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The Audio Plug-ins

Definition of a Plug-in
    A plug-in is a software unit, generally not functioning by itself, which comes to be grafted on a more complex program and enhances the functions of this welcoming program. Initially appeared on graphic creation software like Photoshop with its filters, XPress with its Xtensions, the concept of the plug-in was then transposed in the digital audio domain, with the effects plug-ins (adding audio effects such as reverb to the MIDI/Audio sequencers and the digital audio software) and more recently with the instruments plug-ins (adding a synthesizer or a virtual sampler to its Midi/Audio program). For the user the advantages are many: creation of a modular software configuration, according to his needs, consequently reducing the cost of its configuration. On the other hand the use of these plug-ins require a powerful computer (Mac G3 or Pentium II 450 MHz minimum).
Native or DSP
    Each plug-in is composed of a whole of data-processing codes constituting a sound processing module or a synthesis sound module. These codes are written to be executed by:
  • either DSP circuits being on a special card in PCI format located inside the computer. In this case the plug-ins have a stand-alone processing, not much depending on the power of the computer processor, but on the number and power of these DSP circuits installed on the card. This gives a very reliable professional quality system but rather expensive because of the aquisition of the card. It is the case of the Digidesign Pro Tools systems, the Creamw@re Pulsar system or more recently of the TC Works PowerCore system and the UAD-1 by Mackie/Universal Audio.
  • either the intern processor of the computer: it is the solution known as "native". In this case the use of the plug-ins is related to the power of the computer. The native solution has many advantages as the the lack of DSP cards and more attractive prices, as well as a multitude of offers. But this solution involves also risks when the total working power of the computer is reached.This condition occurs in the case of an activity overload occuring at the time of a multitrack recording with the reading of other audio tracks when there is a certain number of plug-ins running. It is for that reason some plug-ins writtenin native version are "limited" to voluntarily limit the computing power necessary to the use of these plug-ins. The result is: on very greedy algorithms like reverbs , the difference in quality can be significant between a DSP version and the native version of the same plug-in.
The main formats of audio Plug-ins

    Since the emergence of the Audio and Audio/MIDI softwares, the various editors have shown their desire to each propose a personal format of plug-ins of which these are the most common :

    AudioSuite and RTAS :
    The native format of Audiosuite effects plug-ins launched by Digidesign uses an architecture of recalculation processing and uses the computing power of the computer to apply postpone effects on a sound file . This format is found in the following softwares: Audio Logic, Peak and of course Pro Tools. With the arrival of Pro Tools 5 this format evolved in real time format RTAS: Real Time AudioSuite.

    AudioUnit :
    This new format of "AudioUnit" plug-ins launched by Apple for Mac OS X, might quickly become a standard in the world of the audio on the Mac. This plug-in format, which has the advantage of being compatible with any application of the system, uses Mac OS X?s CoreAudio. For the moment only Logic Audio and in a soon to appear Digital Performer for Mac OS X handles this format.

    Direct X :
    It is the more used standard of audio plug-ins on the Windows platform and the following softwares: Cakewalk Pro Audio, Sound Forge, Wavelab, Audio Quartz Master Pro, Acid, Samplitude etc.

    MAS :
    Native format of 32 bits plug-ins created by Mark Of The Unicorn (MOTU) intended for the company softwares meaning : Digital Performer and AudioDesk. These quality plug-ins has the advantage of being able to be used in real time or postponed.

    Premiere :
    Native format of effect plug-ins created by Adobe for the virtual editing software Premiere. This format is recognized by the sequencers Digital Performer, Logic Audio, Studio Vision in recalculation and Peak in real time.

    TDM :
    Format of real time audio Plug-ins created by Digidesign for Pro Tools. It uses the DSP being on the hardware Pro Tools cards. It is a professional format of quality at a substancial price.

    VST :
    Standard of real time native Plug-ins, , multi platform (Mac and PC but warning! A PC VST plug-in does not function on Mac and vice versa) used by a very great number of audio softwares: Cubase VST, Logic Audio, Studio Vision, Sparks and SonicWORX and soon Peak. In addition the developer Amulet proposes an adapter making it possible to use on PC any VST plug-in with the applications using the Direct X format. Another developer on Mac (AudioEase) had the same idea with VST Wrapper which makes it possible to the users of DigitalPerformer to use any plug-in at the VST format.

The " effect " plug-in

    Most of the of the plug-ins used in the digital audio domain are effect plug-ins which are the "software" equivalents of effect racks. The most common effects are: reverbs, chorus, equalizers, compressors, delay etc. Two main categories of plug-ins are to be distinguished:

    Real time plug-ins
    It is the most interesting category of plug-ins for the musician since it makes it possible to listen in real time to all the modifications of the sound that occur progressively.

    Recalcultion plug-ins
    The plug-ins that do not function in real time are known as recalculation plug-ins. The principle is simple: the plug-in handles the sound of a selected audio area and creates a new file containing the processed sound . This new file comes to replace the original, which is not erased and can be used elsewhere in the piece. This type of processing makes it possible to save on the power of the host computer?s processor.

The " instrument Plug-ins " or Virtual Instruments

    Generalities

    StormRecently appeared,these softwares are the virtual equivalents of the synthetizers, the expanders and the "hardware" samplers. They can take various forms: "Tool Box" allowing to build its own modular synth, multitimbral expander, Fender Rhodes electric piano, experimental sampler etc. They can be used on a traditional computer (Mac or PC) rather than to be integrated into a whole of electronic components which constitute an "hardware" instrument. The interfacing is also virtual, since it is carried out within the software domain (OS, sequencer MIDI + Audio etc). They are controllable by MIDI, thanks to a master keyboard . They often ask a very great consumption of the computer?s processor power, and need an important RAM capacity to be used as a complement to the MIDI+ Audio sequencer.

    Use

    There are two ways of using them:

  • In "Stand alone" mode which means the synthetizer is launched like a traditional software. In this case, it is it which manages the MIDI and Audio inputs/outputs, it is independent of any other software and can be MIDI controlled in by a master keyboard. In this case you can :
    * either dedicate this instrument to a computer, and use a sequencer on another computer connected to this one by MIDI,
    * either at the same time use these virtual instruments with a MIDI + Audio sequencer as Cubase, Logic, or Digital Performer thanks to the ReWire 2.0 connection or the DirectConnect connection with Pro Tools. The ReWire 2.0 connection is a technology developed by Propellerhead Software, which makes it possible to transmit the MIDI but also the audio datas between two compatible applications. ReWire 2.0 becomes a true virtual cable being able to transport MIDI and audio datas, of a virtual synthetizer towards a MIDI+ Audio sequencer. This technology also makes it possible to synchronize these two applications. The DirectConnect connection developed by Digidesign allows the same thing with Pro Tools.

  • In "Plug-In" mode : if you use a sequencer as Cubase, Logic, Digital Performer, Pro Tools or Sonar to compose music, it is preferable to use this method. You can install virtual instruments on the mixing board of your sequencer with a simple click and you can control them by MIDI thanks to a master keyboard. There are various proprietary formats of virtual instruments in form of plug-ins: VSTi (VST instrument), DXi (DirectX instrument), MAS 2.0, and RTAS:
    * VSTi are used in Cubase, Logic (for Mac OS 9) and all compatible VST sequencers
    * DXi as for them are used in Sonar or Sonar XL, and are in the Microsoft DirectX format
    * The instruments in the format MAS 2.0 are designed for the MOTU sequencer : Digital Performer
    * The instruments in the format RTAS were created for the Digidesign?s Protools platform.

    Adjustments

    It is important to understand that to use these virtual instruments in an optimal and comfortable way, it is necessary to use a well conceived audio interface or audio card and an efficient driver (the ASIO 2.0 drivers are often well suited). Otherwise you will have have to deal with an audible latency time not suitable with a "live" use of these instruments. This means mostly a delay between what is played and what is heard that gets quickly unbearable when the instrument is played directly through a MIDI keyboard. A good adjustment can be obtained by decreasing the number of "sample per buffer" of the audio card drivers knowing that this reduction requires an additional effort of the computer?s processor. As mentionned earlier these virtual instruments often ask a very great consumption of the computer?s processor, and need an important RAM to be used in complement of MIDI+ Audio sequencer.

    The virtual instruments families

    "Sample player" synthetizers: These virtual instruments use sound samples stored on the hard drive (then in RAM to be used in real time). These are like multi purpose expanders or specialized in a particular style. Examples: SampleTank, the PlugSound series, Edirol Hypercanvas etc.

    "Modeling" synthetizers: The programmers of this kind of synthetizers try to imitate analog instruments in the most faithful possible way. They modelise for that purpose in a simplified way each electronic component (or groups of components) of the analog instrument to be imitated, then connect (always virtually) these components between them. The result is often rather successful and close to the original. The first model to appear on the market of this kind of virtual synth was Rebirth from Propellerheads (imitation of TB-303 Roland?s TB 303), followed by many others synths or vintage instruments (the products Native Instruments FM7, Pro53 or B4, Bitheadz Retro AS-1 etc).

    HalionVirtual samplers: These virtual instruments emulate the hardware samplers and you thus find on these instruments the functions of the hardware samplers. The main difference with the "sampler player" synthetizers is that the virtual samplers read about any kind of sample format (WAV, AIFF, SDII or proprietary formats) and are compatible with the various banks of sound samples which appear regularly on the market. Furthermore, they have at their disposal many processing functions on the samples (in particular filters). Examples of virtual samplers: HaLion, Kontakt, EXS24, Gigasampler etc. NB: the difference between the sample players and the samplers is less obvious in the virtual field than in the "hardware" world, insofar as one of the great differences in the hardware world between the synths/expanders and the samplers is the samples? storage capacity. Perhaps the difference which still remains relates to the processing possibilities of a sampler which are higher than those of sample player.

    Virtual Drum machines, they are either dedicated samplers to the sounds of drums and other percussion instruments, or specialized synthetizers in modeling the sounds of drums or percussions. Examples of virtual drums machines: Battery, Gamma 9000, Voodoo etc.

    Virtual studios: These are all in one software, a kind of virtual rack which contains all the devices that are found in an electronic music studio: an analog synthetizer, a sampler, a drum machine, a loop player, effects processors, a sequencer and a mixing board. Examples of virtual studios: Reason, Studio 9000, Storm etc.


    If you want to discover more informations and read all my articles (especially about midi) please come on my home page at: http://perso.club-internet.fr/clborne
    Translated from french by Dominique ZBIEGIEL, aka DOMZ

About the author: Claude Borne
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