Effect Menu
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- Peter 26Nov09: Checked for spelling/typos/consistency.
- Peter 28Nov09: Checked links.
Classes of Effect
There are six classes of effects - the built-in Effects, and five classes of plug-in effect which allow you to download and install additional effects. All classes of effect are applied in the same way. The six effects classes are:
- Built-in Effects
- VST Effect Plug-ins
- Nyquist Effect Plug-ins
- LADSPA Effect Plug-ins
- VAMP Plug-ins
- Audio Unit Plug-ins (Mac only)
List of Built-in Effects
Amplify...
This effect 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.
BassBoost...
This is a smooth filter which can amplify the lower frequencies while leaving most of the other frequencies alone. It behaves just like the bass control on a stereo.
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.
Click Removal...
Click Removal is designed to remove individual clicks on audio tracks and is especially suited to declicking recordings made from vinyl records, without damaging the rest of the audio.
Compressor...
Compresses the dynamic range by making the loud parts softer. If make-up gain is applied the effect will also make the quiet parts louder.
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 linear fade-in to the selected audio - the rapidity of the fade-in depends entirely on the length of the selection it is applied to. For a more customizable logarithmic fade, use the Envelope Tool on the Tools Toolbar.
Fade Out
Applies a linear fade-out to the selected audio - the rapidity of the fade-out depends entirely on the length of the selection it is applied to. For a more customizable logarithmic fade, use the Envelope Tool on the Tools Toolbar.
Invert
This effect flips the audio samples upside-down. This normally does not affect the sound of the audio at all. It is occasionally useful, for example when the left and right channels of a song both contain equal amounts of vocals, but unequal amounts of background instruments. By inverting one of the channels and not the other and then converting from stereo to mono, the vocals will cancel each other out, leaving just the instrumentals. This only works if the exact same vocal signal is present in both of the channels to begin with.
Leveller...
The Leveller effect makes quiet passages louder and loud passages quieter. It does this in a way that is different from the Compressor effect. As a result it does add some distortion to the processed audio. The only way to be sure if the effect does what you want is to try it. For example, applying this effect twice at its Heaviest setting on a normally-recorded voice can produce an "air traffic controller" effect.
Noise Removal...
This effect is ideal for removing 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...
This brings up a dialog where you can enter Nyquist commands. Nyquist is a programming language for producing and processing audio. For more information see Audacity and Nyquist and Nyquist in Audacity.
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 very short click, pop, or other glitch no more than 128 samples long.
Repeat...
Repeats the selection the specified number of times.
Reverse
This effect reverses the selected audio temporally; after the effect the end of the audio will be heard first and the beginning last. Some people reverse small portions of audio to make inappropriate language unintelligible, while others believe you can hear subliminal messages if you listen to speech backwards. You can also create interesting sound effects by recording natural events and reversing the audio.
Sliding Time Scale / Pitch Shift
This effect allows you to to make continuous changes to the tempo and/or pitch of a selection. For example, you could set the initial tempo to -50% and the final tempo to +20%. Or you could set the initial pitch to +3 semitones and the final pitch to +1 semitones. Or you could do both at once.
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.
This effect 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 WahWah effect automatically adjusts the phase of the left and right channels when given a stereo recording, so that the effect seems to travel across the speakers.
VST Effects
- To use a VST plug-in effect, put the effect in the directory (folder) called "plug-ins", which should be in the same directory where Audacity resides. If there is no directory, create one.
- Launch Audacity and go to the Effects tab of the Preferences dialog. Check Rescan VST effects next time Audacity is started. Click the OK button.
- Quit and re-launch Audacity - any plug-ins you added will appear in the Effect menu.
- The Rescan VST effects next time Audacity is started option will now be un-checked.
Since scanning for VST effects slows the launch process, Audacity can launch faster if it doesn't have to do this scan unless the user explicitly asks for it.
Nyquist Effects
ToDo Not a priority for 2.0, but needs a little more here:
- where to get other Nyquist plug-ins
- where to get docs
- the debug button in Nyquist effects
- Nyquist workbench
- To use a Nyquist effect, put the effect in the directory (folder) called "plug-ins", which should be in the same directory where Audacity resides. Upon installation, some Nyquist scripts are included, so you needn't worry about creating this directory.
- The next time you launch Audacity, any plug-ins you added will appear in the Effect, Generate or Analyze menus.
Clip Fix ...
Clip Fix attempts to reconstruct clipped regions by interpolating the lost signal.
Cross Fade In
Despite the name this effect does not do an automatic cross fade between two tracks or clips. Instead it applies a curve that is different from the one used by the Fade In effect. The curve used is one that will result in equal volume throughout the fade once the faded in and faded out regions are mixed.
Cross Fade Out
Despite the name this effect does not do an automatic cross fade between two tracks or clips. Instead it applies a curve that is different from the one used by the Fade Out effect. The curve used is one 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 cutoff frequency and attenuates frequencies below its cutoff frequency.
Low Pass Filter...
Passes frequencies below its cutoff frequency and attenuates frequencies above its cutoff frequency.
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...
Bill: I don't know what I could add to what is in the help section of the dialog, and in the wiki
For reference, here's what you get when you select "Help" from the dialog:
Vocal Remover requires a stereo track and works best on audio in a lossless format like WAV or AIFF rather than a compressed, lossy format like MP3. If your song is on a CD, use a program like CD-ex to rip it to WAV or AIFF before using Vocal Remover.
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. Vocals are often recorded this way. When one channel is inverted and then both panned to center, any audio which is identical in both channels is cancelled out, so becomes inaudible. This means that if audio you don't want to remove also happens to be center-panned, it will be cancelled out along with the vocals. Drums are an example of audio that is often center-panned and can thus disappear when vocals are removed. However, if the vocals and other center-panned parts of the audio differ from each other in pitch (and thus in frequency), removing only selected frequencies from the audio can solve such problems.
Vocal Remover therefore has three choices of removal method. 'Simple' inverts the entire frequency spectrum of one channel. If all the audio except the vocals is panned hard away from center, this will work the best. If some of the other audio is common to both channels, this choice may remove too much music, in which case try the remaining options. 'Remove frequency band' removes frequencies in a band whose upper and lower limit you specify in the 'Frequency band...' box. Try this choice, entering the approxmate frequency range of the vocals, if they are apparently at a very different pitch than the other audio (for example, a high female voice). 'Retain frequency band' removes only those frequencies lying outside the limit you specify, retaining the others. This choice can help if there is audio of a particular frequency range (such as low drums or bass) that is lost when using the other methods. Simply enter the approximate frequency range of the audio you wish to retain.
A tutorial would be difficult to do properly without audio samples to show what can go wrong.
Attempts to remove center-panned vocals from a stereo track. Help text is available from within the dialog.
Vocoder...
Synthesizes audio (usually a voice) in the left channel of a stereo track with a carrier wave (typically white noise) in the right channel to produce a modified version of the left channel. Vocoding a normal voice with white noise will produce a robot-like voice for special effects. Other carriers can be used for subtly different robot voices, such as a sawtooth tone or a synthesized string chord.
Vocoder only works on unsplit stereo tracks. Example steps to make a stereo voice sound like a robot:
- Record or import your stereo voice track
- Click the to split the stereo track into left and right channels
- Click the Track Panel of the right channel to select it, then click and choose White Noise
- On the left (upper) channel, click the to make an unsplit track again
- Click the Track Panel once more to select the track, then . Try with the default settings at first. If you want to make the voice sound less intelligible, reduce the number of vocoder bands and vice-versa.
If your voice track is mono:
- Click to add a new track underneath your voice track
- Click and choose White Noise
- Then follow steps 4 and 5 above
LADSPA Effects
LADSPA (Linux Audio Developer's Simple Plugin API) effects were originally developed for the Linux platform, but ports of some plug-ins are available for Windows and OS X as well.
Three sample LADSPA plug-ins are included with Windows and Mac builds of Audacity:
Hard Limiter...
An extreme compressor effect.
GVerb...
A reverb plug-in. Tips and example settings are available on our Wiki.
SC4...
A stereo compressor with a variable envelope follower for RMS / peak behaviour.
VAMP Effects
Vamp is a plug-in format developed by Chris Cannam (author of Rosegarden and Sonic Visualiser) for viewing and analysing the descriptive contents of music audio files. Typical things that a Vamp plug-in might calculate include the locations of moments such as note onset times, visual representations of the audio such as histograms, or curve data such as power or fundamental frequency.
Vamp can process selected audio and produce a label track with particular parts annotated with labels, based on various criteria.
Currently Audacity only loads plug-ins from the standard directories defined by the Vamp SDK, not any of the Audacity-specific directories. These are:
- Any directories listed in the VAMP_PATH environment variable (all platforms)
- On Windows, %%PROGRAMFILES%%\Vamp Plugins (i.e. a directory named "Vamp Plugins" within the system Program Files directory, however localized and on whatever drive is relevant to this install of Windows)
- On Mac OS X, ~/Library/Audio/Plug-Ins/Vamp (user plug-ins) and /Library/Audio/Plug-Ins/Vamp (system-wide plug-ins)
- On anything else but mainly Linux, $HOME/vamp, $HOME/.vamp (user plug-ins) and /usr/local/lib/vamp, /usr/lib/vamp (system-wide plug-ins).
Audio Unit Effects
Audio Units (AU) are a system-level plug-in architecture provided by Mac OS X. Audacity supports Audio Unit plug-ins, and will find them in Audacity's Plug-ins folder which should be in the same directory where Audacity resides. Upon installation, this folder should already exist. Audacity will also look in the standard plug-in directories for Mac OS X: ~/Library/Audio/Plug-Ins/Components (user plug-ins) and /Library/Audio/Plug-Ins/Components (system-wide plug-ins).
