Effect Menu



Audacity includes many built-in effects and also lets you use a wide range of plug-in effects. You can download many free plug-ins for Audacity from http://audacity.sourceforge.net/download/plugins and the links thereon. To apply an effect, select part or all of the tracks you want to modify, and select the effect from the menu. Titles which end in an ellipsis (...) will bring up a dialog asking you for more parameters.

Although by default, the only effects shortcut is to repeat the last used effect, it is possible to set up your own shortcut for any effect in the menu. For instructions on how to do this please see Keyboard Preferences.

Classes of Effect
There are five classes of effect - the built-in Effects, and four classes of plug-in effects which allow you to download and install additional effects. All classes of effect are applied in the same way. The effects classes are:


 * Built-in Effects
 * Nyquist Effect Plug-ins
 * LADSPA Effect Plug-ins
 * VST Effect Plug-ins (Windows and Mac only)
 * Audio Unit Plug-ins (Mac only)

Where a Built-in or shipped Nyquist effect has settings, its description page (accessed by the links below) shows an image of the interface and its default settings.

List of Built-in Effects
Audacity's built-in effects (those that appear in the program irrespective of the contents of your Audacity and other Plug-ins folders) are above the divider in the Effect menu. Most of the built-in effects have a "Preview" button. This allows you to listen to how the first three seconds of the selected audio will sound with your effect applied. If it does not sound quite as you want, adjust the controls of the effect and preview again. The preview length can be changed on the Playback tab of Preferences.

Amplify...
Increases or decreases the volume of the audio you have selected. When you open the dialog, Audacity automatically calculates the maximum amount you could amplify the selected audio without causing clipping (distortion caused by trying to make the audio too loud).

Auto Duck...
Reduces (ducks) the volume of one or more tracks whenever the volume of a specified "control" track reaches a particular level. Typically used to make a music track softer whenever speech in a commentary track is heard.

Bass and Treble...
Increases or decreases the lower frequencies and higher frequencies of your audio independently. It behaves just like the bass and treble controls on a domestic stereo system.

Change Pitch...
Change the pitch of a track without changing its tempo.

Change Speed...
Change the speed of a track, also changing its pitch.

Change Tempo...
Change the tempo of a selection without changing its pitch.

Classic Filters...
Provides three different types of filters which together emulate the vast majority of analog filters, and provides useful tools for analysis and measurement.

Click Removal...
Click Removal is designed to remove clicks on audio tracks and is especially suited to declicking recordings made from vinyl records. It will usually work best on very short clicks. For broader individual pops in selections up to 128 samples wide (about three milliseconds at 44100 Hz project rate), you could try the Repair effect.

Compressor...
Compresses the dynamic range by two alternative methods. The default "RMS" method makes the louder parts softer, but leaves the quieter audio alone. The alternative "peaks" method makes the entire audio louder, but amplifies the louder parts less than the quieter parts. Make-up gain can be applied to either method, making the result as loud as possible without clipping, but not changing the dynamic range further.

Echo...
Repeats the selected audio again and again, normally softer each time. The delay time between each repeat is fixed, with no pause in between each repeat. For a more configurable echo effect with a variable delay time and pitch-changed echoes, see Delay...

Equalization...
Adjusts the volume levels of particular frequencies.

Fade In
Applies a fade-in to the selected audio, so that the amplitude changes gradually from silence at the start of the selection to the original amplitude at the end of the selection. The shape of the fade is linear. The rapidity of the fade-in depends entirely on the length of the selection it is applied to.

Fade Out
Applies a fade-out to the selected audio, so that the amplitude changes gradually from the original amplitude at the start of the selection down to silence at the end of the selection. The shape of the fade is linear. The rapidity of the fade-out depends entirely on the length of the selection it is applied to.

Invert
Flips the audio samples upside-down. This normally does not affect the sound of the audio at all. It is occasionally useful for vocal removal.

Leveler...
Leveler is a simple, combined compressor and limiter effect for reducing the dynamic range of audio. It reduces the difference between loud and soft, making the audio easier to hear in noisy environments or on small loudspeakers. It is best suited to speech recordings but at heavier settings or used multiple times it can also be used as a simple distortion effect for voices or instruments.

Noise Removal...
Removes constant background noise such as fans, tape noise, or hums. It will not work very well for removing talking or music in the background. More details here.

Normalize...
Use the Normalize effect to set the maximum amplitude of a track, equalize the amplitudes of the left and right channels of a stereo track and optionally remove any DC Offset from the track.

Nyquist Prompt...
Launches a dialog where you can enter Nyquist commands. Nyquist is a programming language for producing and processing audio. For more information see Nyquist Plug-ins Reference.

Paulstretch...
Use Paulstretch only for an extreme time-stretch or "stasis" effect. This may be useful for synthesizer pad sounds, identifying performance glitches or just creating interesting aural textures. Use Change Tempo or Sliding Time Scale rather than Paulstretch for tasks like slowing down a song to a "practice" tempo.

Phaser...
The name "Phaser" comes from "Phase Shifter", because it works by combining phase-shifted signals with the original signal. The movement of the phase-shifted signals is controlled using a Low Frequency Oscillator (LFO).

Repair
Fix one particular short click, pop or other glitch no more than 128 samples long.

Repeat...
Repeats the selection the specified number of times.

Reverb...
Adds ambience or a "hall effect".

Reverse
Reverses the selected audio, so that it will sound as if it is playing from the end to the start.

Sliding Time Scale / Pitch Shift...
Allows you to make a continuous change to the tempo and/or pitch of a selection by choosing initial and/or final change values.

Time Tracks can be used to bend tempo more flexibly (also affecting pitch) using Envelope Tool.

Truncate Silence...
Automatically try to find and eliminate audible silences. Don't use with faded audio.

Wahwah...
Rapid tone quality variations, like that guitar sound so popular in the 1970's.

Wahwah uses a moving bandpass filter to create its sound. A low frequency oscillator (LFO) is used to control the movement of the filter throughout the frequency spectrum.

The phase of the left and right channels is automatically adjusted when given a stereo track, so that the effect seems to travel across the speakers.

The following four classes of effect always appear underneath the divider in the Effect menu. Released builds of Audacity include sample Nyquist and/or LADSPA effects.



Nyquist Effects
ToDo Not a priority for 2.0, but needs a little more here: Nyquist plug-ins provide most of the optional effects underneath the divider in the Effect menu. They are also used to provide some of Audacity's built-in audio generators and analysis tools. A wide range of additional Nyquist effect, generation and analysis plug-ins can be obtained from Download Nyquist Plug-ins on our Wiki.
 * where to get docs
 * the debug button in Nyquist effects
 * Nyquist workbench
 * Steve 25Apr12: Does "Nyquist Workbench" fit on this page? When installed it is listed in the menu.
 * Gale 10Jul13: It should probably be mentioned here with a link to http://wiki.audacityteam.org/wiki/Nyquist_Plug-ins_Reference#Nyquist_Workbench . People won't see Workbench in any menu until they act on that Wiki page.
 * Peter 22Aug13: added section for Nyquist Workbench - and a link there to the Wiki article.


 * To add a Nyquist plug-in, put it in the Audacity "Plug-ins" folder.
 * On Windows and OS X the "Plug-ins" folder is in the directory where Audacity resides - usually C:\Program Files on Windows or the "Applications" folder on OS X.
 * On Linux, the "plug-ins" folder is in usr/share/audacity if you installed an Audacity package supplied by your distribution, or usr/local/share/audacity if you compiled Audacity from source code. Optionally a plug-in folder can be created in the home directory ~/.audacity-files/plug-ins.
 * The next time you launch Audacity, plug-ins you added will appear in the Effect, Generate or Analyze menus as appropriate.

Nyquist Workbench
The Nyquist Workbench gives the ability to run arbitrary Nyquist code in Audacity from a graphical IDE (Integrated Development Environment). See Nyquist Workbench in the Wiki.

Nyquist plug-ins included in Audacity
The following sample Nyquist plug-ins are included in released builds of Audacity:

Adjustable Fade...
Launches a dialog box where you can choose the shape of the fade in or fade out to be applied. You can also create fades to and from other than silence or full volume. An example of this might be a fade in from 20% of the original volume to 80% of the original volume.



Clip Fix...
Attempts to reconstruct clipped regions by interpolating the lost signal.

Cross Fade In
Applies a curve that will result in equal volume throughout the fade once the faded in and faded out regions are mixed.

Cross Fade Out
Applies a curve that will result in equal volume throughout the fade once the faded in and faded out regions are mixed.

Delay...
A configurable delay effect with variable delay time and pitch shifting of the delays.

High Pass Filter...
Passes frequencies above its cut-off frequency and attenuates frequencies below its cut-off frequency; this can be used to reduce low frequency noise.



Low Pass Filter...
Passes frequencies below its cut-off frequency and attenuates frequencies above its cut-off frequency; this can be used to reduce high pitched noise.

Notch Filter...
Greatly attenuate ("notch out") a narrow frequency band. This is a good way to remove mains hum or a whistle confined to a specific frequency with minimal damage to the remainder of the audio.



Studio Fade Out
Produces a smooth and musical sounding fade out, by applying a sinusoidal fade with a progressive low pass filter from full spectrum at the start of the selection to 100 Hz at the end.

Tremolo...
Modulates the volume of the selection at the depth and rate selected in the dialog. The same as the tremolo effect familiar to guitar and keyboard players.

Vocal Remover (for center-panned vocals)...
Attempts to remove center-panned audio from a stereo track; vocals are often (but not always) recorded in this way. Vocals (or other audio) can only be removed with this plug-in when panned to center, in other words sounding equally loud in both left and right channels. Help text is available from within the effect's dialog box.

Vocoder...
Vocoder synthesizes a modulator (usually a voice) in the left channel of a stereo track with a carrier wave in the right channel to produce a modified version of the left channel. Vocoding a normal voice with white noise as provided in the effect will produce a robot-like voice for special effects. Other carriers can be used for subtly different voices. Vocoder can only be applied to unsplit stereo tracks.

LADSPA Effects
LADSPA (Linux Audio Developer's Simple Plugin API) plug-ins were originally developed for the Linux platform, but ports of some plug-ins are available for Windows and OS X as well. Most LADSPA plug-ins are effects, but they are also used to provide some of Audacity's built-in audio generators and can be used for audio analysis. Additional LADSPA plug-ins can be downloaded for Windows, Mac and Linux.


 * To add a LADSPA plug-in, put it in the Audacity "Plug-ins" folder.
 * On Windows and OS X the "Plug-ins" folder is in the directory where Audacity resides - usually C:\Program Files on Windows or the "Applications" folder on OS X.
 * On Linux, the "plug-ins" folder is in usr/share/audacity if you installed an Audacity package supplied by your distribution, or usr/local/share/audacity if you compiled Audacity from source code.
 * The next time you launch Audacity, plug-ins you added will appear in the Effect, Generate or Analyze menus as appropriate.

Three sample LADSPA effects are included with Windows and Mac builds of Audacity:



Hard Limiter...
An extreme compressor effect. It can sometimes be used to remove stubborn clicks.

SC4...
A stereo compressor with a variable envelope follower for RMS / peak behaviour.

Audacity will also load LADSPA plug-ins from the following system locations:
 * All operating systems: The path specified by the LADSPA_PATH environment variable
 * additionally on OS X:
 * ~/Library/Audio/Plug-Ins/LADSPA
 * /Library/Audio/Plug-Ins/LADSPA
 * additionally on Linux/Unix:
 * $INSTALL_PREFIX/ladspa
 * /usr/local/lib/ladspa
 * $LIBDIR/ladspa

Install VST Effects dialog
When you use Audacity for the first time it will scan on Windows and Mac OS X for VST effects in the Audacity "Plug-Ins" or "Plugins" folder and in other specific locations. The following "Install VST Effects" dialog will appear where you can choose which VST effects to load into the Audacity Effect Menu.
 * Installvst.png

The names of the detected plug-ins will be listed alphabetically for each folder in the Path column. All list items have their checkboxes checked by default, the green checkmark indicating that the plug-in will be loaded. To load all the detected plug-ins, just click then Audacity itself will launch.

To disable loading of a plug-in, left-click the item's row or checkbox which removes the checkmark. Similarly, click to re-enable a disabled item. Using the keyboard, press arrow,  arrow,  or  to navigate the list then press  to check or uncheck the current item's checkbox. Finally, click to load the enabled plug-ins and launch Audacity. Providing you click and the enabled plug-ins load successfully, then next time you launch Audacity there will be no VST effects dialog. The plug-ins that you previously enabled in the dialog will appear in the Effect menu, ready to be used when you select them.

If you click in the dialog or if loading a faulty plug-in causes Audacity to crash,  the "Install VST effects" dialog will appear again next time you launch Audacity. If Audacity crashed you can therefore use the dialog to experiment by disabling plug-ins that may have crashed. Alternatively, before restarting Audacity you can look in the plugins.cfg file in the Audacity folder for application data. This file will list which plug-ins Audacity had managed to load before it crashed.

Once loaded, the installed VST effects will appear underneath the divider in the Effect Menu. Some of the VST's will be listed as VST:. Other VST's will be listed under the name of the plug-in vendor. 

Adding a new VST effect in Audacity
To add a new VST effect, put its DLL or VST file plus any configuration files or folders it requires in the Audacity "Plug-ins" or "Plugins" folder which is in the directory where Audacity resides. You can also create a folder called "VST" in the Audacity installation directory and add VST plug-ins there.

Alternatively, VST plug-ins can be placed in one of the following system locations: Then:
 * Windows:
 * Windows Registry key HKCU\Software\VST\VSTPluginsPath
 * Windows Registry key HKLM\Software\VST\VSTPluginsPath
 * The path specified by the "VST_PATH" environment variable
 * Mac OS X:
 * ~/Library/Audio/Plug-Ins/VST
 * /Library/Audio/Plug-Ins/VST
 * The path specified by the "VST_PATH" environment variable
 * 1) Go to the Effects tab of Preferences
 * 2) Check Rescan VST effects next time Audacity is started and click
 * 3) When you re-launch Audacity, the "Install VST Effects" dialog will appear where you can review the complete list of plug-ins to be loaded (including those you just added), uncheck any unwanted effects, then click  to launch Audacity including your new effects.



Audio Unit Effects
Audio Units (AU) are a system-level plug-in architecture provided on Mac OS X computers. Each time you launch Audacity it will load all Audio Unit effects that it detects. To add a new Audio Unit effect, place it in either of the following system plug-in directories:
 * ~/Library/Audio/Plug-Ins/Components (user plug-ins)
 * /Library/Audio/Plug-Ins/Components (system-wide plug-ins)

then restart Audacity. Newly added plug-ins will appear underneath the divider in the Effect menu. Audacity will not detect AU plug-ins in its own "plug-ins" folder where Audacity itself resides.