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Plug-in Cuts Hash With Noise Gate:
A Software Review by Read G. Burgan
Published In RADIO WORLD March 30, 2005:

Read G. Burgan
Software Review

Most digital noise reduction software use similar approaches. While there are differences in the details, at their heart are impulsive and broadband noise removal tools.

Bias Inc. has released a new noise reduction plug-in available for Mac and Windows XP hosts utilizing DirectX, RTAS and VST plug-in’s that manages to move the classic approach to a new plateau. The first difference is in the design of the plug-in itself.

One For all -- All In One

In the past, each noise reduction tool had its own particular plug-in. Bias has created one noise reduction plug-in that includes four noise reduction tools in modules that it calls “Tabs.”.

There is a method to the Bias approach. Noise reduction works best if the tools are applied in a particular order. By design, Bias’ plug-in applies the tools in the recommended order.

The plug-in works in a manner similar to the chain feature that many digital audio editors provide allowing you to chain together a number of tools and then apply and hear them in real time as you adjust their parameters.

Any or all of the Bias tools can be applied in the Preview mode. This allows you to hear the combined or individual effect of all of the tools.

Bias has also innovated a new design for their broadband noise reduction tool. The graphical user interface has twelve sets of sliders for adjusting the threshold and the degree of noise reduction.

As with other noise reduction software, the user first takes a sample of noise from the sound file. When this is done, the software sets the threshold and degree of noise reduction automatically. The software also divides the noise into 12 frequency bands based on the unique characteristics of the noise sample. The attack and release times can be adjusted and two “tilt” knobs provide further adjustment of the ratio of the attack and release times between the low and high frequency bands.

Because each sample noise is unique, the 12 bands into which the noise is divided are unique for every individual noise sample. Each of the twelve sliders controls the threshold and the amount of reduction for a particular band.

The user can tweak the settings while previewing the results in real time. The twelve sets of sliders can be locked so that all threshold and all reduction sliders move in unison, or they can be unlocked allowing the user to adjust each slider individually.

At first this approach felt awkward. After working with it for a while, I found adjusting the individual sliders to remove remaining noise as intuitive as it was effective.

The advantage of 12 individual sliders for adjusting both the threshold and the reduction is that you can pinpoint the offending noise spectrum without affecting other areas of the frequency spectrum.

The Bias approach is clever in that it provides an advanced means of removing specific areas of noise while keeping the overall operation simple. This is in keeping with Bias set goal: “. . . to provide professional-quality audio restoration but also to be very simple to use. . .”

I found that it was relatively easy to remove both impulsive and broadband noise using SOUNDSOAP PRO. The results were very good -- essentially comparable to results I achieve with other noise reduction software, and in some cases -- better.

Noise Gate

Bias has incorporated a Noise Gate into SOUNDSOAP PRO. Frankly, I have been waiting for someone to do this as experiments that I have done in chaining a noise gate to other existing broadband noise reduction software have been promising.

Now that someone has actually done it, does it prove helpful? The answer is “Yes!” I found that it took some time to learn how to set the parameters of the Noise Gate, but once I did, it was helpful in eliminating remaining noise that occurred at low levels.

Bias has created a helpful visual indicator that allows you to see in a graphic format exactly where the noise gate takes effect in relation to the sound level. By watching the visual display and listening to the sound while adjusting the threshold knob, it is possible to tweak the sound to eliminate low level noise without adversely affecting the sound itself.

The only remaining question is, why haven’t the makers of other noise reduction software done this before? I will be surprised if others don’t soon follow Bias’lead.

The Click and Crackle module is probably the easiest to use. It has two controls: a Click Threshold slider and a Crackle Threshold slider. Adjusting the sliders increases or decreases the aggressiveness of the respective controls. I found that together the two controls are able to remove most impulsive noise found in long play records and electrical transcriptions. A click meter flashes in red to give a visual indication that the software is removing pops and clicks.

Removing Hum And Rumble

The Hum and Rumble module is the first of the four modules in SOUNDSOAP PRO. The hum portion functions essentially as a notch filter and contains three controls. The Frequency slider determines the fundamental frequency at which the filter is applied and can be adjusted over a range of 20 to 196 Hz. The Q Slider determines the bandwidth that will be affected by the filter and the Depth Slider determines how deeply the filter will be applied.

Bias has added a Hum Meter that works in conjunction with the Frequency slider. As the Frequency slider is adjusted, the Hum Meter’s red line will increase or decrease in proportion to the amount of hum at a given frequency. This helps the user to set the Frequency slider to the exact frequency at which the hum is greatest.

The hum portion of this module also contains a Harmonics slider that enables the user to apply the notch filter to as many as nine harmonics of the fundamental frequency. In addition, a Tilt knob allows adjustment of how deep the subsequent harmonic frequencies are cut.

The Rumble filter is a single slider calibrated in Hz that enables the user to remove rumble and related low frequencies over a spectrum of 20 to 500 Hz. It has a fixed slope and Q value.

The Hum and Rumble module proved effective in removing both hum and other low frequency noise. At 96 Khz/24 bit sampling rate, the Hum module did not work properly, but Bias has promised to fix this problem in a free update that may be available by the time you read this.

I would have liked at least some of the SOUNDSOAP PRO’s parameters to be automatable. I’m told that in some versions of the plug-in, they are. Currently they were not automatable in Sound Forge 7.0 that I used as the host application.
Overall I rate SOUNDSOAP PRO as a high quality noise reduction plug-in that is very user friendly and capable of producing good quality audio restoration. The low learning curve, ease of use and the high quality of the restoration should make this a welcome product for many kinds of radio production.

Whether you are looking at your first noise reduction software, or want to add another tool to your arsenal of noise reduction tools, SOUNDSOAP PRO represents a “sound” investment at price of $599.

-- The End --

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

BIAS, Inc., 1370 Industrial Avenue, Suite A Petaluma, CA, 94952, USA Voice: 1 707 782 1866 Fax: 1 707 782 1874 E-mail: sales@bias-inc.com

Product Capsule:
Digital Audio Restoration Plug-In
Thumbs Up:
Easy user interface
High Quality Sound
Logical arrangement of tools
Broadband Noise Reduction provides ability to target specific areas of noise
Includes noise gate for added noise reduction
Hum module targets both hum and other low frequency noise

Thumbs Down:
Parameters not automatable in some versions
Bug in Hum module at 96 Khz/24 bit sampling rate