Plugin formats : VST , AU , AAX , RTAS , TDM.

What is AAX and AU? What difference do they have with VSTs? In this article we will discuss the different plugins formats and their characteristics.

VST ( Virtual Studio Technology ) – Steinberg

This format, created in 1996 by Steinberg, is one of the most used type of plugins in the world of music production. These plugins usually work through the DAWs (Digital Audio Workstation), but recently more standalone plugins are used, which do not require any external interface. Most VST plugins are virtual instruments (VSTi), effects (VSTfx) or MIDI effects (such as arpegiators, transpose, etc.).

The VST format became famous for its versatility with MIDI controls and the possibility of mixing instruments and chain effects (chaining), in the style of analog racks. Steinberg’s commitment to converting the VST into a standard helped third-party companies to create new VSTs with freedom, most of them created for Windows – since OS X comes with its own AU (Audio Unit) architecture . The latest version of this format, VST 3.6.7, came out in March 2017. It includes the previous version of VST3 for Linux and development kits “Propietary Steinberg VST3” and “Open-Source GPLv3”. Some of the DAWs that accept VSTs :

  • Ableton Live
  • Audacity
  • FL Studio
  • Logic Pro
  • Reason
  • Steinberg Cubase

AU ( Audio Unit ) – Apple

Audio Units (AU) is the format created by Apple Inc. for the macOS and iOS. AUs are a set of application programming interface (API) services provided by the operating system to generate, process, receive or edit audio transmissions in  real time with minimal latency. The AU format allows you to stretch the audio time of the file and the pitch scale, the conversion of the sample rate and the transmission through a local area network. It also comes with a set of AU add-ons like equalizer filters, dynamic processors, delay, reverb and an instrument – the Soundbank synthesizer.

This format is compatible with macOS and iOS and the programs you can use on them:

  • GarageBand
  • Logic Pro , X y Express
  • Final Cut Pro
  • Ableton Live
  • Studio One

RTAS ( Real Time AudioSuite ) – Avid Technology

Real-Time AudioSuite (RTAS) is an audio plug-in format developed by Digidesign, currently Avid Technology for its Pro Tools LE and Pro Tools M-Powered systems, although they can run on Pro Tools HD and Pro Tools TDM systems. The architecture of this format is designed to work in real time, mimicking the form of hardware in the traditional mixer.

RTAS add-ons use the processing power of the computer instead of the DSP cards used in Pro Tools HD systems and the TDM format. On April 7, 2013, Avid announced Pro Tools 11. As of this release, Avid has made of the AAX plugin the only format compatible with Pro Tools. At launch, many third-party add-on developers have not yet adapted their software to the new AAX format, so Avid will sell Pro Tools 11 with a license 11 and 10, which will allow users to run Pro Tools 10.3.8, which is the latest version that RTAS will support.

TDM (Time-division Multiplexing) – Avid Technology

TDM is a format for Pro Tools plugins that are installed on external hardware, such as dedicated DSP processors for ultra high precision and quality. TDM plugins are usually installed in large, high-quality studios equipped with dedicated processors, instead of having all the processing done by the computer’s CPU.

The TDMs are specifically designed to take advantage of the features and resources of Pro Tools HD systems. HD systems combine the high-end and full-featured version of Pro Tools software with specialized external hardware in the form of DSP cards. One of the main drawbacks of TDM plug-ins is their price. In addition to the cost of the plugins, you will also have to invest in a suitable system equipped with DSP. Traditionally, recording engineers and music producers were advised to go to TDM only if they could afford it. Otherwise, the RTAS plugins offered a more than viable alternative.

AAX (Avid Audio eXtension) – Avid Technology


AAX is a unified format, in which Avid wants to unite the characteristics of TDM and RTAS, which comes in 2 variations: AAX DSP, AAX Native. This format was introduced when Avid created a 64-bit version of Pro Tools, which meant that a format with 64-bit processing was necessary. With AAX, you can share sessions between Pro Tools systems accelerated by DSP and native Pro Tools systems and continue using the same plugins. The AAX is great investment in the future of music plugins, which will make the TDA and RTAS systems obsolete in the not so distant future.