogue chains, and an eighth which uses a mallet and membrane construction to provide a bass drum backing.Once you understand the basics you can build models as large as your processor is able to power. This is the Octopus, featuring seven sequencer‑driven analogue chains, and an eighth which uses a mallet and membrane construction to provide a bass drum backing.

If you don't want to get into the business of designing your own synths, you could simply use the Player with the 88 supplied designs (see the Sound Examples box for details of some of these). However, the majority of users will want to try designing their own synths, for which the stand‑alone Tassman Builder application needs to be launched. However, before you can hear anything you have to launch Tassman Player from the Builder menu (or using the Ctrl‑T shortcut).

Tassman Builder's single resizeable window is divided into three main parts. Most of the window is taken up by the construction area, which is where you assemble your synth using modules from the library. The library resides on the left‑hand side, and displays any one of seven categories of modules: Generators, Resonators, Filters, Envelopes, Effects, In/Out, and Sub‑Patch. When you click on a category to activate it, a selection of buttons appears in the lower part of the library area. Each one corresponds to a single module, and its name appears if you hold the cursor over it.

A single click of the mouse selects a module, whereupon the Help window above the construction area displays more information about it, such as a description of its controls and how best to connect it. Once a module has been selected you move your mouse into the construction area, where it changes into a crosshair display to help you place the module in a suitable position. Another mouse click drops it into the construction area. Clicking on any module already in the construction area selects it (a red outline box is displayed around it) and you can then click and drag it to another position if required, while Ctrl‑clicking lets you select multiple modules.

Modules have a number of inputs down their left‑hand side, and a number of outputs down their right‑hand side to allow you to connect them together: once again, holding the cursor over an input or output displays a text description of the connection. To connect one module to another, you click on one of its output terminals with the mouse, whereupon the cursor changes to a tiny jack plug. You can now drag this in any direction and left‑click again over the input terminal you want to connect it to. This will create a patch cord with suitable right‑angle bends to reach its destination neatly. If you want to decide on your own route for the cable, you can left‑click at any point to create a 'break point' where you can change direction from horizontal to vertical or vice versa. Existing patch cords can also be deleted or their paths edited.

You can tidy up your array of modules at any time while designing a synth, by selecting any number of them and using either the H‑Align or V‑Align commands from the main menu to line them up. This certainly helps to keep things clear, although it's still fairly easy to create a rat's nest of cables if you don't take some care during the design process. Thankfully there is a multiple‑level undo function, which makes editing less stressful.

Many of the modules are fairly self‑explanatory. Each synth needs a DAC (Digital to Analogue Converter) module from the In/Out category to connect its output to your soundcard, and the simplest sound source to use is a VCO (Voltage Controlled Oscillator) from the Generators category. Once you connect the output of the VCO to the input of the DAC you have a simple working synth.

The arrangement of the modules that appears in the Player's front‑panel display is controlled from the Builder by double‑clicking the appropriate module in the construction area. This opens up a dialogue window where you can choose a new module name that appears at the top of the module in the Player window, and also decide in which row it will be displayed in the rack. Depending on which module it is, you can also enter new default values for some of its controls that will appear when the Player is first launched, and such things as the number of notes in the PolyKey modules. You can also link any front‑panel control to any external MIDI controller for adding expression.

Down At The Library

The physical models have easy‑to‑use front‑end controls. This simple instrument is formed from two series‑ coupled plates driven by a Noise Mallet, but is still capable of a wide range of sounds from gongs to metal marimbas.The physical models have easy‑to‑use front‑end controls. This simple instrument is formed from two series‑ coupled plates driven by a Noise Mallet, but is still capable of a wide range of sounds from gongs to metal marimbas.

A total of 72 modules are included in this initial release (you can find a full list in the Modules box). Many of them are standard hard‑ and soft‑synth fare, such as the VCO and LFO in the generator category, all eight filter types, and the ADSR and VCA in the envelope category, and as such will already be familiar to most musicians, so I'll concentrate on the rest. The majority of effects are also fairly recognisable, even if they are sometimes generated by unusual means, such as the reverb modelled from three connected tubes.

The In/Out category, while considerably bigger than the others, still holds many basic and easily understood modules. There are Mixers to combine various numbers of signals, interfaces to controllers such as Pitch and Modulation wheels and damper pedals, and Player and Recorder to input or output WAV files. Also included in this category are various Inlets and Outlets to create Sub‑Patches, a feature that can save the experimenter a lot of development time. A Sub‑Patch either has an Inlet module on the left, or an Outlet module on the right, or both, and these are connected to a collection of other modules. Once you have designed a Sub‑Patch, it is saved with a '.hom' file extension rather tha n the normal '.mom' one, and can be imported at any time into the Sub‑Patch module category and included in your design. It then behaves just like any other module, and can be wired into complex instruments to save both time and space. The supplied Lib folder includes 22 Sub‑Patches including an effect rack, ensemble, stereo chorus, stereo pan, and hall echo.

Two forms of input controller are catered for. If you want to play your instrument from a MIDI keyboard there are four types of Keyboard module: Keyboard provides a monophonic output with high‑note priority (just like most monosynths), while Vkeyboard does the same but with added velocity sensitivity. To create polyphonic instruments you need to choose either the Polykey or Polyvkey modules. You can select the number of voices in their Properties boxes (between 2 and 24, depending on how much processor power you have and the type of instrument you are creating), and you will also need a Polymixer module at the other end of your sound‑producing section, to combine the voices before any further processing. You add keyboard control by connecting one of the four keyboard modules to your synth, attaching its output pitch signal to the frequency modulation input of an oscillator, and its gate signal to something like an ADSR envelope generator connected to a VCA.

The second form of control is the Sequencer module, a 16‑step looped device with a small graphic keyboard for editing purposes. Up to four banks of eight sequences can be saved in each preset; you step through the selected sequence by hand and either enter a rest or any note in a five‑octave range. Although you can't chain different sequences together, you can switch between them smoothly during a real‑time performance, and by programming multiple sequenced lines into a sequencer preset you can provide complementary sequences to run across multiple voices in an ensemble.

Modelling Agency

It's the physical‑modelling aspects of Tassman that will intrigue musicians the most, and thankfully they are just as easy to use as the analogue‑modelling ones.

Generator modules such as the Mallet, Noise Mallet, and Plectrum can make noises by themselves. Each has a Strength knob to control the force of impact, and a Stiffness one to vary the sound from a dull thud to a tight click. A manual Trig button is also provided on the module panel if you are not using a sequencer or MIDI keyboard as an input.

The output of these Generators is normally connected to the input‑force signal connection of a Resonator, such as a beam, marimba, membrane, plate, or string. These physical models all produce quite different sounds, and you can adjust such parameters as their length (and width in the case of the membrane and plate), fundamental frequency, inharmonicity (to detune string partials at higher frequencies), the decay time associated with damping, and the number of modes used to simulate the object. The Excitation point determines where the object is hit by the generator, and the Listening point where the sound is picked up.

However, they all use a common Multimode front panel. Its Amplitude knob controls output level, while the Decay knob varies the amount of damping to simulate materials such as wood (short decay) through to metal (long). A Mod knob lets you modify the pitch using another signal, and the Damp/Freq control varies the damping depending on frequency — at one end you can simulate steel or glass, where high frequencies ring much longer than low ones, while in the neutral central position the material behaves more like nylon, and at the far end of its travel more like wood, where low frequencies ring longer than high ones.

The other major class of Resonator is Bowed Multimode, which encompasses Bowed Beam, Bowed Marimba, Bowed Membrane, Bowed Plate, and Bowed String modules. Once again these all have identical controls: in addition to those present on the Multimode front panel there are knobs for Force, Velocity, and amount of random bow Noise. The velocity and force signals for the bow would normally be created by an ADSR envelope, but you can also use a MIDI controller such as a mod wheel, which actually feels more natural than you might think.

You can create a huge range of plucked, struck, and bowed sounds by simply attaching a Generator to a Resonator, but to build more realistic acoustic instruments you can connect additional resonators to provide sympathetic resonances, such as those provided by the soundboard of a guitar or violin. For instance, by attaching two plates in series but leaving the pitch of the second one fixed you can create pitched gongs with a small amount of sympathetic resonance for more realism, while reducing the amount of pitched signal and fading up the sympathetic vibrations gives the effect of striking a small gong in various places on its surface.

There are also various more specialised physical models such as the Flute, which has Noise control for the amount of air in the sound, Labium for the position of virtual 'microphone' relative to the blowhole, Sharpness for the thickness of its edge, and Tone to control the air jet behaviour. Organ models a small polyphonic pipe organ, with Noise, Tone, and Labium controls, while Pickup simulates the function of a magnetic‑coil pickup as used by guitars and electric pianos, and can be positioned relative to the vibrating object with its Symmetry and Distance controls.

The only limitation I found in the current models is that, apart from the VCO, none of the other Resonators has true pitch‑bend capability — instead the bend jumps in semitone steps. Of course this doesn't matter with most physical models such as beam, marimba, membrane, plate, and flute, but it does currently limit the expressive capabilities of the string module. It is apparently part of the current coding optimisation, since changing pitch in a smooth manner would require recalculation of the entire structural characteristics of the model at each point, but AAS told me that they hope to add this facility in the next release.

In Use

The first few times you fire up the Player and find plenty of LEDs flashing but no sound, it's tempting to think that there's something amiss, until you remember to click the DAC module switch to its On position to turn on the soundcard output, and load up a preset. Without these two steps nothing will emerge from the output.

There are 88 instruments supplied with Tassman, and each has a number of associated preset files. One thing in particular struck me while auditioning these: many of the physically modelled designs are capable of a far wider range of sounds than you might initially expect, especially when changing the 'building material' from glass to wood can be as easy as turning a knob on the front panel. The analogue synths are also as versatile as you care to make them: the VCO has a flexible set of noise, sawtooth, pulse, and sine waves, along with pulse‑width modulation, while the filters sound suitably squelchy if required. However, the beauty of Tassman is that you can mix and match your modules to produce new hybrids as well, such as metal‑plate percussion driven from a step sequencer, or a flute whose pitch is controlled from a sample and hold module, but still played from a keyboard.

There are four well‑written Tutorials in the electronic and printed manuals to help get you started. The first covers the design of a complete 'analogue' synth with VCO, LFO and VCF, while the second adds keyboard control, VCA, ADSR, and MIDI control. The third covers Sub‑Patches and the step sequencer, and the fourth explores the basics of acoustic objects. Together they give you enough experience to start building your own designs, and then you're hooked!

Designing your own synths is rewarding, although I initially found the patch‑cord connection system rather unwieldy, and personally much prefer the elastic‑band system used by NI's Reaktor, which redraws itself if you later need to move the modules. However, there's no denying that the AAS system looks the neatest once you get the hang of it, even if it makes major structural alterations rather a nightmare.

Having to launch the Player each time you audition a change in the Builder can be tedious, and I hope that this aspect will become more streamlined in future releases. I suggested to AAS that instrument presets be incorporated into the instrument '.mom' file so that they can be chosen from a simpler drop‑down patch list, rather than needing to be loaded in separately, and they thought this a good idea for a future release, since a self‑contained instrument/preset file would also make swapping sounds over the Internet far easier.

Instruments using step sequencer modules are self‑contained, and you can use the Recorder module to capture their output to a WAV file if required. There are currently no built‑in sync facilities to clock these using an external sequencer application, but I still found it fairly easy to replace the LFO modules clocking the sequencer with a keyboard module, so that I could step them using external Note On commands; this isn't ideal, but it works.

Processor usage obviously depends on how complex your designs are, and in the case of polyphonic ones, how many voices they have. Tassman uses the same system as Reaktor in that overhead for each voice is allocated on creation, rather than during use. This means that the full overhead for the full number of voices will be taken when you first launch the instrument, however few notes you are actually playing. It provides no CPU meter, but of course you can use Microsoft's System Monitor to keep an eye on overhead.

The main limitation with this first release is when playing instruments in real‑time from a MIDI keyboard, since Tassman 1.2 has a fixed 1024‑sample buffer, meaning that its latency is fixed at a rather high 23mS, whether you use MME or DirectSound drivers. For a synth that models acoustic instruments this does make real‑time playing very unresponsive. However, AAS are giving a lower‑latency driver high development priority, along with support for DirectX and VST Instrument formats, and are hoping to release this as an upgrade in August, along with more acoustic models.


Tassman is an ambitious product, and already achieves a great deal in this first release version. It goes beyond Seer Systems' Reality in providing far more control over each physical model, and unlimited ways to connect the different mod ules. This will appeal to those who fancy exploring new designs of 'acoustic' instrument, although it's surprisingly capable in the analogue department as well. In fact, some of the most interesting possibilities come from amalgams of the two, where acoustic sources are driven from step‑sequencer front ends.

Those who want to explore the virtual recreation of existing acoustic instruments will also find plenty to keep them busy, but, just as in the real world, producing believable results tends to require complex models as well as a player capable of supplying suitable expression in their performance. Many of the supplied instruments such as the electric pianos and guitars, hammered dulcimer and flute sounded realistic even in my untutored hands, but others such as the acoustic guitar and drums weren't so convincing, although still quite usable.

The Player interface is elegant and easy to control, which is quite unusual for a system using physical modelling, and taken overall Tassman 1.2 is an impressive achievement. Moreover, judging by the lengthy discussions I had with its developers I expect it to mature into an even more powerful one in the months ahead.

Sound Examples

A huge number of pre‑constructed designs are included with Tassman, and these cover a large amount of ground sonically, from relatively straightforward virtual analogue to the weird and wonderful. They are arranged in three main folders labelled Acoustic, Analog, and Miscellaneous. Here are some of my favourites:

  • Arnold: an analogue additive 12‑oscillator monophonic synth capable of anything from sci‑fi meanderings to weaving bagpipes to emotive chord clusters. The name is a reference to the 12‑tone system of classical composer Arnold Schoenberg.
  • Eguitar: a versatile instrument with clean, jazz, and nasty presets, using a plectrum and string model followed by an electric pickup. By contrast, I found the Aguitar acoustic version rather disappointing.
  • Epiano: wonderful touch‑sensitive Fender Rhodes and Wurlitzer pianos with separate control of hammer, tine, tone‑bar and pickup position, complete with stereo tremolo.
  • Minitass: this Minimoog recreation is available in both monophonic and four‑voice polyphonic versions, and its three oscillators per voice provide a rich, fat sound. The filter doesn't have keyboard tracking, although this is easy enough to add.
  • Organ: a street pipe organ with lots of 'chiff' potential. It won't be what a lot of musicians expect, but is rather charming all the same.
  • Oscillotron: looped rhythmic motifs played by eight sequencer‑driven mallets and strings that sound like a cross between tribal drums and machines from Muppet Labs.
  • Troll: short quirky sequences of metallic, marimba‑like sounds created by a combination of a plectrum and beam. The sequences run continuously, but can be changed in pitch using a keyboard.

Tassman Modules

Tassman modules are divided into seven main categories:

  • Generators: Mallet, Noise Mallet, Plectrum, LFO, VCO.
  • Resonators: Beam, Marimba, Membrane, Plate, String, Bowed Beam, Bowed Marimba, Bowed Membrane, Bowed Plate, Bowed String, Tube, Tube4, Flute, Organ.
  • Filters: Lowpass1 (6dB/octave), Lowpass2 (12dB/octave), Vlowpass2 (variable 12dB/octave), Bandpass2, Sbandpass2, Vbandpass2, Highpass1, Comb.
  • Envelopes: ADSR, VCA, Volume, RMS, Portamento.
  • Effects: Reverb, Panpot, Delay, Flanger, Scratcher, Pickup, Divider, Inverter, Shifter, Sample and Hold.
  • In/Out: Keyboard (four variants — monophonic and polyphonic with and without velocity sensitivity), DAC, Stereo DAC, Polymixer, breath controller, Inlet 1 to 5 and Outlet 1 to 5 (for Sub‑Patches), Level, Modulation Wheel, Pitch Wheel, Mix 2 to 5 (to add signals together), Damper (for sustain pedal), Constant, Sequencer (16‑step), Player (for triggering samples), Recorder (to record monophonic signals into a WAV file).
  • Sub‑Patch: these can be imported at will from the Lib folder or elsewhere.

PC Requirements

To run Tassman, according to AAS, you will need a Pentium II 233MHz or faster processor, 32Mb or more of RAM, and a PC running Windows 95 or 98. A Windows 2000 version is coming soon.


  • Huge range of acoustic and analogue sound possibilities.
  • Wonderful opportunities to create new 'acoustic' instruments.
  • Elegant front‑end Player graphics and easy‑to‑use interface.


  • High 23mS latency in current version.
  • Two stage Builder/Player design can be cumbersome.
  • Patch cords can be fiddly to use.


Tassman can create a huge range of acoustic and electronic sounds, has one of the friendliest user interfaces around for a physical modelling system, and is only marred in this first release by a high latency value during 'real‑time' performance.