How to rid recordings
of hiss, buzz, and
NOTHING IS worse than recording a terrific
performance on an acoustic instrument, only
to realize during playback that hiss from
noisy mics and preamps has polluted the
irreplaceable track. Similarly, a once-in-a lifetime
electric guitar solo quickly loses its
luster when blighted by power-mains buzz.
And while sonic filth can often be avoided
in a properly grounded, soundproof studio
wielding high-end gear, it’s often completely
unavoidable in location recordings for film
and video shoots, where noise from cameras,
traffic, and HVAC systems rule the roost.
Let’s face it, every mix and post-production
sound engineer can benefit from having noise reduction
software in their armory.
|Fig. 1. iZotope Denoise provides controls for independently attenuating tonal and broadband
components of noise. Output Noise Only (at the top of the GUI) is checked to solo the removed noise.
This article will explore how to drain
the dreck from infected tracks to restore
their purity. I’ll focus on techniques using
the superb iZotope Denoise plug-in, which
is included in the company’s RX2 and RX2
Advanced noise-reduction bundles.
Identify the Enemy Find a section of your
track where noise exists alone. While the noise
plays back, click Denoise’s Learn button to
teach the plug-in the spectral content of the
racket you wish to eject. If the snippet of noise
is quickly followed by desired signal, you can
avoid including the latter in the scrap heap by
looping only the noise in your DAW during
the plug-in’s learning process. Click the Learn
button again to finish the analysis and ditch
the din. Boosting the Noise reduction control
increases the hush.
Go Solo You’ll get better results if you also
adjust Denoise’s other controls. Select the
GUI’s Advanced tab. Check the Output noise
only box to solo the removed noise while
adjusting the respective Threshold controls for
tonal (for example, buzz) and broadband (hiss)
components of the noise (see Figure 1). Find
the best settings to avoid including any desired
signal in the removed noise. If buzz is the
main problem, you can ostensibly treat it more
heavily by raising the Tonal Threshold and
Reduction sliders while leaving the Broadband
Reduction control set closer to 0.0dB. But don’t
be attached to the controls’ intended targets;
I sometimes find the broadband controls to be
more effective for removing buzz. Experiment
and see which control set works best for
the noise you want to remove. Regardless,
the golden rule is to never apply any more
processing than you need to make noise
unobjectionable—not necessarily eliminated—
while preserving the fidelity of desired signal.
Cranking the reduction sliders too high will
make the track sound muffled, less detailed,
and devoid of depth and nuance.
Keep Baby and Bathwater Separate
While you work, frequently toggle the Output
Noise Only function to assess what is being
removed (box checked) and the quality of
the remaining, desired signal post-processing
(box unchecked). If you hear watery-sounding
artifacts in the desired signal, carefully raise
the Global Smoothing control. You’ll know
you’ve raised it too far if you begin to hear
noise modulating in level when transients in
the program voice (with Output Noise Only
unchecked) or you hear bits of desired audio
signal when Output Noise Only is selected. Find
the best compromise setting, then raise the Fine
Smoothing control just enough to eliminate any
remaining artifacts and no higher.
The Denoise plug-in in the more fullfeatured
RX2 Advanced also provides a
Release control you can raise to reduce
artifacts. Be careful not to boost the release
time too much, though, or transients and
reverb tails will get munched.
Adapt If Necessary If you’re treating
tracks—such as those recorded outdoors
during a video shoot—in which the quality
of embedded noise changes over time, check
Denoise’s Adaptive Noise Learning box
(included only in RX2 Advanced; see Figure 2).
In this mode, the Learn button at the bottom
of the GUI serves no function, so ignore
it. Instead, adjust the Learning Time slider
(located to the right of the Adaptive Noise
Learning checkbox) for the best sound during
playback. The shorter the time value, the faster
Denoise will react to changing input signal,
nipping changes in traffic noise, for example, in
the bud. If you hear transients getting munched
or watery-sounding artifacts in desired signal
such as dialog, increase the learning time.
|Fig. 2. The Denoise plug-in in RX2 Advanced offers an expanded control set, including facilities for dynamically attenuating noise that changes over time.
This adaptive functionality is identical to
that provided by the checkbox labeled Adapt
to Changing Noise Profiles and its associated
Learning Time slider under the GUI’s Simple
tab. The two checkboxes are titled differently
for no apparent reason.
Put It In Neutral If the noise in some
frequency bands sounds more audible than
in others, increase RX2 Advanced’s Residual
Whitening control until the noise spectrum
sounds more neutral. (I find it helpful to loop
an isolated selection of noise while making
this adjustment.) Doing so will preclude your
having to crank the reduction sliders too
high in an attempt to improve results in one
frequency band while hammering the others
too hard. In cases where the noise spectrum
sounds really lopsided, you can create a
custom noise-suppression response curve—
containing up to 26 frequency nodes—in either
RX2 or RX2 Advanced.
Get Excited To preserve high-frequency
harmonics and prevent dulling, try raising RX2
Advanced’s Harmonic Enhancement slider
until the de-noised track sounds sufficiently
present. If you hear high-frequency noise
pumping, lower the slider to the point where
the modulation ceases. If that makes the
signal sound too dull again, try raising the HF
Synthesis slider, but be careful: Too high of a
setting can make the track sound glassy.
Clean Deeper Denoise is just one of the
noise-nuking weapons in RX2 and RX2
Advanced’s arsenals. Other plug-ins included
in the two bundles effectively discharge
AC hum, clicks, crackling noises, clipping
distortion, and even chair squeaks and dog
barks from tracks. Let the world rumble and
roar. There’s a plug-in for that.
Michael Cooper (myspace.com/michaelcooperrecording) has worked with
Academy Award-winning actor William Hurt
and the Emmy Award-winning ABC News
correspondent Barry Serafin. Cooper is a
contributing editor for Mix magazine.