Bias Sound Soap Pro

What Is It?

SoundSoap Pro is a restoration utility designed to remove various kinds of sonic "dirt" from recordings, including rumble, hum, clicks, crackle, broadband noise, and general background noise. It operates as a plug-in with host applications under Mac OS 10.2 and above (RTAS, VST, AudioSuite, Audio Units) or Windows XP (RTAS, DirectX, AudioSuite, VST). Operates on all file formats supported by the host application (AIFF, WAV, etc. up to 32-bit, 192 kHz).

User Interface

SoundSoap Pro consists of four DSP components, each of which can be independently activated. These modules are arranged in a chain from left to right in the recommended processing order: Hum & Rumble, Click & Crackle, Broadband, and Noise Gate. The user interface is clean and uncluttered, with the main central pane switchable between either a brief help text or the control and display panel of one of the four modules, each with a spectrogram display at the top. At the bottom of the window is a set of tabs containing thumbnail views for these panels, so the principal parameters of all four are always visible in miniature while one or another module is selected for tweaking. Click on a tab to open one of the control panels in the programming pane. Most parameters can be adjusted either by dragging a graphic fader or by direct numeric entry.

Recommended procedure is to first reduce any continuous low-frequency noise (rumble and hum), then high frequency transients (clicks and crackle), and then to address the more difficult task of broadband noise reduction. Finally the noise gate can be used to clean up any remaining traces of grit in the silences. Two global controls are always available to help you audition your work as you go: 1) The A/B/C/D Compare buttons give you four snapshots of your processing settings for comparison as you zero in on your finished version. 2) The Noise Only button allows you to hear only what is being removed from the recording. This is absolutely critical since many of the noise components you may want to eradicate may inhabit the same spectral region as the program material you want to keep. There will be a degree of tradeoff in your final choice of noise reduction settings and this option lets you rescue important elements before you toss them out in a fit of cleanliness.

Here are the individual modules:

Spectrogram Display
SoundSoap Pro features a spectrogram (a.k.a. spectrograph or sonogram) display, which plots frequency against time and uses color saturation to represent amplitude. It shows input signal in white (against black) and output signal in red, so you can tell at a glance which portion of the spectrum is being removed by the noise reduction algorithms. Therefore with none of the modules engaged the sonogram is red against black, but as you use the various algorithms to "carve away" noise elements you will see patches of white or gray where parts of the input spectrum didn't make it through (this is particularly easy to see if you engage the Rumble filter and turn the cutoff frequency up to 500 Hz).

Hum & Rumble
This is a set of filters optimized for cutting low frequencies, such as turntable and air conditioner rumble and the hum from AC ground loops. The Rumble section is a simple high-pass filter with a slope of 12dB, a Q value of 0.5, and a frequency range from 20 to 500 Hz. Rumble can be engaged separately from the Hum section, which consists of a set of nine harmonically-related notch filters with parameter controls for Frequency (20 to 196 Hz), Q (2 to 50), and Depth (0 to 120 dB). The number of harmonics can be selected, so you can target just the fundamental or broaden your response to include up to eight overtones (e.g. 60 Hz plus 120, 180Š up to 540 Hz). A Tilt parameter (with a range of 0.0 to 1.0) allows you to adjust the balance between higher and lower harmonics. For instance, a value of 0.5 would cut the fundamental by the Depth parameter value and then would cut the second harmonic by 1/2 of that amount, the third harmonic by 1/4, the fourth by 1/8, etc.

Click & Crackle
This module is dedicated to removing transient sounds such as vinyl surface noise and electrostatic signal contamination. There is a single Click Meter, which blinks red when a click is detected, and just two adjustable parameters: Click Threshold (1.0 to 25.0) and Crackle Threshold (10.0 to 16.0). Lower parameter values result in the removal of more transient artifacts since they cause the detection algorithm to respond at lower amplitude levels.

Broadband
This is the most elaborate of the four processors, and can have the most profound affect on the overall quality of sound. It is also the one that has the greatest potential to do more harm than good, so it must be used with care and understanding, and above all with careful listening. The user interface is built around a 12-channel combined spectrum meter and graphic equalizer with separate slider controls for Threshold (0 to 70 dB) and Reduction (0 to 40 dB) amount for each channel. There are also global Attack and Release parameters (5 to 150 msec), each with its own Tilt adjustment to regulate the time response between lower and higher frequency bands.

The recommend method for broadband noise reduction is to use SoundSoap's "Learn Noise" mode, which requires that the sound file contain a short passage possessing the characteristic unwanted noise but none of the desired musical program material. While the noise passage is playing, click the Learn Noise button; SoundSoap will capture the spectral profile of the noise and will subsequently remove it from the recording. This is where you need to be careful, since any musical material you might capture by mistake will also be removed from the recording. For this reason it is best not to trim the head and tail of your recording until after performing the noise reduction, in order to give yourself ample noise "ambience" to sample.

Here's the working procedure: The spectral analysis display will show a nice green spectral envelope jiggling along while the music plays. When you click Learn Noise the 12 blue slider knobs of the Threshold parameter will snap to the current signal levels for their channels. You can then adjust the yellow Reduction slider knobs to control the amount of noise you want to remove. You can also drag the captured Threshold values up and down as a group. By default both of these groups of 12 values are locked together, but it is possible to unlock them in order to adjust individual spectral bands. In this way you can apply noise reduction to just that part of the spectrum where it is critical while turning it off or diminishing its effect where it seems to "rob" the musical signal of depth, character, or brightness. As always it is important to monitor your work in Noise Only mode so you can be aware of how much baby you may be throwing out with the bathwater.

Noise Gate
Being exactly what its name implies, Noise Gate is probably the most familiar of SoundSoap Pro's modules. Parameters include Threshold (-60 to 0 dB), Reduction ratio (1.0 to 5.0), Attack (10 to 500 msec), and Release (50 to 1000 msec). In addition to the global spectrogram display, it has its own waveform display, with Left, Right, and Left+Right view options, that makes it easy to set the Threshold parameter visually as well as aurally. Note that noise gates are the quickest and easiest way to achieve a semblance of noise reduction (because the quiet passages can be made dead silent with little effort) but you run the risk of abruptly truncating sounds that delicately fade in and out. Better you should perform all the other reduction techniques first and then resort to the noise gate (if really needed) to clean up the last stray bits of sonic flotsam.

In Use

I've tried SoundSoap Pro on a variety of material including old classical music LPs, live recordings of my '60s psychedelic band, ancient recordings of famous poets reading their work, and a variety of musical and sound effects material that was ostensibly undamaged but which gave me somewhat of a benchmark to help understand the various noise reduction algorithms.

By far the most straightforward and effective job was done on the vinyl LPs. Though I had no serious hum and rumble problems (and these were readily corrected with Hum & Rumble) there was surface noise aplenty. Following the recommended procedure I invoked the Noise Only monitoring mode and moved the Click Threshold slider through its range. As you'd expect, the lower the threshold the more clicks and pops were being excised. However, this was not entirely a good thing. When I switched back to normal monitoring mode I could hear the holes that were being punched in the music by the deletion of the clicks. When I returned to Noise Only mode I listened carefully to the clicks and quickly became aware that a certain "pitchiness" was an indication that snippets of music were being identified as noise clicks. By raising the threshold from the minimum of 1 to about 3 (out of 25) I could "tune" the algorithm to cut out just those clicks that had a more noise-like character. I followed a similar strategy with Crackle Threshold (arriving at a setting of 11 out of 16) and was much more satisfied with the results.

This Noise Only monitoring strategy proves also to work well with the Broadband algorithm, though with a level of difficulty that is orders of magnitude greater. Unlike clicks, which are well-defined transient events, broadband noise overlaps the program material to a great degree and baby/bathwater problem is almost always present. The greatest success will be achieved if you have a good isolated sample of the noise and if that noise is relatively unvarying throughout the whole recording. It is also critical that the "noise" be truly "noisy" in the sense that it be random. Unless you have a fully-isolated sample for analysis, feedback or a continuous buzz are impossible to eliminate with SoundSoap's tools because they are coherent (rather than noise-like) and because they are similar to other sounds that are part of the desired music. Another problem area that seems to be beyond SoundSoap's capabilities is the demodulation of various types of distortion such as microphone overload. To perform such a fine level of sonic surgery you'd need different set of tools, including specialized hardware such as Cedar or Sonic Solutions, at a drastically higher price. I haven't seen a software-only solution on the Macintosh that can beat SoundSoap Pro for ease of use and sonic results (I've previously used both Prosoniq SonicWORX and Waves RestorationX).

But for garden variety noise the Broadband tool is excellent. As described above, in most cases the first step is to capture a sample of offending noise and to analyze its profile. This is done by clicking once on the "Learn Noise" (it grabs about 0.1 second) or by clicking twice on its companion clock button (to grab a longer sample if it's available). If all you have is a tiny window of noise you can cheat a bit by setting loop playback in your host application. The analysis will be performed automatically and the Threshold values will be set for you.

I found it is best to do a little ear training first by selecting some test files. I have some noisy sound effects files, some voice files, and an assortment of music clips that offer a wide range of noisy and pitchy sounds. I found it especially instructive to explore a sound called "airplane interior" in order to hear what SoundSoap does with nearly pure noise. By varying the Threshold and Reduction settings I was able to induce a pitchy quality in the noise source (this suggests that SoundSoap's algorithm is actually "killing" uncorrelated noise elements while reinforcing correlated pitchy components) but whether or not your are a DSP math wonk you'll be able to hear what's going on and establish some intuition about how to apply these tools to your particular projects.

Installation, Documentation, And Support

Installation from the CD is easy and is well documented in the manual. The Authorization scheme is based on a combination of a hardware dongle (the BIAS Key), entry of your Serial Number, and on-line registration (you can delay the registration for up to 14-days). Frankly, this multiple-layered protection scheme seems a bit excessive, but I won't complain too much, BIAS has to protect its substantial investment in development in order to bring us these tools.

The 76-page manual is included in both printed form and as a PDF file. It is clearly written and fully illustrated, and it contains an extensive Tutorial section that addresses several different noise reduction situations.

BIAS Support has always been good, but as with other growing companies they've had to accommodate to the support needs of an increasingly large customer base. As a result there are limits on free technical assistance (90 days for up to three incidents). After this you'll have a choice of a fee-based system with phone support, or an Internet-based system with FAQ, forum, and mailing list available free. Personally, I think the mailing list is one of the best support systems I've seen. It's active, with five to ten message a day, of which several are typically from a BIAS company representative fielding questions and providing rapid response to user problems.

Summary

SoundSoap Pro is a noise reduction utility that does a creditable job in repairing many of the more common problems with old and damaged recordings (such as vinyl records) or poorly recorded material (where hum or excessive background noise are present). It has a modular architecture, with each type of noise reduction task in its own window, and it provides a nice balance of manual and automated parameter adjustment. For those lacking the budget for a high-end dedicated system this is a respectable solution.

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