Fade and Crossfade
Fade effects frequently produce a transition from silence (fade in) or a transition to silence (fade out) but may equally refer to a transition from one volume level to another quieter or louder level. A crossfade is when one section of audio fades out while another fades in.
- Gale 16Aug14: I have not proofread it, but isn't it very long by our standards ? Should Sections 6 and 7 be on their own page? To aid discovery I would think a FAQ is required to link to this page and also to link to Fades and to Envelope Tool. It is not uncommon for users to ask "Do I have to use amplify in small sections to gradually make the sound quieter?".
- Steve 21Aug14: I think I've now got all of the "exponentials" and "logarithms" the right way round now.
- Peter 21Aug14: Now that Steve has sorted out logarithmic/exponential I went ahead and made the sub-pages that gale suggested - actually now sections 7 & 8 as Steve created an additional section.
ToDo-2 Do we want to consider moving section 9 off onto its own page too? My vote would be to do this?
- Gale 21Aug14: Seems sensible to split off #9 now, yes.
- Peter 22Aug14: I split of #9 to Other plug-ins and tools for fades and tidied it up a bit.
- Gale 22Aug14: Thanks. Having looked at it, I think it could be better to move the "remove clicks" and "presentation" use cases back here. Those use cases don't depend on using those "other tools". If we don't move the use cases back, then we must fix the links "exponential shape fade" and "sine curve fade" in the last section on that page so they point here.
If we want a separate (now much shorter) section for "Creating Fades with the Envelope Tool" it seems to me it should be near the top of this page (explaining that Envelope Tool may/should be used for all fades listed here except linear). Or possibly the Envelope Tool section could be segued into the text of Exponential Fade.
I would tend to favour a section first of all having a summary of the basic GUI tools to make a fade, mentioning what type of fade each can make. I would definitely want to mention Adjustable Fade in that section. I assume the reason we don't mention it is that Adjustable Fade did not exist when we started this page on Wiki.
Contents
- Linear Fade
- Exponential Fade
- Logarithmic Fade
- Equal Power Fade
- Sine Curve Fade
- DJ Crossfade Curve
- Creating Fades with the Envelope Tool
- Creating a Crossfade
- Using a fade to remove a click from the start of a sound
- Adding an extract of music to a presentation using fades
- Other plug-ins and tools
Linear Fade
This is the most simple type of fade where the level rises or falls at a constant rate. A linear fade in from silence is easily created in Audacity using . A linear fade out to silence is created using .
The "shape" of a fade is commonly described in terms that suggest the appearance of a constant level signal that has had the effect applied to it. For example, if a linear fade in is applied to a generated tone, the fade can be seen to follow a straight line from silence up to the original level.
Exponential Fade
This is another very common fade type. Its popularity stems from the fact that it closely models the way in which sounds naturally decay. For example, comparing the waveform of a gunshot recording with that of a bell, we can clearly see that although the time scales are very different, the shape of the sound as it decays is very similar:
In Audacity, the Envelope Tool produces exponential fades.
A similar (but not identical) fade shape may be produced by applying a linear fade several times to the same selection. For example, here is a fade created by applying the Fade Out effect, then repeating it three times using the CTRL + R shortcut (Repeat Last Effect).
Exponential curves may also be used as a fade-in.
Logarithmic Fade
Essentially the same as an exponential fade, but curving the other way.
Equal Power Fade
If one sound is fading out while another sound is fading in, this is called a crossfade. A common problem when crossfading two sounds using linear fade effects is that the volume level may drop a little midway through the transition. To mitigate this problem it is common to use a fade shape that, compared to a linear fade, bows up in the middle, so that the volume level stays a little higher in the middle of the transition. One of the most commonly used crossfade shapes is an "Equal Power Fade"; so called because the average power (and hence loudness) remains fairly constant during a crossfade transition for music and other uncorrelated sounds. The next image shows two tracks, one with white noise and one with pink noise that are crossfading using Equal Power Fades.
Sine Curve Fade
A raised sine curve (or cosine curve) is based on the shape of a sine wave. This fade type is often used for fading out music as it produces a smoother, more musical sounding fade out than a linear fade. It is also sometimes used as an alternative to the Equal Power Fade for crossfading as it avoids the possibility of the peak level increasing during the crossfade (Like linear fades, it produces an "Equal Gain" crossfade).
DJ Crossfade Curve
DJ Mixers have a crossfade slide control that is essentially two faders back to back in one unit. Moved in one direction it will fade in source A and fade out source B, and when moved to the other extreme it will fade out source A and fade in source B. Early DJ mixing desks crossfaders produced a (roughly) equal power crossfade, but in response to demand from DJs, other fade shapes were developed that have a more pronounced curve, thus making the mix more pronounced during the transition. More information about the history of DJ crossfaders can be found on the Rane web site.
Modern DJ mixers provide a curve control to provide adjustment of the fade taper contour. The image below compares the shapes of an equal power fade with a high curve fade that is similar to what would be achieved by setting the curve control fairly high on a DJ mixer's crossfader.
Creating Fades with the Envelope Tool
The main advantage of creating fades with the Envelope Tool is that it is non-destructive. The envelope may be changed or removed at any time with no loss to the audio data.
See this page for details of how to use the Envelope Tool to create a fade.
Creating a Crossfade
The purpose of a crossfade is to produce a smooth transition between two sections of audio. The two sections overlap and as one section fades out the other fades in. This technique is commonly used by DJ's, for "compilation" tracks and mashups. The use of crossfades is not limited to joining pieces of music, but can be used in many other situations where a smooth transition is required, including editing speech recordings, extending songs, creating loops for audio sequencers, repairing damaged recordings and much more.
See Creating a Crossfade for details of how to make a crossfade.
If a sound starts suddenly, there will often be a noticeable click at the beginning. This is due to the waveform suddenly jumping from silence to the start of the waveform. This "jump" is often visible by zooming in closely on the start of the sound so you can see the original sample dots:
Applying a short, linear fade in can eliminate the click by smoothing the transition from silence to the start of the sound.
Adding an extract of music to a presentation using fades
Whether PowerPoint, OpenOffice Impress, a slide show for YouTube or any other audio-video presentation, it is often desirable to include audio clips within the presentation. Rather than simply cutting a recording to the required length, applying a fade in and fade out to the audio clip can add a touch of professionalism to the production.
The duration of the fade as well as the shape of the fade are crucial to the overall effect. Typically an audio clip will have a relatively short fade in and a longer fade out, but there are no hard and fast rules. Audacity allows you to experiment with different fade lengths. When preparing audio clips for use in your presentation you can export several versions with differing fade lengths, then when putting together the presentation, try your alternative versions and use whichever you most like.
Fading in music with an exponential shape fade is often very effective as you get a hint of the music first, then it rapidly fades to full volume. For fading out music, a sine curve fade often works well.
See also: Mixing
Other plug-ins and tools
See this page for details of additional tools and techniques using fades. The page carries information on the following:
- Fade In and Out
- Text Envelope
- Creating Fades from the Nyquist Prompt
- Using a fade to remove a click from the start of a sound
- Adding an extract of music to a presentation using fades
Additional material to be added:
- Peter 21Aug14: But not on this page - these topics are likely to be tutorials in their own right. I have copied these suggestions to the ednote on the Tutorials page.
