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Audio Software Plug-in Roundup, Part 1: Background

Exploration By Paul White
Published June 1999

Digidesign's Pro Tools system, with its dedicated DSP hardware, pioneered the concept of audio plug‑ins on the Mac — first for off‑line processing and later for real‑time use.Digidesign's Pro Tools system, with its dedicated DSP hardware, pioneered the concept of audio plug‑ins on the Mac — first for off‑line processing and later for real‑time use.

The plug‑in compatibility of most audio software means that you can add new effects and processing capabilities — but not all programs support the same types of plug‑in, and some require additional hardware. In the first part of a comprehensive roundup, Paul White and Martin Walker look at the different plug‑in formats available.

Audio software plug‑ins can offer anything from effects and dynamics processing to pitch correction and guitar amp simulation, but there are several different plug‑in types. Some of these can be used within various types of host software, while others are dedicated to a single package or tied to a single hardware platform. The more powerful ones require additional DSP cards to run, while others need nothing more than a reasonably powerful host computer. In the forthcoming instalments of this series, we'll be conducting a detailed roundup of all the plug‑ins that are currently available. Before we look at individual plug‑ins, however, we'll provide an overview of the different types so that you know which ones are relevant to your own system. Since audio plug‑ins began on the Mac, we'll cover the various Macintosh formats before looking at the PC situation.

The Digidesign Innovation

Steinberg's Wavelab was one of the first applications to support plug‑ins on the PC: shown are the Loudness Maximizer and 'Grungelizer'(!).Steinberg's Wavelab was one of the first applications to support plug‑ins on the PC: shown are the Loudness Maximizer and 'Grungelizer'(!).

Audio software plug‑ins first came about in the early days of Digidesign, when Sound Designer II and Pro Tools II were the leading‑edge sound‑editing and multitrack recording packages for Macintosh computers. Digidesign were the company who got the ball rolling as far as third‑party plug‑in support was concernedand before long companies such as Waves were designing their plug‑ins to run on the system. Pro Tools II hardware (and the earlier Sound Tools card) included an area of DSP that could be used to run software plug‑ins, so when Sound Designer II was run on this hardware, it too could make use of the plug‑in functions.

These early plug‑ins could be used either to destructively edit an audio file or, alternatively, a single plug‑in could be used in real time to give a processed output without changing the original file. Setting up the plug‑in was done while auditioning a short looped section of the audio file held in RAM memory. Then, when the best settings were found, the file could either be 'Processed' (destructive) or the plug‑in used in 'Playback' mode (non‑destructive). To use multiple plug‑ins, it was necessary to destructively edit the file using the first plug‑in, then work on the edited file using the second plug‑in, and so on.

The next evolutionary step for Digidesign was the introduction of Pro Tools TDM (which stands for Time Division Multiplexing) hardware, which incorporates both DSP chips to run plug‑ins and a complex bussing system for virtual mixing and plug‑in patching. This requires a proprietary format TDM plug‑in designed to work exclusively with TDM versions of Pro Tools II or Pro Tools III hardware (and now the neMix/24 system, though that requires a different version of the plug‑in). TDM is widely used today, mainly by professionals, and the sophisticated routing made possible by the Pro Tools III hardware TDM buss means that as many plug‑ins may be run simultaneously as the available hardware DSP will allow. Owners can add more DSP cards to accommodate more plug‑ins. Furthermore, unlike earlier plug‑ins, TDM plug‑ins may be patched into various parts of the signal path (channel inserts, aux sends and so on) via Pro Tools's virtual mixer. Most TDM plug‑ins may also be automated via the Pro Tools software, though it should be noted that TDM plug‑ins are not accessible from within Sound Designer II, even if it is running on Pro Tools hardware. SDII (which is effectively now at the end of its life, as it will not be developed further) has its own plug‑in format.

Unlike pre‑TDM plug ins, TDM effects and processors operate only in non‑destructive mode, so to create a permanently changed sound file, it is necessary to record the processed results to a fresh track or to use one the alternative non‑real‑time plug‑ins that works with Pro Tools hardware. Note that the Sound Designer II stereo editing software can still run on TDM Pro Tools hardware, but only the earlier Macintosh Nubus systems support the use of SDII plug‑ins. TDM plug‑ins are available from a large number of third‑party companies including Arboretum, Drawmer, Focusrite, Lexicon, Line 6, Opcode, TC Electronic (under the name TC Works), Waves and so on.

Because TDM plug‑ins use DSP chips located on 'Farm Cards' that are an integral part of Pro Tools TDsystems, they require little native (ie. host computer‑based) processing power. Though Pro Tools hardware is costly, it does mean that you're not constantly having to buy a faster computer to handle more plug‑ins, and equally importantly, you don't suffer the monitoring latency of systems running host processor‑based plug‑ins that rely on the computer's own processor to do all the work.

Non‑real‑time effects may be run on a Pro Tools system via the AudioSuite plug‑in system, another proprietary Digidesign format that is similar in operation to Adobe's Premiere plug‑in format (see below). Audiosuite plug‑ins work much like pre‑TDM plug‑ins insomuch as the plug‑in is first adjusted to give the desired result, then the audio file is processed off‑line. Some TDM plug‑ins provide the option to have both TDM and Audiosuite functionality from the same plug‑in, though this is by no means universal.

There is a temptation to think that a powerful computer will run almost a limitless number of audio channels, mixer channels, virtual synths and effects, but the reality is that this is still asking a lot of any machine.

Perhaps Digidesign's most astute move was to open up its hardware platform to third‑party sequencer companies, allowing high‑quality audio recording and editing to be integrated with MIDI from within a familiar sequencer interface. Today, virtually all serious Mac‑based sequencers can work with Pro Tools TDM hardware, including Opcode's Studio Vision, MOTU's Digital Performer, Steinberg's Cubase, Emagic's Logic Platinum and so on.

Until recently, Digidesign systems were designed only for use on Macintosh computers, but their new Mix/24 system can work both on Macs and on PCs running Windows NT. Mix/24 doesn't need a separate DSP Farm card (though it is still expandable) and it is significantly more powerful than Pro Tools III. A different design of TDM plug‑in is required to run on Mix/24 — older TDM plug‑ins won't work — though it is possible to use Pro Tools III DSP Farm cards in a Mix/24 system in order to use older plug‑ins within the new environment. Future versions of TDM plug‑ins will probably contain code to allow them to run on both Pro Tools III and Mix/24 hardware.

Adobe Premiere

Audio Software Plug-in Roundup, Part 1: Background

Premiere is a non‑real‑time plug‑in format developed by software giant Adobe and implemented in several applications, both in the music field and in the area of multimedia presentation software, such as Adobe Premiere. It requires no additional hardware, and is supported by Opcode's Studio Vision, MOTU's Digital Performer, Emagic's Logic Audio and BIAS's Peak, but not by Steinberg's Cubase VST.


Audio Software Plug-in Roundup, Part 1: Background

Steinberg are worthy of a special mention in this article because, like Digidesign, they have done a lot to introduce standards and establish cross‑platform compatibility in the world of computer audio recording. However, their first venture into plug‑ins was to design TDM plug‑ins, specifically Spectralizer, DeClicker, TuneA, TimeGuard, RedValve‑It (guitar amp emulator) and Magneto (tape saturation emulator). Next came the Wavelab stereo editor, which was initially supported by a dedicated range of plug‑ins marketed bSteinberg. These are the DeNoiser, DeClicker, Spectralizer, Loudness Maximizer, FreeFilter and Magneto. Wavelab also supports DirectX PC plug‑ins (see page 174 for more details), which can be run at the same time as the dedicated Wavelab plug‑ins. All Wavelab plug‑ins use the power of the host DSP to run, and no additional hardware. Both real‑time and non‑real‑time (destructive) operation is available.

Steinberg originally devised the VST plug‑in format to work with Cubase VST for the Macintosh (first VST PC, then DirectX plug‑ins were used for the PC version), but Steinberg have now opened the VST format up to other manufacturers so that Opcode, Emagic and MOTU audio sequencers can use exactly the same plug‑ins. VST plug‑ins also use the host computer's processor to do all the work, and consequently, the number of effects that can be run simultaneously is limited by the available computing power. The faster the machine, the more plug‑ins can be run together, and of course computers get faster every year.

Plug‑ins got off to a slower start on the PC platform, largely because the Mac was already well established for musicians.

Such host‑based systems tend to suffer from latency when monitoring recordings with effects because of the finite time it takes for the computer to route and process the audio. In some systems, the delay is so pronounced that it can make keeping time very difficult for the musician. Again, Steinberg have streamlined things here by introducing the ASIO audio driver, which keeps latency to a minimum. ASIO drivers are available for both Macs and PCs, and allow newly recorded signals to be monitored with their native effects. ASIO II, which has recently been announced, further reduces monitoring latency with compatible hardware, but at the expense of being able to hear the effects while recording. As with the VST plug‑in format, Steinberg have made the ASIO protocol available to other manufacturers so that it may be adopted as an industry standard.


Audio Software Plug-in Roundup, Part 1: Background

Another recent development comes from MOTU, whose MAS (MOTU Audio System) enables you to record digital audio on your Mac using no additional hardware. Used in conjunction with their Digital Performer v2.5 software, MAS is a system extension that uses the host processor to provide a selection of 32‑bit real‑time plug‑ins. MAS also directly supports a variety of hardware cards. Among these are the MOTU 2408 (as you might expect), along with Digidesign's Audiomedia II/III, the Sonorus STUDI/O, any PCI‑based Pro Tools system via Direct I/O, the Yamaha DSP Factory, Event Layla and the Korg 1212. For non‑TDM systems, you now get real‑time effects with your Digidesign hardware, while with a Pro Tools TDM system and a fast Power Mac, MAS may manage more real‑time processing than you are currently getting under TDM — you can freely switch between MAS and the Digidesign Audio Engine (DAE). A variety of plug‑ins are included, but other third‑party developers such as Waves, DUY, Antares, and Arboretum are also creating
MAS plug‑ins.

The PC Platform

MOTU's Digital Performer MIDI + Audio sequencer now supports VST plug‑ins, but also offers its own MAS plug‑in format, as used by the supplied Parametric EQ and eVerb reverb.MOTU's Digital Performer MIDI + Audio sequencer now supports VST plug‑ins, but also offers its own MAS plug‑in format, as used by the supplied Parametric EQ and eVerb reverb.

Plug‑ins got off to a slower start on the PC platform, largely because the Mac was already well established for musicians. Initially, the only effects available were those supplied with the early WAV file editors, and these were only available as off‑line processes — real‑time processing was beyond the capabilities of the Intel 486 processors in use at the time. Most were bundled with soundcards, and were little more than fun gimmicks, providing basic delay‑based effects such as flanging, chorus, slapback, and echo. One of the first to offer better quality was the excellent (for its time) Wave For Windows editor from Turtle Beach Systems, but two applications in particular really starting the ball rolling for quality effects on the PC: Sonic Foundry's Sound Forge and Steinberg's Wavelab. Both of these editors shipped with a wide variety of high‑quality off‑line effects, which were good enough to use in commercial tracks.

The turning point for real‑time audio, by contrast, came not from a specialist audio software company but from Microsoft. ActiveMovie was originally designed by Microsoft as a media‑streaming architecture for Windows, and was intended to replace Video for Windows. Rather than having to wait for a complete audio or animated graphics file to be processed before it could be auditioned, 'streaming' was designed to work in real time, by processing a stream of smaller packets of data, each of which could be heard or seen before the next arrived. This also allowed synchronisation between video and audio to be maintained, as long as the user's system was fast enough. However, since it had a standard set of underlying interfaces for both audio and video, it proved an ideal way to create plug‑in applications that would work with any host program that supported ActiveMovie.

Version 4.0a of Sound Forge was the first PC application to use this new technology to provide real‑time previews of its audio effects, but the ActiveMovie streaming standard also allowed third‑party plug‑ins to be used with it.

Wavelab version 1.6 followed shortly afterwards with similar facilities, and Cakewalk Pro Audio version 6 was the first MIDI + Audio sequencer to be upgraded in the same way. Once third‑party plug‑in developers realised that they had potential customers among owners of Sound Forge, Wavelab, Cakewalk and the forthcoming Cubase VST as well, the PC was firmly on the map for real‑time audio.


Sonic Foundry's Sound Forge (version 4.0a) was the first PC audio editing package to make use of Microsoft's ActiveMovie standard in its plug‑in provision.Sonic Foundry's Sound Forge (version 4.0a) was the first PC audio editing package to make use of Microsoft's ActiveMovie standard in its plug‑in provision.

Confusingly, Microsoft have changed the name of their streaming technology on various occasions. From the original ActiveMovie, it was renamed DirectX Media Streaming Services (DMSS), and many people still refer to it as DirectX. However, strictly speaking DirectX is a whole suite of components designed toptimise the performance of various multimedia elements such as full‑colour graphics, video, 3D animation, and surround sound. The DirectX Foundation layer ensures that any multimedia application will run on any PC with Windows 95/98 (or NT 5.0), whatever hardware it uses. It does this by providing a set of APIs (Application Programming Interfaces) that sit between hardware and software, providing a standard way for software developers to access any piece of hardware. Above the Foundation layer is the DirectX Media layer, and it is here that the streaming components sit, including DirectShow. This provides streaming playback of a variety of formats, including Quicktime, AVI, MPEG, and WAV. For audio purposes it is the WAV support that interests us. Effectively, any PC plug‑in or application that refers to DirectShow, DirectX, DMSS, or ActiveMovie is using the same Microsoft technology.

Cubase VST

Creamware's SCOPE platform, as used in the Pulsar card, provides powerful on‑card DSP which can be used both by effects and processing plug‑ins, and by software synths, samplers and mixers.Creamware's SCOPE platform, as used in the Pulsar card, provides powerful on‑card DSP which can be used both by effects and processing plug‑ins, and by software synths, samplers and mixers.

Steinberg initially released Cubase VST on the Mac platform, and it was the first application to feature their new ASIO (Audio Streaming Input Output) streaming technology, which worked in a similar way to DirectShow. When VST arrived for the PC the same ASIO real‑time streaming was built in, but DirectShow provided such competition that Steinberg modified the PC version of Cubase VST to run these plug‑ins as well. However, various developers still provide VST‑specific versions of their plug‑ins, even to the extent that both VST and DirectShow versions may be supplied on a single CD‑ROM. There are several reasons for this. One advantage of using a VST plug‑in over its DirectShow version is that it normally runs with a slightly lower processor overhead, largely because VST‑specific plug‑in code is more tightly integrated with the rest of the VST application. More important for many people is that the controls of VST plug‑ins can be automated — any plug‑in control movement can be recorded in the Audio Mix track. Many modern effects such as filter sweeps benefit from automation, since they ideally need to be sync'ed to the music. This is the reason that Waldorf only released their D‑Pole plug‑in in VST format. Closely related to VST plug‑ins are those provided with Wavelab, and since both products are developed by Steinberg they are mutually compatible — if you have Wavelab, then any Wavelab‑specific plug‑ins will appear as options inside VST, and vice versa.


Several advanced DSP‑based soundcards have been released recently, of which one of the most exciting is Creamware's Pulsar (reviewed March '99). Pulsar is the first product to use the SCOPE (Scalable Open Processing Environment) platform, with more powerful cards set to follow. Creamware use the fast SHARC DSP chips, and a large selection of plug‑in effects are provided as part of the package, along with many types of plug‑in synthesizer, such as analogue and FM. However, third‑party developers are being encouraged to create versions of their plug‑ins to run on the SCOPE platform, and the first of these are just starting to be released. SCOPE plug‑in code is uploaded to the DSP chips on the soundcard, and then runs entirely within these DSP chips. There is no drain on the main PC processor, although you do need a lot of RAM in your PC to keep the system running smoothly. Mac drivers for the Pulsar are expected shortly, and Creamware are hoping that SCOPE will become a cross‑platform system to rival that of Digidesign.


Another PC platform that hosts real‑time (as well as off‑line) plug‑ins is the Soundscape SSHDR system, and the same plug‑ins can also be used with the company's recently released Mixtreme soundcard (reviewed in SOS April '99 issue). This is similar in concept to SCOPE, expect that it uses Motorola DSP chips, and has a slight bias towards audio mixing and effect plug‑ins, rather than the multiple synthesis options provided with the Pulsar card. Soundscape have a small range of their own plug‑ins, and third‑party developers are also supporting the platform, including TC Works, Aphex, and Wave Mechanics. Although, like most hardware‑specific plug‑ins, these are significantly more expensive than DirectShoones, the audio quality is correspondingly high. No dynamic automation is available, but you can take a snapshot at any time that saves the current position of every control in the mixer, including the plug‑ins.


Your choice of plug‑ins largely depends on the hardware you have, but native and DSP‑based effects can usually be freely mixed. Note, however, that you can't run VST or similar plug‑ins on hardware that uses its own DSP for effects processing. For example, if you use a Mac‑based Pro Tools system, any VST effects must be run within the Mac and routed out via the Mac's AV output or supported soundcard. The TDM effects run on the Pro Tools hardware and are routed via the Digidesign interface. It's almost like having two types of mixer channel in your computer, each with access to different effects plug‑ins and routable to different physical outputs.

Though host processor‑based plug‑ins are the cheap option, keep in mind that there are latency penalties unless you're prepared to monitor without effects. Even if your card doesn't handle 'straight through' monitoring, you can rig up a system to monitor the signal being recorded via your mixer rather than the soundcard output, but you won't hear the effects until you play back the track. Properly designed hardware‑based platforms have negligible latency and allow you to monitor effects as you record.

There is a temptation to think that a powerful computer will run almost a limitless number of audio channels, mixer channels, virtual synths and effects, but the reality is that this is still asking a lot of any machine. If you intend to base your studio entirely around the computer, your best bet is to get the most powerful machine you can afford, give it lots of memory and separate fast hard drives for audio, then run it at no more than half to two‑thirds of its maximum capacity. The amount of processing power taken by individual functions is always fluctuating, and if you run too close to the edge, you'll find that on occasions, your software will write cheques that your computer can't cash (or should that be cache?)!

Thanks to Martin Gadgil (SCV London), Thomas Went (Steinberg) and Ralf Schlunzen (TC Electronic) for their help in compiling this article.

Never Mind The Quality — Feel The (Bit) Depth

The time has long gone when you could judge plug‑in audio quality solely by how many bits are employed for the calculations. Nearly all modern plug‑ins can treat either 16‑ or 24‑bit audio streams, but even when treating 16‑bit audio, calculations are likely to be carried out internally with a resolution of 24, 32 or even 64 bits. Although the theoretical dynamic range of the individual internal calculations may therefore be huge (anything up to several hundred dBs!), the final results will be determined by the accumulated rounding errors of the many thousands of calculations, which will greatly depend on the quality of the algorithm used.

It is also important to understand that the design aims may be different across multiple formats. Since some plug‑ins (such as DirectShow and VST) rely on the power of the host processor, it is important that this drain is kept as small as possible so that other plug‑ins and applications can be run simultaneously. However, such restrictions may not be so important when running DSP‑based plug‑ins, since considerably more processing power can be devoted to a single plug‑in. For instance, TC Works market both DirectShow and Soundscape plug‑ins using their considerable expertise of reverb algorithms. The TC Native Reverb has been carefully optimised to minimise processor overhead, since reverbs are particularly processor‑intensive, and the result is a good‑sounding reverb with modest processor requirements. In contrast, the TC Reverb marketed for Soundscape and Mixtreme uses several times more processing power, but this has absolutely no effect on the main processor, since the DSP chips are doing all the work. The DSP version is considerably more expensive, but the sound quality is also considerably better. As always, you should use your ears to judge the difference. There's a lot to be said for using cards that include hardware‑powered reverb as this frees up your computer's processor for other tasks.