Algorithmix ScratchFree and
A Software Review By Read G. Burgan
Occasionally during the early 70’s, AT&T would forget to switch our NPR line
to the Texaco Metropolitan Opera line on Saturday afternoons. At the last
minute I would call AT&T long lines and end up patching the Metropolitan
Opera directly from a phone to our audio console. Quality? A tin can and
waxed string couldn’t have sounded much worse.
By the end of the 70’s, the Met Opera and almost everything else were coming
by satellite in stereo. Improvement? Like going from the Stone Age to the
Nuclear Age in 60 seconds or less.
In the decades that have followed, ever improving quality has become the
watchword for both AM and FM broadcasters. Digital audio restoration
software and hardware have been some of the means of achieving higher
Over the past 11 years, I have reviewed many digital audio restoration
software packages. During that time, they have improved considerably.
Despite incremental improvements, I rarely find a new package that has
causes me to replace the software tools that I have been using. Until now.
Recently Algorithmix has released two new digital audio restoration plug-ins
for Windows compatible audio editors. Algorithmix is a German based company
that licenses its algorithms to other companies. For example, Waves Ltd.
licensed some of Algorithmix’s algorithms for its original noise reduction
ScratchFree and NoiseFree are available as DirectX or VST plug-ins. There
are differences in the DirectX and VST versions. More about that later.
ScratchFree is designed to eliminate pops, clicks and other impulsive noise;
NoiseFree is designed to eliminate broad band noise.
What sets these two plug-ins apart from others is the quality of the
algorithms. In head-to-head comparisons with other digital audio restoration
software that I regularly use, the Agorithmix plug-ins produced consistently
superior sounding restorations.
For example, one of the problems that plagues almost all impulsive noise
filters is a tendency to modulate certain kinds of sound. The particular
conditions that evoke that problem can vary from plug-in to plug-in, but it
tends to rear its ugly head if you do enough restoration work.
After more than four months of using ScratchFree, I have yet to find that
problem. Instead, even when restoring recordings with very high levels of
pop and crackle, the resulting sound is clean and without the modulation
effect that can characterize so many other impulsive noise filters.
The graphical user interface (GUI) for both ScratchFree and NoiseFree
contains a window that displays a portion of the sound and the affect the
particular plug-in is having on it. In ScratchFree, the window is called the
“signal scope” and displays approximately 20 seconds of the signal in a
spectrum analyzer mode. In Noise Free the window is called the “Analyzer”
and the signal is represented in a typical time/amplitude mode with the
input signal displayed in red, the output signal displayed in green and the
noise profile displayed in white.
In each case, these windows are essential accessories that allow you to see
graphically and tangibly how the various adjustments are affecting the
program material. I find the graphical displays essential as I can see
precisely how the various parameters are affecting the sound.
Quiets Broad Band Noise:
Both GUI’s have a similar appearance with similar controls and that helps to
expedite the learning process. NoiseFree has three primary slider controls
on the left-hand side of the GUI: Threshold, Ratio and Ambience.
Based on my experience with other broad band noise reduction software, I
expected that the Threshold control would determine at what amplitude the
noise reduction would kick in and that the Ratio control would determine how
much noise would be removed. Under that scenario, you should be able to move
the Threshold control all the way up, and as long as the Ratio control is
all the way down, there should be no noise reduction.
That is not the way it works. This is part of what makes this software
different. While the Threshold and Ratio controls do interact, they don’t
interact in the usual way. Alogorithmix says that its Ratio control is
similar to an “expander ratio.”
In practice, raising only the Threshold control will remove noise. Moving
the Ratio control upwards will increase the noise reduction, but the higher
you raise it, the more it has the potential to adversely affect the sound
until you reach a point where the artifacts may become objectionable.
The third slider is called Ambience. As its name implies, it is designed to
preserve the ambience of the original sound. The higher that you raise this
slider, the more ambience is restored. Depending on the degree of noise and
the type of material, you may also add noise back into the output signal.
Removing broad band noise using NoiseFree requires a balancing act between
the Threshold, Ratio and Ambience controls. This may sound complicated, but
it isn’t. In fact, after a very short period of time, I found that adjusting
these controls was intuitive.
More to the point, the quality of the sound that I was hearing was superior
to anything that I could achieve using any of the several other broad band
noise reduction software that I regularly used. The sound that I was hearing
was more open with much more detail than anything that I had been able to
achieve in the past. To prove this, I ran several weeks of tests between the
older software and NoiseFree and consistently achieved a higher quality
sound from NoiseFree than I could from any of the several other broad band
noise reduction software that I had been using.
Creating The Noise Print:
NoiseFree provides three ways to create the traditional noise print that
determines what noise will be removed. As with most traditional noise
reduction software, you can create a “learned” noise print by selecting a
small portion from the sound file that contains just noise. For example, the
silent portion between cuts on a phonograph record.
You can also create a noise print from the sound itself. By clicking that
option, playing the sound file, and clicking “learn”, the software will
extract a noise print from the sound itself. The longer you allow for the
learn process, the more effective the derived noise print.
How well does this option work? That depends. I found that when I used a
sound file that contained just a person speaking, it was able to create a
noise print that was fairly close to what I could obtain by using the
traditional method of using a small portion of the sound file containing
only noise. In some cases the noise print was superior, as it was able to
find additional noise that might not be found by selecting an isolated
sample of noise.
With music, the derived noise print tended to be more complex than it would
have been if extracted from a small sample of noise. Because of this, at a
given setting of the noise reduction controls, the resulting noise reduction
could be a bit more aggressive than it would have been with a traditional
This can actually be an advantage on recordings where the broad band noise
is not constant since it enables the software to do a better job of noise
reduction. Even when the slightly more aggressive noise reduction wasn’t
desired, it could be tempered by simply backing off the noise controls a bit
to compensate for the more aggressive noise print. I found that in
situations involving only a moderate amount of broad band noise, the option
of creating the noise print from the sound itself was a real time saver.
In addition, there is a third way to create a noise profile. NoiseFree has a
button marked “EQ”. Alogrithmix calls this the “Noise Profile EQ”. When you
click on the EQ button, it opens an entirely new screen that represents the
noise profile in a five-band equalizer format.
This can be used to manually adjust the parameters of an existing noise
print that you have already created. Or by clicking on the “white” button,
you can create a straight-line representation of white noise. Starting with
this straight line and using the five band equalizer controls, you can
readily create a custom noise print of your own.
If you want to save a noise print, the Noise Profile EQ window is where you
will save it and/or recall other noise profiles that you have created. It
took me a while to get used to this as I would have expected to do this in
the main window.
Fine Tuning The Process:
NoiseFree also contains a row of five buttons that adapt the software
according to the type of material that you are working with. There are three
buttons for music and two for speech.
These adjust the resolution and some other internal parameters. While
Alogorithmix doesn’t spell out exactly how these parameters vary, judging by
the change in the appearance of the noise print and the sound, I would
expect that it is changing the FFT settings and possibly the degree of
For most purposes, I found that the Music 1 setting worked well. I did
experiment with the other settings but usually came back to that setting.
That probably reflects the similarity in the kinds of material that I work
NoiseFree also has what Alogrithmix calls “Expert Parameters.” The
Decorrelaton control can be used to help recover the transients that can be
lost when the noise reduction is run aggressively. Its affect on the
material is similar and complementary to the Ambience control.
The Response control affects the dynamic behavior of the de-noising process.
It appears to adjust the attack and release times of the algorithm. The
setting of this control, too, can help protect transients. At the same time,
it can also allow some noise to slip in and out between words.
The Chase control is an interesting parameter. When it is turned on, it
essentially monitors the ongoing signal and adjusts the noise print as it
perceives changes in the noise.
The higher you turn the control, the more rapidly it adjusts to the
perceived changes in the noise print. I say “perceived” noise changes,
because I am not altogether convinced that the algorithm is reading only
changes in the noise.
With music material, I found that the resulting noise print was generally
too aggressive and that it seemed to be based more on the music than on any
actual changes in the noise.
With speech, the Chase feature worked better. I believe that for forensic
applications where one is primarily concerned with intelligibility and some
artifacts are acceptable, the Chase feature could be very helpful.
Removing Pops And Clicks:
ScratchFree removes pops, clicks and scratches through a twofold process.
The DeClicker algorithm removes larger pops and clicks. It has a single
Threshold slider control. The higher you raise the Threshold control, the
more pops and clicks are removed.
The kinds of pops and clicks that are removed is determined by selecting one
of five buttons. The first two are designed to deal with the kinds of
impulsive noise found on vinyl records while the third button is optimized
for removing noise from 78 rpm records.
The fourth button is designed to remove noise created by digital sources and
button five is devoted to analog material that has experienced clipping due
to excessive levels.
In addition, ScratchFree has three Interpolation buttons that select
algorithms devoted to specific kinds of impulsive noise: A is for vinyl, B
is for digital and C is for 78 rpm material. Any or all of the Interpolation
settings can be selected and at any given time at least one will be in
For Experts Only:
Additionally ScratchFree has three “Expert” Parameters that fine-tune the
DeClicker part of the processing. “Width” affects how wide a click will be
affected. I found that the higher the Width control is set, the more likely
the DeClicker might produce artifacts at a given setting.
Essentially there is a trade off. If you need to remove very wide clicks,
then you may have to reduce the Threshold setting of the DeClicker to
prevent artifacts. Reducing the threshold setting may allow some smaller
clicks to sneak through the DeClicker. One way around this is to first
remove the wide clicks, and then rerun ScratchFree with the width parameter
set lower and the Threshold set higher to catch the remaining clicks that
slipped through the first time.
The second Expert Parameter is “Smooth.” In some applications, removing
impulsive noise can also adversely impact the brilliance of a recording. The
Smooth control is designed to adjust for this. It can help to restore lost
DePlop is the final Expert Parameter. It is designed to deal with subsonic
artifacts that can be created by the click removal process. Essentially the
control determines detection range of the DePlop algorithm.
What About Crackle?
To remove any remaining small clicks and crackles, ScratchFree has a second
process called DeCrackler. DeCrackler has two sliders: Detect and Remove.
Detect adjusts the width of the frequency range that will be affected by
DeCrackler and Remove determines the amount of crackles that will be
The higher you move each of the two sliders, the more crackle will be
reduced. Moving them too high can adversely affect the brilliance and/or
clarity of the material. Both NoiseFree and ScratchFree have a “Differ”
button that allows you to hear what each plug-in is removing.
I found that ScratchFree was able to remove as much noise as other similar
software that I regularly use, but it did so without creating the artifacts
that plague most impulsive noise reduction software. In my experience,
ScratchFree successfully removed large amounts of impulsive noise while
leaving the resulting sound clean and crisp.
Together, NoiseFree and ScratchFree provide a very high quality of digital
restoration. The software is easy to learn and apply and the user manuals
provide good explanation and documentation.
A Couple Of Caveats:
I do have some caveats. First, the software comes in two forms: DirectX and
VST. The DirectX uses a proprietary interface into which you can load up to
five different Algorithmix Pro-PlugIns. I found the PlugIn Center cumbersome
The PlugIn Center allows only one use of any particular plug-in, so you
cannot chain together two or more copies of ScratchFree, for example. With
some audio editors, I found that I could not successfully chain together two
or more copies of the PlugIn Center itself which would have allowed me to
effectively chain together multiple copies of the same plug-in.
The VST version works in the conventional manner. That is, each plug-in can
be separately loaded and used independently.
However, I found that when I used a third party VST wrapper to convert the
VST versions to DirectX to use with audio editors that don’t support VST, I
had some problems with ScratchFree.
With one audio editor, ScratchFree wouldn’t retain its settings when the
program was closed and reopened. In another, ScratchFree would crash the
program if I tried to chain two or more copies together.
These are relatively minor problems. Because of the extraordinarily high
quality sound produced by these plugins, I am more than willing to put up
with a slight inconvenience.
In summary, I personally have adopted Algorithmix’s NoiseFree and
ScratchFree for almost all of my digital audio restoration work. In most
cases the quality of restoration is superior to any other software that I
have used to date.
NoiseFree and ScratchFree are products of Algorithmix GmbH in Germany and
can be purchased in the U.S. for $1,999 each through Synthax, 5111 Market
St., Boardman, OH 44512. Voice: 330.259.0308 Fax: 330.259.0315 firstname.lastname@example.org.
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Category: Digital Audio Restoration DirectX/VST Plug-Ins
Price: $1,999 each
Plug-Ins provide an exceptionally high quality of sound restoration.
Each plug-in shares a common graphical user interface that is easy to
understand and use.
ScratchFree provides several different modes for removing vinyl, 78 rpm,
digital and clipping related impulsive noise’
NoiseFree can obtain a noise print from a noise sample or it can create a
noise print by analyzing the sound file.
NoiseFree’s Ambience and Decorrelation controls allow the restored sound to
retain a high level of detail.
Chase mode in NoiseFree adapts the noise print to changing noise conditions’
Plug-Ins can handle a variety of sample/bit rates up to 384 kHz (Tested to
96/24 by reviewer)’
Low CPU load enables real-time previewing and processing’
DirectX version requires use of proprietary “shell” that is a bit clunky to
The VST version of ScratchFree has some minor problems that don’t affect its
Read Burgan is a free lance writer and a former public radio station manager
specializing in digital audio restoration who can be reached at (906)
296-0652 or through e-mail at