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Dart Sharp At Noise Elimination:
A Software Review by Read G. Burgan
Published In RADIO WORLD March 19, 1997:

Digitally restoring old phonograph records requires at least two tools: 1. An impulsive noise filter to remove pops and clicks; and 2. A broadband nose removal filter to remove surface noise and other non-impulsive noise. Tracer Technologies was one of the first companies to produce an inexpensive PC based software for cleaning up old records with its DART (Digital Audio Restoration Technology). In its initial version, it had a pop and click filter. Now Tracer has introduced DartPro, adding a long needed broadband noise removal tool.

I was an unabashed fan of the original DART software. For my money, its DeClick is still one of the most effective PC based tools on the market. DartPro uses the same basic pop/click filter, but with an improved interface that is easier to use than the original. It includes a preview function, as does the new broadband noise reduction tool. Tracer gives you the option of setting the impulsive disturbance filter for either music or voice/music, giving you the flexibility to deal with most any kind of material. No pop and click filter will remove all pops and clicks; but DartPro will remove about as many as is humanly -- opps, digitally -- possible.

Regardless of whose digital noise reduction software I use, I often find myself coming back to DartPro to see if it will remove a few more pops and clicks without out disturbing the rest of the sound. It often does.

I also like the way that the DeClick gives you a report of the number of interventions after it completes the processing of a file. DartPro also allows you to compare the new and old files to see just how much -- if any -- of the actual sound file is being affected by your noise reduction efforts.

DartPro actually gives you two options for reducing broadband noise: 1. DeNoise and 2. DeHiss. If you're in a hurry, DeHiss may be all that you need. DeHiss is based on a standard noise model developed by Tracer to deal with the kinds of noise associated with vinyl and tape. Both DeHiss and DeNoise allow you to adjust several factors affecting the noise reduction, including Gain/Weight, Smoothing Range, Frequency Carving, Frame Size and Overlay.

The difference between DeHiss and DeNoise is that DeNoise allows you to sample a noisy portion of your sound file and create your own custom sample that DartPro will then use to remove the noise. This takes a little time and if you want to really be sure that the noise you have is representative of the whole album you may need to take several samples and test each against a section of the record.

Theoretically DeNoise should give you a better result since it is an actual sample of real noise in your sound file. However, vinyl noise is a bit tricky, and there are times when I found that the DeHiss actually seemed to do a slightly better job than DeNoise. This is because Tracer has designed the DeHiss tool to effectively model the kinds of random noise that can characterize a vinyl recording.

The bottom line is that either of these broadband noise reduction tools will effectively remove much -- and in many cases -- all of the noise associated with vinyl and other kinds of files. Typically, I found that DeNoise removed at least 30 dB of noise in its "normal" setting. Setting the tool more aggressively can remove more noise, but at some point you will begin to affect the quality of the sound file. DeNoise and DeHiss work well, and are easy to use.

DartPro also contains a number of other digital audio processing tools including lowpass, highpass, bandstop, bandpass and notch filters and a nine band graphic equalizer. These tools are all easy to use; some are fairly rudimentary in design and could use some additional features. The notch filter, for example, does not allow you to adjust the depth of the notch cut. The BandStop filter gives you only three choices of attenuation, 20, 40 or 80 dB.

However, each of these tools works, and together they provide enough flexibility to clean up and equalize almost any sound file. There are also functions that allow you to fade in and out and crossfade.

Tracer has also include a spectrum analysis screen in DartPro. I find the ability to apply spectrum analysis to a sound file an indispensable aid in determining what tools to apply and then testing how well the particular tool has worked. DartPro's Spectrum Analysis screen does not provide enough useful information to be of much help.

It does not annotate either the dB range or the frequency components of the signal being analyzed. Including a spectrum analysis function is a step in the right direction, but this one needs a bit more improvement before it becomes really useful.

There are also a few other items on my DartPro wish list for their next version. One would be the ability of the screen to scroll when playing a sound file. Another would be a true "undue" function. The program comes with a default limit of 40,000 bytes. While this can be changed, the bottom line is that if you don't like an edit you've made, you may well have to scrap all of your work to that point and start over. Finally, I'd like to see a "Preview Cut" function that would allow you to hear what the sound file will sound like when you manually cut a pop or click that the filter wasn't able to remove.

The bottom line is that DartPro is an effective way to remove both impulsive and broadband noise from vinyl and other recordings. It works well and is easy to use.

DartPro can be purchased direct from Tracer Technologies for $399. It requires an IBM compatible PC with at least a 486DX processor, Windows, a sound card and a hard drive large enough to handle the kinds of sound files you will be using.

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Tracer Technologies Inc., 1600 Pennsylvania, Suite 101, York, PA 17404 (717)-843-5833; (717)-843-2264 Fax.

Read Burgan is a free lance writer and a former public radio station manager who can be reached at (906) 296-0652 or through e-mail at rgb@up.net.