Whether you do your recording in a professional environment or a home-based studio, noise can be a problem. The source of the trouble can be tape hiss, clicks and pops from bad cables, low-frequency room rumble, ground-loop buzz, or other common culprits. By taking some precautions, you can prevent most noises, but when some still make it into your masterpieces, Diamond Cut Audio Restoration Tools 32 (DC-ART 32) may be the cure you need.
Originally designed for restoring old phonograph recordings, DC-ART 32 (created by Diamond Cut Productions and published by Tracer Technologies) has evolved into a professional application that can remove most types of noise from just about any audio material. The program provides a variety of sophisticated filtering algorithms that include Impulse Noise, Continuous Noise, and Dynamic Noise filters. There are also Harmonic Reject, Median, and Average filters, along with a wide range of equalization and dynamics-processing tools.
I installed DC-ART 32 on a 300 MHz Pentium II and tested the program with a number of audio recordings. I successfully removed hiss from some of my old analog tapes and cleaned up the clicks and crackles from various albums and 45s. But even though the results I got were excellent, actually working with the program was a bit of a chore.
HOW IT HANDLESWhen you open a file in DC-ART 32, it is displayed in a window with two panes. The source waveform is shown on top and the "destination" on the bottom (see Fig. 1). The panes can be synchronized so that if you scroll in one, the other follows. (Synchronization doesn't apply to zooming, though.) Despite appearances, you can have more than one source/destination file set open simultaneously, each with its own window. Unfortunately, when you close DC-ART 32, it doesn't remember which files you had open or the various settings (such as window position) that you applied to them.
When you process a file, DC-ART 32 reads the data from the source waveform, applies the filter, and then displays the result as the destination waveform. At that point, you can apply additional filtering to the destination waveform in case you have more than one type of noise to deal with. Initially, this seems like a great way to work. Your source file stays untouched, and you can see, hear, and compare the results easily. The problem is that any subsequent processing to the destination waveform can't be undone. The Undo command in DC-ART 32 works only with basic functions such as cut, copy, and paste. And if you select and process the source waveform again, your previous destination waveform results are overwritten.
To manipulate the results of a previous filter process and still have the option to undo your actions, you have to use the Make Destination the Source function. This simply copies the destination waveform from your current window to the source waveform of a new window. After running a few filter processes, your workspace becomes cluttered with a lot of windows, which is especially cumbersome because you can't name the windows unless you save them to disk.
DC-ART 32 does provide some features that make its operation a bit easier. "Nonmodal" dialog boxes let you keep one filter's dialog box open while you access another filter dialog. You can also apply any of the program's other functions while any number of dialog boxes are open. This can be a real time-saver, but you have to use this feature judiciously: too many open dialog boxes just add to the aforementioned clutter.
To help streamline processing tasks, DC-ART 32 lets you store presets for any of its filter functions, including all the noise-removal and equalization filters. The program also has a wide variety of default presets that cover typical analog-tape and phonograph noise prints, European and American buzz filters, vintage radio equalization curves, and more. One addition I'd like to see is the ability to string several presets together for quick batch processing.
DC-ART 32's absence of keyboard shortcuts will likely displease most power users. The program provides only a few shortcuts covering basic functions such as opening a file and copying, cutting, and pasting data. There's no way to add or customize your own shortcuts. Most functions must be accessed with the mouse or with multiple key combinations (such as pressing the Alt key, then the first letter of the menu you want to access, and then the first letter of the function you need).
FILTERS FOR ALLDC-ART 32 provides a nice set of filters for dealing with many types of audio disturbances. Impulsive noises, such as pops, ticks, and clicks, are handled by the Impulse Noise filter. It scans an audio file for sharp spikes in the waveform and replaces them with an approximation of what the signal might have contained during that brief occurrence. You can set the Threshold (the signal level that a spike has to surpass in order to be identified and removed), the Size (the minimum number of audio samples a spike has to occupy before it's removed), and Tracking (a parameter that determines how well the program distinguishes between spikes and percussive musical content). During my tests, I was able to remove all of the impulse noises from my LPs without any audible side effects. That was very impressive.
Continuous noises such as tape hiss, low-frequency rumble, hum and buzz, and other sustained background disturbances are dealt with by the Continuous Noise filter, the Dynamic Noise filter, or the Harmonic Reject filter. Each has its strengths and weaknesses. The Continuous Noise filter is the most effective of the three, but it's also the most difficult to use. You begin by highlighting a part of the audio waveform that contains only the noise you're trying to remove. Then you click on the Sample Noise button, and DC-ART 32 displays the frequency spectrum of the sample (see Fig. 2). The red line in the graph represents the frequency spectrum of the noise, and the blue line represents the threshold.
You can adjust the entire threshold using the Shift and Threshold buttons, or change the threshold for only part of the spectrum by dragging the dots up or down along the blue line. DC-ART 32 breaks up the spectrum into 1,000 separate bands. Each dot represents 100 of those bands, and you can change the center frequency of each dot by dragging it left or right. You can't add more points along the threshold for more accurate adjustments, but even so, the filter performs quite nicely. As you fine-tune the threshold, you can have the program play a continuous preview of the file. You can also listen to the part of the signal that's being removed by selecting the Keep Residue function.
It takes quite a bit of trial and error to get the Continuous Noise filter just right so that it doesn't cut out an important part of the signal or introduce unwanted artifacts. Most of the time, the filter does its job very well, but if all you need to do is remove some high-frequency hiss, the Dynamic Noise filter might be a better choice. This filter works on the same principle as basic analog single-ended noise reduction. It provides a movable lowpass filter that attenuates high frequencies only when there is no high-frequency music content present in the signal.
The Harmonic Reject filter (more commonly known as a "comb" or "multiple notch" filter) lets you eliminate noises that are centered around a certain frequency, such as 60 Hz ground-loop hum or harmonically rich buzzing caused by radio frequency interference. You can adjust the fundamental filter frequency from 5 Hz to 5 kHz and the attenuation from 0 to 100 dB. For buzzing noises, you can choose to filter odd or even harmonics and set the number of harmonics from 1 to 500.
DC-ART 32 also provides Median and Average filters. According to the manual, these filters have no analog equivalent. You simply set a number of samples (3 to 20 for Median and 2 to 100 for Average), and then let the filter do its thing. These filters work by taking the median or average values from the source waveform, within the sample window you defined, and passing those values to the destination waveform. I found these filters to be particularly effective in reducing the crackles on my LPs.
EQ AND DYNAMICSIn addition to its special noise filters, DC-ART 32 provides a wide range of equalization and dynamics-processing tools. Its arsenal includes lowpass, bandpass, highpass, and notch filters. Each provides the usual frequency parameter along with a filter slope that can be set to 6, 12, or 18 dB/octave. Of course, instead of filter slope, the notch filter has a bandwidth parameter that can be set from 0.01 to 1.99 octaves. A basic 10-band graphic EQ with a +/-12 dB range for each band is also provided, along with a paragraphic equalizer (see Fig. 3).
I found these to be quite powerful tools-more powerful than the same functions found in other professional software, because you can define up to ten filters, each with separate frequency, amplitude, and bandwidth settings. What's more, you can adjust each filter by typing in values or simply dragging points along a graph. This allows you to create some extremely impressive equalization curves.
The Dynamics Processor is not quite as useful. It provides basic compression, expander/gate, and de-esser functions. You can set the threshold, ratio, attack, and release for the compressor and set the threshold and ratio for the expander/gate. The de-esser can only be activated or deactivated; it has no frequency or bandwidth controls.
OTHER TOOLSTo correct speed variations in analog-tape and vinyl recordings, DC-ART 32 has a Change Speed function that lets you vary the pitch/speed of audio over time. What's especially cool about this feature is that you can define the changes graphically by dragging points to create a curve (see Fig. 4). The Gain Change function operates in a similar manner and allows you to define linear, logarithmic, or curved gain slopes over the course of a recording.
DC-ART 32 also has reverb and Virtual Valve Amplifier effects. The reverb provides only basic room-size, reflections, decay, and early-level settings. It sounds quite good, but it can't compare to dedicated reverb plug-ins. The Virtual Valve Amplifier, on the other hand, is very cool. It provides drive, operating-point, detail, and mix parameters along with a Spectrum setting. You can even define the tube type/configuration for Triode (12AX7, 12AT7, or 12AU7), Pentode (6EJ7), 2-Stage Class A, 2-Stage Class AB, Exciter, and Transformer Class AB. My only gripe with DC-ART 32 as an effects tool is that there is no DirectX support. The internal effects are a nice addition, but I'd much rather be able to use my own plug-ins with the program.
Finally, DC-ART 32 has some other useful basic functions like Reverse File, Markers, Crossfade, Make Waves (a test-signal generator), and Gain Normalize. There's also a CD-Prep menu with functions that help you find and mark silent passages automatically and break files into smaller chunks in preparation for CD burning. It provides no actual CD-burning functions, though.
FINAL PROCESSDC-ART 32 can be cumbersome to use, to say the least. Among the major annoyances: the program supports only the WAV file format, Undo doesn't function in the standard manner, and you have to open a new waveform window for each filter process. Luckily, the program comes with a very helpful demonstration file and excellent documentation; the manual is one of the best I've seen. Not only does it include information about all the features of the program, but there's also a tutorial for every feature. If you follow these instructions, DC-ART 32's esoteric working procedures won't get in the way as much.
Even though DirectX support is lacking, DC-ART 32 is an excellent set of tools for dealing with a wide variety of audio blemishes. Most of the tools provide a good range of parameters, and the output quality is very professional. Furthermore, at $199 the program is one of the least expensive in its category. For all the power it provides, I have to say that DC-ART 32 would be a valuable asset to any audio engineer.