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novocals.htm
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<html>
<head>
<title>The Truth About Vocal Eliminators</title>
</head>
<body bgcolor="#FFFFFF">
<p align="center"><font color="#808080" face="Arial"><big><big><strong>The Truth About
Vocal Eliminators</strong></big></big></font></p>
<p align="center"><font face="Arial"><em>by Ethan Winer</em></font></p>
<p align="center"><font face="Arial"><small>(This article first appeared in August, 1999
in <a href="http://www.prorec.com" target="_blank">ProRec</a>, the online audio magazine.)</small></font></p>
<hr color="#000000">
<p><font face="Arial"><font color="#808080"><strong><em>Note added February 26, 2005:</em></strong></font>
Please do not send email asking if you can hire me to remove the vocals from a track. I'm
too busy to take on new projects. If you don't have a suitable audio editor program, or
the techniques described in this article are beyond your skills, I suggest you buy Vogone
available <a href="http://www.mtu.com/basics/vocal-eliminator.htm" target="_blank">HERE</a>.
This is a reasonably priced commercial program that performs at least as well as the
manual editing described in this article.</font></p>
<hr color="#000000">
<p><font face="Arial">For many years the back pages of audio and recording magazines have
featured ads for hardware devices that claim to remove vocal tracks from a stereo
recording. Lately, several audio editing programs have also claimed to offer a vocal
remover feature. Is this possible? Is there really a magical way to remove the lead vocal
entirely from a commercial recording to create your own instant Karaoke backing tracks?
The short answer is No. Sometimes a vocal can be removed almost completely, but just as
often the results are disappointing. In most cases you'll be able to <em>reduce</em> the
vocal level, but some audible remnant of the original performance will probably remain.
Further, any process that changes the vocal track is sure to affect the other instruments
as well. In this article I will explain what vocal removal is all about and how it works.
I'll also describe the procedure and show how to do it yourself using common audio editing
tools.</font></p>
<p><font face="Arial" color="#808080"><strong>HOW VOCAL REMOVAL WORKS</strong></font></p>
<p><font face="Arial">You can reduce the level of a vocal (or other lead instrument) in a
stereo recording by taking advantage of how vocals are generally recorded: in mono and
placed centered in the mix. Since the vocal track is present in both the left and right
channels equally, you can, in theory, remove it or at least reduce its level by
subtracting one channel from the other. Instruments panned away from center will not be
removed, although the tone of those instruments will probably be affected. The basic
procedure is to reverse the polarity of one channel, and then combine that with the other
channel. Any content that is common to both channels will thus be canceled, leaving only
those parts of the stereo mix that are different in the two channels. Reversing the
polarity of an audio signal means that the parts of the waveform having a positive voltage
are made negative, and vice versa. (This is often incorrectly called reversing the phase.)
One important drawback inherent in vocal removal is that, by definition, it reduces a
stereo mix to mono. Since you are combining the two channels to cancel the vocal, you end
up with only one channel. However, there are ways to synthesize a stereo effect afterward,
and that will be described later.</font></p>
<p><font face="Arial"><em><font color="#808080"><strong>Important note added November 21,
2002:</strong></font> </em>You cannot remove vocals effectively if your source is an MP3
file. In order to remove vocals, the vocals in the left and right channels must be <em>exactly</em>
identical. Then when the polarity is reversed in one channel and the channels are
combined, anything common to both channels - what's panned in the center - is cancelled.
But MP3 encoding processes the two channels separately, so they are not identical enough
to cancel.</font></p>
<p><font face="Arial">It is impossible to completely remove a vocal or reduce its level,
without affecting other instruments in the mix. First, even though most vocals are placed
equally in the left and right channels, stereo reverb is usually added to vocal tracks. So
even if you could completely remove the raw vocal itself, some or all of the reverb is
sure to remain, leaving an eerie "ghost" image. If you plan to record yourself
singing over the resultant track, the new vocal can have its own reverb added, and you may
be able to mix your voice loud enough to mask the ghost reverb from the original vocal
track. Another limitation arises because vocals are not the only thing panned to the
center of the mix. Usually, the bass and kick drum are also smack in the middle, and those
get canceled along with the vocal! However, you can minimize this problem by rolling off
the lowest bass frequencies on one channel before combining it with the other. Since one
channel now has less low end than the other, the low frequency instruments will not
completely cancel. In fact, of the software programs I've seen that offer a vocal removal
feature, none alter the low end on one channel before combining, so the bass and kick are
eliminated along with the vocal.</font></p>
<p><font face="Arial">I developed the following procedures using two different types of
music. One is a tune from a friend's self-produced country music CD; the other is a cello
concerto I wrote and recorded in my home studio using live classical musicians from a
local orchestra. I created excerpts of these pieces in the popular MP3 format and they are
available here for downloading. This way you can compare the original recordings with the
processed result, to see for yourself how well vocal elimination works in practice.</font></p>
<p><font face="Arial" color="#808080"><strong>STEPS FOR REMOVING VOCALS</strong></font></p>
<p><font face="Arial">The most basic procedure is to load a stereo Wave file of the
original song into an audio editor program, flip the polarity of one channel and lower the
bass level somewhat, and then combine the left and right channels into a new, mono track.
I use Sound Forge 4.5 from Sonic Foundry, which includes all the tools needed to
manipulate audio files this way. Most other 2-track audio editors have similar
capabilities, and this technique will apply to those programs as well. Sound Forge lets
you load a single stereo file, manipulate the left and right channels separately, and then
combine them to mono all within one edit window. But for these instructions, I split the
channels into separate files to make each step easier to follow.</font>
<ol>
<li><font face="Arial">Load the original stereo file.</font></li>
<li><font face="Arial">Copy just the left channel to a new edit window.</font></li>
<li><font face="Arial">Copy just the right channel to another new edit window.</font></li>
<li><font face="Arial">* Reverse the polarity of the new left channel.</font></li>
<li><font face="Arial">* Apply a low end shelf cut starting at 200 Hz (at least 12
dB/octave) to the new left channel.</font></li>
<li><font face="Arial">Paste the processed left channel into the new right channel in <em>Mix</em>
mode (not Overwrite).</font></li>
<li><font face="Arial">Audition the result and, if it's acceptable, save it to a new Wave
file.</font></li>
</ol>
<blockquote>
<p><font face="Arial">* See the notes added at the end of this article.</font></p>
</blockquote>
<p><font face="Arial">It is possible that combining the two channels will exceed 0 dB, and
you will need to reduce the level of <em>both</em> channels a few dB. If you lower only
one channel, the two channels will not combine equally, and the vocal level won't be
reduced as much as possible. To roll off the bass frequencies, I used Sound Forge's
Parametric EQ in the high-pass mode set for 20 dB of cut starting at 200 Hz. (This filter
setting affects the lows, so why does Sonic Foundry call it high-pass rather than
low-cut?!) If you use Sound Forge, be sure to select the highest accuracy filter mode,
since how quickly the EQ is written to the file is less important than having the filter
perform exactly as you ask it to. Besides cutting the extreme low end on one channel, you
can optionally reduce some of the highs too. This lets you retain strings and cymbals and
other instruments that have treble content and are centered in the mix. In general, you
can cut those frequencies that are outside the vocal range - for male singers you need to
start the roll-off at a lower frequency than for females. Remember, the frequencies you
cut from one channel are the ones that will <em>not</em> be canceled when you reverse the
polarity and merge it with the other channel.</font></p>
<p><font face="Arial" color="#808080"><strong>A BETTER WAY</strong></font></p>
<p><font face="Arial">Rather than use a typical stereo audio editor program, a much better
approach is to separate the left and right channels into separate files and load them into
a multi-track audio recording program. The main advantage is that you can more easily
adjust the channel levels to fine tune the process for the most complete vocal
cancellation. This also lets you experiment with different high and low frequency turnover
points, assuming your multi-track software offers EQ for the tracks. Start with just the
very lowest and highest frequencies removed, and then slide the cut-off frequencies closer
to the middle until the vocal starts to leak through. Again, you are combining the two
mono tracks at approximately equal levels - but with the polarity reversed, and the
extreme highs and lows rolled off on only one channel. I use SAW Plus, which has EQ and
polarity reverse effects built in. These effects are non-destructive and can be adjusted
in real time while the left and right channel Wave files are playing. So all I had to do
was extract the Left and Right files from the original stereo Wave file, load those into
separate tracks in SAW, and add polarity reverse and low-end shelf cut at 200 Hz to the
left channel. Once you are satisfied that you have removed as much of the vocal as
possible and with minimum damage to the rest of the track, save the mix to a new Wave
file.</font></p>
<p><font face="Arial">One useful tip is to reduce the number of playback buffers if your
multi-track recorder software allows that. Normally, the more buffers you have the better
because that avoids "stuttering" when playing back many tracks at once. But the
trade-off is that more buffers yields a longer time lag between when you change a volume
level or EQ setting and when you hear that change. So when working with only two mono
tracks for removing vocals, I set SAW to use the minimum number of buffers, thus making my
mix changes audible immediately.</font></p>
<p><font face="Arial">Earlier I mentioned that removing vocals always yields a mono sound
file because the left and right channels are combined as part of the process. There are
several ways you can synthesize a stereo effect to recreate some of the lost ambience. I
used the BlueLine series of plug-ins by digilogue, available in a fully functional
shareware version ($35 to purchase) from the author's web site at <a
href="http://www.digilogue.de" target="_blank">www.digilogue.de</a>. These plug-ins are
provided in the universal DirectX format and also as VST versions for use with Steinberg's
Cubase. I used the BlueLine Stereo plug-in, which did a great job of recreating a stereo
effect on the mono result files.</font></p>
<p><font face="Arial">You can also create a fake stereo image using equalization. Split a
mono track into two identical left and right channels, and then equalize each side
differently. One method is to apply a 10-band graphic equalizer to each channel, and then
boost and cut alternate bands on each channel. That is, on the left channel you apply 6 dB
of boost at 62 Hz, the same amount of cut at 125 Hz, boost at 250 Hz, and so forth. The
right channel is then cut and boosted by the same amounts, but at the frequencies opposite
the left channel: Where the left channel is boosted the right is cut, and vice versa.</font></p>
<p><font face="Arial">Two final items are worth mentioning. First, if your multi-track
software requires DirectX plug-ins for EQ and polarity reversal, the inherent delay will
prevent the desired cancellation and all you'll get is a phased sound with the vocal still
present. In that case you should reverse the polarity and roll off the low end in a stereo
editor that writes directly to the file, and load the result back into your multi-track
recorder. I'll also mention that it is possible to cancel a vocal from a stereo file while
keeping the original stereo image. If you create a mono Wave file that is a simple mix of
both the left and right channels, you can reverse its polarity and mix it with the
original stereo recording. This cancels the vocal and other centered instruments, and
reverses the left and right channels as a side effect. Although this should be superior to
my method of reducing the mix to mono, in practice it did not work as well. More of the
vocal leaked through, and the non-centered instruments were partially canceled.</font></p>
<p><font face="Arial" color="#808080"><strong>THE BOTTOM LINE</strong></font></p>
<p><font face="Arial">Does vocal removal really work? Is it worth the effort to even try?
I'll leave that for you to decide. Following are two pairs of MP3 clips containing Before
and After versions of my attempts. The first piece (265 KB for each MP3 file) is <em>Rollin'</em>
from the CD <em>20 Years Late</em> by Tom Schulz. Click <a href="http://www.ethanwiner.com/TomBefor.MP3">here</a> to
download a 34-second MP3 clip of the original recording, and click <a href="http://www.ethanwiner.com/TomAfter.MP3">here</a>
for the result after removing the lead vocal track. The second selection is from my <em>Concerto
for Cello and Orchestra in A minor</em> (313 KB per file). Click <a href="http://www.ethanwiner.com/CelBefor.MP3">here</a>
to download a 38-second MP3 fragment of the original, and <a href="http://www.ethanwiner.com/CelAfter.MP3">here</a>
for the version with the solo cello removed from the track.</font></p>
<p><font face="Arial">Both of the After tracks were processed in SAW Plus as described
previously, and then a stereo effect was synthesized using the BlueLine Stereo plug-in. I
rolled off the lows starting at 200 Hz, but didn't bother experimenting with the highs. As
you can tell I was quite successful removing Tom's lead vocal, mostly because so little
reverb was added to his voice. In fact, before I rolled off the low end on one channel to
bring back the bass and kick, the vocal was practically inaudible. All that remains now is
a muffled hint of his voice. Of course, the bass and kick have lost definition in the
process, since all but the deepest components were canceled along with the vocal. With the
cello recording you can clearly hear the ghost reverb, and the beginning passage also
leaks through because those notes are lower than the 200 Hz cut-off point. I could have
lowered the EQ frequency, but that would have removed more bass content from the rest of
the track.</font></p>
<p><font face="Arial"><font color="#808080"><strong>* <em>Added November 14, 2004:</em></strong></font>
I've been getting a lot of emails asking how to reverse the polarity and roll off the low
end of one channel in Sound Forge. Here are the specific steps using Sound Forge version
6:</font></p>
<p><font face="Arial">Double-click in the upper portion of the Wave file view to highlight
the entire length of just the left channel. If both channels turn dark you didn't have the
cursor low enough when you double-clicked. Then from the Process menu select Invert/Flip.
Next, apply a low frequency shelf to roll off below 200 Hz. From the Process menu select
EQ, and choose Paragraphic from the sub-menu. Check the box at the bottom labeled Enable
Low Shelf, then either adjust the slider at the right until the display reads 200, or
simply type 200 in that field. Finally, move the smaller slider all the way to the left
until the display reads -Inf.</font></p>
<hr color="#000000">
<p align="center"><font face="Arial"><small>Entire contents Copyright (c)1999 Ethan Winer.
All rights reserved.</small></font></p>
</body>
</html>