Hello eric_boston,
Thanks for your question!
First, let's further define "crossfade". Sweetwater Sound's glossary
(http://www.sweetwater.com/insync/word.tpl?find=Crossfade) states:
"Crossfade
A technique commonly used in editing audio. One sound is faded out as
another fades in, allowing for a smooth transition between the two.
Crossfading is also common in samplers, where it is used to smooth
loop transitions (crossfade looping), and sound design to create
hybrid sounds (one sound morphing or turning into another). While we
often think of this as a digital process, audio engineers have been
using two channel faders on a mixing console to crossfade between two
signals or tracks for many years. "
What I believe you are going to find is that crossfading is an art
form and there are few rules of right or wrong. Once one understands
and becomes proficient at a technique, the rules disappear and the
techniques can be used in new, fresh and creative ways. Parameters
such as the length of a crossfade are artisitic judgements in the end.
I first searched for digital +crossfade +technique and found the
following pages and information:
My friend, David Gans, who has been a daily user of digital audio
workstations for many years, says at
http://www.levity.com/gans/mwec.html :
"Butt-splices and quick crossfades are the hammer and ripsaw of audio
editing; hard-disk audio gives you amazingly fine-grain control of
everything, fulfilling the promise of the "personal computer"
handsomely by eliminating huge amounts of tedium, greatly improving
control of the result and vastly expanding the creative
possibilities."
In speaking of his particular workstation at the time, Sonic
Solutions, he says:
"With Sonic Solutions, you can design crossfades up to a hundred
seconds long, controlling the length and shape of either side
independently or with perfect symmetry, depending on whether you're
looking for something imperceptible or "morphing" one sound into
something different for musical, dramatic or comedic effect. In my
business, editing live concert performances that sometimes come from
imperfect source tapes, digital audio means I can experiment with
various ways to cover an edit rather than choosing just one of many
promising pairs of edit points, as it was in the quarter-inch days,
and hoping for the best."
Paul White, in his technique of stereo editing chapter, "chopping and
changing", ( http://www.sospubs.co.uk/sos/mar00/articles/stereoedit.htm
) talks about using a crossfade technique to remove pops and clicks
and says:
"There's some very sophisticated software available for identifying
and removing clicks automatically, and if you have access to one of
these dedicated packages I'd suggest you try it, to see if it can do
the necessary invisible mends...
Even if you don't have specialised click-removing tools, where clicks
are readily identifiable and not too frequent it's generally possible
to remove them manually, using simple edits and crossfades. This
technique is useful for clicks caused by electrical interference that
cause effects lasting several cycles of the audio waveform.
First, create two regions, one stopping a few cycles before the click
and the next starting a few cycles later.
Line up the edit points so that they occur on zero crossings and are
in phase.
Use a short crossfade to smooth the join. If you're lucky, the tiny
portion of audio you've lost in getting rid of the click won't throw
the timing out.
The important thing to watch here is that you don't make the edits too
close to the click you're trying to remove -- otherwise when you
create your crossfade the click will be allowed to creep back in. The
same is true if you make the crossfade too long, as you can see from
Figure 1a. If you're planning to do a 10mS crossfade, for example, you
need to leave at least 5mS' worth of material either side of the
click."
You will find much more interesting information and techniques on his
pages.
At http://www.transom.org/tools/editing_mixing/200111.voiceediting.jtowne.html
, Jeff Towne talks about Digidesigns Pro Tools, probably the widest
used professional digital editing package. He mentions yet another use
and techniques for crossfades when fading in or out to silence:
"The very beginnings and endings of voice tracks are often problematic
as well. There may be a click at the region boundary, out-of or into
silence, or there may be ambience behind the voice that makes a hard
edit sound clunky. Sometimes even subtle, low-level background sounds
can make a hard edit just sound "wrong" even if there's not an obvious
ambience shift. Never fear, fades can help you here too."
You will find his complete technique at the above mentioned page.
DJ mixers for live performance always include a crossfade function to
allow a smooth transition from tune to tune at a dance club or event.
One critical additional technique often needed in this application is
matching the tempo and rhythm while crossfading from tune to tune.
Simulating and embellishing the crossfade technique of a DJ mixer
using a software package called "Live" is discussed at
http://216.239.53.100/search?q=cache:ECXgtu0QsjoC:www.ableton.com/content/content-objects/Tutorial_Djing.PDF+audio+%2B%22crossfade+technique%22&hl=en&ie=UTF-8
:
"Quick Crossfading techniques using the mouse and keyboard
A DJ mixer has a crossfader. This fader allows the DJ to
simultaneously bring one volume level down while bringing another
volume level up usually to "fade" between songs or to momentarily
mute one channel for some sort of special scratch effect. Live has no
crossfader, but there are many ways to manipulate the channel faders
and mute keys in tandem to get similar sounds. Mixing transitions that
take place in longer than a bar or two are much technically easier,
since the DJ can basically just use the mouse to nudge one fader up a
little bit, then nudge another fader down a little bit, etc... until
the new track is mixed in and the old track is mixed out.
The quick moves described below take a bit more practice, but their
main practical advantage is that they do not require the tracks to be
beatmatched extremely well - since the transition will hopefully
happen too fast for anybody to notice.
Quick "Transform" Fade: This emulates the instant switching from one
track to another that can be executed with a "hamster" switch, a
transform switch, or a crossfader with an extremely steep transition
curve, on a DJ mixer. There is no point not even a brief one at
which the two tracks are playing simultaneously. This technique is
very easy with Live: if one track is playing and the track to
-be-switched-to is muted, simply press the two track mute buttons
simultaneously.
Steep Crossfade: This emulates the near-instant switching from one
track to another that can be executed with the quick manipulation of
channel faders, or a crossfader with a steep transition curve, on a DJ
mixer. There is a brief moment about a quarter of a beat long -
during which the two tracks are playing simultaneously. This technique
is relatively easy with Live; the setup is that one track is playing
and the track to be switched to is muted. It's very similar to the
"transform" fade, except that the "second" track is unmuted a split
second before the "first" track is muted. The result is that both
tracks are playing simultaneously for a very brief time. This gives
the listener the auditory illusion that the two tracks are being
crossfaded between. The longer the tracks are played together
simultaneously (though this time should rarely exceed 2 beats), the
smoother the crossfade will seem. Smoother Transitions using one
channel fader and the mute keys: If the "Steep Crossfade" technique is
combined with the manipulation of the second track's channel fader,
the auditory illusion of a smoother transition is possible. The
procedure is to begin executing a Steep Crossfade, but lengthen the
time that both tracks are playing simultaneously to 2-4 beats. At the
beginning of the "simultaneous time", the second channel fader should
be about 20-30dB down. This fader should be quickly raised via the
mouse, while the other hand is used to operate the mute buttons. By
the end of the "simultaneous time", the second channel fader should be
up to 0dB. This technique can work the other way, too: instead of
bringing up the second channel fader during the simultaneous time,
bring the first channel fader down. While raising the second fader
draws a lot of attention to the new track, lowering the first fader
instead gives the impression that "the second track was playing in the
background all along". "
While searching "crossfade settings" to find additional specific
techniques used in audio crossfading, I uncovered the following sites:
http://service.real.com/help/library/guides/jukebox2pl
Real Jukebox, a very popular internet audio / video program talks
about suggested settings for replacing the space between tunes with
smooth crossfade transitons as well as fade-ins and fade-outs fro
music playback of Real Audio tracks on your hard drive. Though these
settings are specific to this software program, take note that their
interface clearly delineates the parameters for crossfading you have
at your disposal which is the length of the crossfade in seconds, the
timing of the fadeout of the original material and fade in of the new
material. This program does not offer you control over the levels of
the individual tracks you are fading.
And lastly, a copy of Adaptec's owner's manual for JAM, a very popular
CD burning tool, is available here:
http://classes.yale.edu/vima/SoftwareDocs/archiving.extracting/Jam2.1Manual.pdf
They have a VERY good description of Crossfades in Chapter 8 and
define and suggest settings for the following:
Seamless transition
Overlapping Crossfades
Overlapping Pre-Splice Crossfade
Overlapping Post-Splice Crossfade
Extending Crossfade
They note that Jam allows the following seven types of Crossfades:
Hard Cuts
Linear Crossfades
Equal Power Crossfades
Slow Out, Slow In Crossfades
Fast Out, Slow In Crossfades
Slow Out, Fast In Crossfades
Overlapping Cut Crossfades
I think you will find this to be one of the best descriptions of
techniques and setttings for cross fading.
After reading a bit, I suggest you listen to available music, say Pink
Floyd's Dark Side of the Moon for examples of crossfading, and then
experiment. As you will see (or hear), there really is no right or
wrong and just that some crossfades will be more interesting or more
pleasing to your ear.
Enjoy your exeperimentation! And if anything above happens to be
unclear, polease feel free to ask for clarification.
Regards,
-=clouseau-ga=- |
Clarification of Answer by
clouseau-ga
on
02 Sep 2002 12:50 PDT
Hello again,
Sorry, the Real link did get truncated. The correct link should be :
http://service.real.com/help/library/guides/jukebox2plus/htmfiles/playing.htm
Your request for clarification states:
"My primary interest is in crossfades for mastering purposes --
combining portions from multiple recording takes into one final
version."
I'm unsure what you mean here. I could interpret this to be combining
separate takes of the same tune and inserting portions from several
different takes to create a final version of one song. But I don't
believe this is what you really are looking to do. This would require
insert editing rather than cross fading, which is an entirely
different technique. Though as you have seen from the above,
crossfades CAN be used effectivley in certain types of insert editing,
but not as a general rule.
What I believe you are really asking is in regards to combining
individual tunes from multiple recording sessions into a finshed
product that segues smoothly from tune to tune.
If I am correct, then important considerations are first being sure
that your average playback level is very close for all tunes in the
project, both as average levels readings and as peak readings if you
need to raise the levels of any tune to be sure that no clipping
occurs. This is a common step in the mastering process.
Then, I would trim the final and/or opening segments of the tunes to
be crossfaded as needed so that the tail out or fade in length would
not be excessive. Most digital audio programs allow non-destructive
editing so that you are really not discarding the unused material,
just rearranging it on other audio tracks, so trimming to a bit longer
than you anticipate using on the fade out and a bit before you
aniticipate hearing the fade in will make the process slightly easier
for you to setup and test with different timings and settings. As long
as the program you are using is, indeed, non-destructive, then simply
cutting at these points is all that is needed as you will be out and
well below audibility before the abrupt cut and starting to fade in
well after the chosen starting point of the next tune.
Deciding how much overlap or "mixing" of the tunes in the crossfade,
or to "replace" is basicly an artistic judgement, however I did some
additional searching for you and found the following:
The Secret Life of Audio Crossfades
by Andy Somers
at http://www.editorsguild.com/newsletter/SepOct99/tipaudio_cross.html
has a very interesting discussion of sound levels as regards
crossfades. He details 3 common fades: -3, -6 and -9. These names
refer to the cross point of each fade, or the level of the audio at a
point halfway into the fade. In the case of a crossfade, it's the
point where the levels of the two pieces of audio being crossfaded are
equal.
Now look at Figure 2A. Here we see two pieces of exactly the same
audio. If we were to play them both at exactly the same time (in
perfect phase), the volume would double, or increase the level by 6
dB. Therefore, if we want to have a perfectly smooth crossfade between
these two identical pieces of audio, we'd use a -6 dB crossfade. Then,
at the cross point, both pieces of audio would be lowered by 6 dB,
meaning the net result would be a difference of 0 dB and the fade
would be perfectly smooth.
He continues:
"Generally, though, we don't crossfade into the exact same piece of
audio. We are typically trying to cross into a new and different sound
clip, and we want to do this as smoothly as possible."
What follows is a brief, but very good explanation of setting levels
for crossfades and ramps that I think you will find helpful.
You later ask in your Request for Clarification :
"or how to decide whether to go with a "mixing" vs. a "replace"
crossfade
option."
By definition, all crossfading mixes two different signals with some
degree of overlap (even if it is mixing silence as one of the sources)
until the first signal is "replaced" by the second signal totally. So
your decision is not whether to mix or replace (which actually refers
to another digital editing technique analogous to punch-in punch-out
with tape), but how to mix so as to create the transformation you
envision.
I hope this clarification has been helpful.
-=clouseau-ga=-
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