A half-heigh, rack mounted synthesiser unit. The VL70m is a monophonic synthesizer whose synthesis engine uses principles of physical modeling / virtual acoustics. Developed by Stanford University, this technology describes general mathematical equations for modeling the acoustical behavior of musical instruments in much the same way that the flow of light can be modelled using ray tracing and radiosity.

In physical modeling, the vibrations of various parts of the instrument, and the interactions between them, are modeled. This provides far more realism than other synthesis meathods, including sampling and FM, as the actual vibrations of the instrument are reproduced rather than simply repeated (sampling) or approximated (FM).

The result is a virtual instrument that is highly expresive. A saxophone modelled in this way can growl, and a clarinet can squeak. It actually takes skill to get decent sound from the virtual instrument - sour notes are possible (and even frequent) and you can hear the sound of the player's breath in "airy" instruments such as a pan flute.

Another cool result is that it is possible to model the behavior of highly impratical instruments - a 100 foot long horn, or a glass saxophone, for example, and even "real" instruments can be simlated well outside of their normal pitch range.

While researches at Stanford had known how to perform this type of modeling for some time, it wasn't until the early 90's that the mathematics involved had been simplified to the point where the processing power required had been reduced enough so that they could be included in a reasonably affordable product. For example, original mathematic equations attempted to model all of the valves of a wind instrument to reproduce the way pitch changes. Researchers found that the results were comperable, but mathematically much simpler, to simply vary the length of the virtual instrument body to alter pitch.

The Stanford equations can be used to simulate a wide variety of instruments, though the core of the equations simulate a single reed instrument with a conical bore, such as a saxophone. In fact, on the VL70m, most of the sax patches sound the most realistic. The more the physical operation of an instrument differs from the single reed / concial bore model, the less accurate it sounds on the VL70m.

In physical modeling, the actual part of the instrument that is the initiator of vibration is an element. In a clarinet, this is the reed. In a trumpet, this is the player's lips. Certain types of instruments require a dual-element model in order to be simulated properly. For instance, double reed instruments such as a bassoon or oboe.

When playing a real instrument, such as a saxophone, there are a large number of "parameters" that control the sound: the pressure of the player's lips on the reed, the amount of breath pressure, the way the player is shaping his/her throat etc. All of these parameters combine to give a real instrument its expressiveness, and all of these parameters are included in the Stanford equations. It is, however,not possible to reproduce the fluidity of these parameters in real time using a standard keyboard. As a result, when playing a virtual acoustic instrument, the standard keyboard is often replaced or supplimented with either a breath controller or a wind controller. A breath controller (such as the Yamaha BC3) is a small mouthpiece that provides the instrument with breath pressure data, while a wind controller (such as the Yamaha WX5) resembles a clarinet or a soprano saxophone, complete with keys and a mouthpiece. The mouthpiece provides breath presure data and lip pressure data. Often, a wind controller is also equipped with a pitch bend wheel to provide yet more data.

The original result of this was the Yamaha VL1 physical modelling keyboard and the Yamaha VL1m rack mounted unit (both used the same synth engine). The "VL" in the names of these machines indicated "Virtual Lead" - these instruments, being able to produce only one or two sounds at a time and having a relatively high cost, were intended to be used as the "lead" instrument in a synthesiser "ensemble", where their expressiveness could stand out as the lead instrument. As an asside, it is rumored that Yamaha built a very limitted number of very expensive VP16 models. These machines could model 16 elements at a time, and thus the "VP" in their name stood for "Virtual Polyphonic".

Both the VL1 and VL1m models used a dual-element synthesis engine and thus could handle instruments such as oboes and bassoons with good accuracy. However, the VL1/VL1m was monophonic when reproducing a dual-element instrument. The VL1/VL1m could also independently play two simultaneous notes from single element instruments, and thus was duophonic. However, the VL1 and VL1m were expensive to manufacture and expensive to buy, due to the large amount of DSP processing power required to provide the dual-element model. As a result, Yamaha introduced the single-element VL70m which they could build and sell for roughly 1/3rd the price of the more sophisticated models, and in fact both the Vl1 and VL1m have been discontinued.

The VL70m is a slick little unit. As with the VL1 and VL1m before it, the front panel of the unit is encased in a dull, champagne colored metal. A large gas plasma display dominates the front of the unit, which also features an assortment of buttons to control the unit's various functions, as well as Yamaha's proprietary connectors for a Yamaha breath controller or wind controller. The wind controller connector is particularly slick, as it allows the controller to pass musical (MIDI) data to the VL70m while simultaniously providing the wind controller with power - less cables is a good thing.

The VL70m comes with two banks of 128 preset patches - each patch includes the physical model (the element and associated parameters) plus an assortment of other parameters. These parameters, including DSP effects such as reverb, and the mapping of MIDI controller data to the physical model's parameters, can all be adjusted from the front panel. When the user has adjusted the parameter's to his/her satisfaction, the resulting patch can be stored in one of 64 memory slots designed for this purpose. These memory slots simply store the parameter data and do not actually store the physical model itself, rather they point to the physical model in one of the two 128 instrument banks, or to the physical model in one of the 7 slots in the custom bank.

The custom bank is worth noting as it allows the user to store up to 7 additional physical models / elements in the unit's memory. These models can be edited using Yamaha supplied software (although those who do not own a Macintosh are forced to use some free software developed by a couple of VL70m fans who reverse engineered the data parameters) and transmitted to the unit via MIDI. Unfortunately, the limitation of 7 custom physical models is a big drawback of the VL70m as compared to the earlier Yamaha units, which allowed many more custom models to be stored. This is especially true when considering that there are many fine custom patches available for the VL70m available either commercialy or in the public domain, and it is frusterating to be able to store only 7 at a time.

Yamaha has also incorporated the VL70m's implementation of physical modeling (or similar implementations) into a host of other products, including the Yamaha EX7, Yamaha EX7R, and Yamaha EX11, as well as on an expansion card that can be plugged in to several other Yamaha synthesisers.

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