DART

Digital Audio Restoration Technology (DART)
by
Read G. Burgan

Until now, if you wanted to remove the pops, clicks and related noise on your vinyl long play records, you had only a couple of choices. You could use hardware based processors like the Burwein/KLH Transient Noise Eliminator (If you can find one!), or MAC based software like that produced by Digi Designs or Sonic Solutions where you could easily spend $10,000 to $25,000 or more. Until now.

Tracer Technologies, Inc. of Dallastown, PA has introduced a new PC based software designed to eliminate the noise associated with analog based recordings -- at a fraction of the price normally associated with digital noise reduction software.

The software, Digital Audio Restoration Technology (DART) is actually a crossover product: It's designed to appeal to both the professional and the consumer markets. On the consumer side, the program is inexpensive, runs on the ubiquitous PC and is very easy to run. In fact, if you're willing to accept the default processing values, you can begin processing as soon as the program is installed on your computer.

But don't let it's inexpensive price and its ease of operation fool you. This is a professional product. If you're willing to take the time to become adept with all of its many features, you'll find all the tools necessary to clean up a truly noisy recording. DART is a very powerful program.

DART was created in Poland by a team of scientists located in GDansk. It's marketed in this country by a new company called Tracer Technologies Inc. that is made up of former sales and marketing people from Turtle Beach. According to Jeff Klinedinst, Tracer Technologies is dedicated "to bringing innovative and new products to a worldwide market and to giving them a chance for access to channels usually only available to large and wealthy companies."

How well does their first product work? What does it take to run it? How much does it cost? Tracer Technologies is still lining up dealers for its product, but you can purchase it direct from them for $299.

DART requires a minimum of a 486 computer with Windows 3.1, a 16-bit sound card and a large hard drive. How large a hard drive? A stereo soundfile recorded at a sampling rate of 44 kilobytes can require up to 11 megabytes per minute. In addition, when DART processes your soundfile, it will make at least one duplicate of it.

I installed DART on a 486 DX-50 (Not a clock doubled machine) with 16 meg of ram, a Turtle Beach Monterey sound card and a 1 gigabyte SCSI hard drive that was already dedicated to digital audio files. I had no trouble installing DART and it's two disks only used about a meg and a half of space on my hard drive -- a pleasant experience considering most Windows programs hog 20 megabytes or more.

At first I had a lot of trouble getting DART to work properly. When the audio wasn't stuttering, the program was crashing. As it turned out, the fault was mine. DART requires Smartdrive to be operational on the hard drive containing the soundfiles. I also use Innovative Quality Software's Software Audio Workshop (SAW) which suggests that you turn Smartdrive off. Once I edited my autoexec.bat file to turn Smartdrive back on, the problems cleared up and DART began to perform flawlessly -- almost.

Recording is straightforward. Clicking on the record menu gives you a screen with controls that emulate a cassette recorder (Rewind, Stop, Fastforward, Play, Record and Pause). In addition it has the equivalent of a bar graph representing the left and right recording signals in decibels. Recording in DART is as easy as recording on an analog cassette machine.

When you've finished recording, DART will ask if you want to "register" the recording. This means it wants to make a working copy. Each time it processes a soundfile, it will continue to create more working copies. The good news is that if you don't like the results of a particular processing session, you can always go back to the previous soundfile. The bad news is that it doesn't take much time before these soundfiles have eaten up a large portion of your hard drive. You can tell Dart to make its processing changes to one of your existing files, but if you don't like the results, you'll lose all of the other changes on that soundfile as well. DART keeps detailed information on the particular processing changes it makes to a soundfile, including the number of interventions and the particular settings for the noise reduction components. You can access this information at any time by clicking on the information icon. I found this a particularly useful feature after I had made a half dozen different processing attempts and could no longer remember exactly what I had done to each soundfile.

DART uses three tools to remove analog noise. For those working with phonograph records, the most important is the outlier which detects and removes impulsive disturbances, i.e.: pops, clicks and crackling noise. The outlier works much like the original hardware based transient noise reducing units. When it finds an impulsive noise, it removes it and replaces it with a sample of sound taken from an area immediately adjacent to the noise.

How well does it work? To test the unit, I recorded a short portion from a 1935 sixteen inch broadcast transcription of a radio program. The program had plenty of noise. I then made several test recordings. The first was with no noise reduction applied at all. The second utilized my KLH transient noise suppressor and dynamic noise filter. Finally I created a soundfile consisting of the same material as processed through DART using its default settings in Easy Run.

While DART did not remove all of the associated noise, it beat the hardware based noise processor hands down and produced a recording that was indeed significantly quieter than the original. It's important to note that DART has two overall settings for its outlier processor: Music and Music and Speech. Because the human voice is capable of producing bursts of energy that mimic impulsive noise disturbances, DART provides the second setting to take this factor into account. Since I was processing program material with speech, I used that setting. By its very nature, this setting is less aggressive than the music setting and will leave more noise.

But DART offers options that include locating specific blocks in the soundfile for re-processing. When I zoomed in on the soundfile I could easily recognize the larger impulsive noise areas. By limiting the action of the outlier to a small block, I could reset it to the more aggressive music mode and readily eliminate the remaining disturbances without adversely affecting the program material. While it takes some time to do this, the result is a very quiet recording.

The outlier's detection threshold can be set from a range that extends from 3.0 to 10.0. If the range is set too low, it can become too sensitive and eliminate actual program material. If it's set too high, it can become too insensitive and miss small noise disturbances. By adjusting the threshold setting, you can experiment with different settings and find the one that's appropriate for the noise and material on the particular audio source you're processing. You can also re-run the outlier on previously processed material, either using a new setting or just maintaining the original setting. This is the equivalent of running the material through a series of cascading filters.

In addition, DART creates a separate digital binary file every time it processes a soundfile. This file contains markings for all of the interventions the software has made in your soundfile. If you think it's missed an area, or has targeted an area that isn't really noise, you can edit the detection file to reflect this. Then you can select the re-run option which will re-process the soundfile using your corrected digital binary file as the basis for its noise reduction.

If you like, DART will create a Comparison file in which it will subtract the processed soundfile from the original. This creates a file that contains all of the impulsive noise that it has removed from the original soundfile. Why would you want such a file? This gives you an opportunity to hear firsthand what DART has removed. If it selected any program material, you'll hear it here.

In many cases, the Outlier may be all you need. But DART has two other noise reduction/restoration components. The Smoothing Factor is "a special adaptive version of a device known as the Kalman filter." (Quote form the DART manual) It can be set in a range of 0.0 to 2.0. Tracer recommends that it be used during the first pass with the outlier.

DART also includes a Postfiltering Factor deigned to deal with wide-band noise including tape hiss and record surface noise. It is particularly designed to suppress noise in the quieter portions of the recording without affecting the louder portions. Its range is adjustable from 0.0 to 2.0.

When I received DART, I was working on a project to transfer 1950's vintage piano solo recordings to a digital format. Using DART, I was able to remove about 95 percent of the pops, clicks and associated noise. In regions of the soundfile where the music was loudest, the program let a few large pops sneak through. This is understandable for two reasons: First, the very nature of the material -- piano music -- provides content that is itself impulsive and therefore mimics the very impulsive noise that the software is designed to remove.

Secondly, the program material was so loud that it effectively masked the noise. While the human ear could hear it, the software could not.

I found it easier to finish the noise reduction using Innovative Quality Software's SAW, in part because I've been using it for several months, and in part because I find it easier to move around in SAW. Using SAW, I simply marked both sides of any remaining noise disturbances and cut them out.

After working with DART for a short time, I did find some problems. For example, at the top of the screen DART displays a long narrow window called the Overview which is designed to represent the entire sound file. To move around in the soundfile, you simply click on a portion of the Overview and press play. At least, that's the way it's supposed to work. In reality, if your soundfile is much longer than three minutes, the cursor will not click on any portion other than the beginning of the soundfile. To move around in a soundfile, you have to click on a soundfile window, which contains only a few seconds of a soundfile. You can then move around by clicking on the ribbon beneath the soundfile window. Unfortunately, since you can only see a few seconds of the soundfile at any moment, it's extremely tedious to locate a particular portion of a long soundfile. Tracer is now aware of this problem and its programmers are seeking a solution.

In addition, even when the cursor works in the Overview section (on a file three minutes or less), when you press stop, the cursor returns to its original starting position. I find this extremely irritating when I've just located a noisy area several minutes into the soundfile that I'd like to mark and process. What I need is for the cursor to stop right where it is when I press the stop function so that the spot will then be represented on the zoomed-in portion in the soundfile window. Instead I have to try to relocate that exact spot and it can take a number of attempts. Tracer has not indicated if it intends to add an option that will allow the cursor to remain where it is when you stop playing the soundfile. I hope they do.

DART contains other useful tools including Scale, Maximize, Mute, Reverse and filtering including Lowpass, Highpass, Bandpass and Notch filtering. Scale and Maximize allow you to adjust the level of the signal, Mute erases a portion of the signal and Reverse allows you to run the soundfile (or a portion) backwards. Backwards? Yes, backwards. Why? Sometimes the nature of the recorded material is such that the outlier can more readily distinguish between the impulsive noise and the program material by processing it in reverse. Actually, it's a nice touch. Just don't forget to reverse the material after you're done!

The filters work pretty much as their hardware equivalents. The Lowpass filter removes high frequency material while allowing the low frequency material to pass through. The High pass filter removes the low frequency material while allowing the highs to pass through. The band pass filter allows you to affect both the high and low frequency areas simultaneously. In effect, these three filters provide a shelving function which lets you pick a frequency(ies) and set the amount of attenuation per octave. The Notch filter lets you remove frequencies from a very narrow frequency -- 60 cycle noise being the most common example. While you can set the frequency of the notch and its depth, you can't set its width.

DART also contains a graphic equalizer with 8 bands. While adequate, it's essentially a device for attenuating frequencies. It would be helpful if the equalizer operated like its hardware equivalent, with a standard center position allowing you to boost or attenuate frequencies as necessary.

Some caveats. DART is not the answer to all of your noise reduction and elimination needs. No product is, not even a digital one. Consider it one more tool in your arsenal of weapons to eradicate noise and improve your audio product. I'm not about to give up my Aphex 250 Aural Exciter or my Alesis Quadraverb Plus, even if they are analog devices.

Neither is DART a silver bullet. If you're looking for a program where all you have to do is push a button and all of your noise will be magically eradicated, keep looking. But if you're willing to take the time to master all of DART's tools and spend a significant amount of time in applying them, you can turn a very noisy soundfile into an acceptably quiet one.

DART still has some bugs to work out. Every time I attempted to use the Easy/Run/Block option, the program crashed. It crashes once in a while in other modes. But DART is still in its first version, and most new software has bugs that only get discovered and eliminated after its been out in the real world for a while.

If you want to do full scale digital audio production, you'll need more than DART can offer. The ability to fade, cross fade, multi-track mixing, etc. A good all around starting digital package would include Tracer Technologies DART and Innovative Quality Software's SAW and SAW Utilities package. For a total street price of under $1,000, you can have digital audio tools that until now would have cost you $10,000 to $20,000. Digital Audio is no longer only an option for well heeled radio stations and production facilities.

In the end, DART is an amazing product. It's fast. While its actual operating speed will depend on the computer it's running on, I found that it took an average of slightly more than 5 times the length of the soundfile it was processing. Many of the more costlier software systems take much longer. Will it remove every vestige of noise in your worst analog recordings? Probably not. Nor is it likely that any other product will. For its modest price, it provides incredibly effective tools for reducing nearly all of the noise associated with phonograph records and other analog recordings. It's easy to use and it does what it claims. If you want to remove the noise from your analog recordings you're not likely to find a better product at a price that even approaches DART.

-- The End --

For further information:
DART: Tracer Technologies, Inc., PO Box 188, Dallastown, PA 17313 (717) 747-0200 or e-mail at 102037.2437@compuserve.com.

SAW: Innovative Quality Software, 2955 E. Russell Rd, Las Vegas, Nevada, 89120 (702) 435-9077

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 AH746@detroit.freenet.org.