Pump Up the Volume, Not the Noise
Sometimes noises are good, for example if you are trying to isolate a component which is intermittently failing. Each crackle and hum gets you closer to your goal. But usually noises are bad, such as those on your old tapes that almost drown out the program material.
Audio can be infected with all manner of colorful background hums, crackles, pops, and that all-time analog favorite, hiss. Some audio which you hear every day even on national newscasts is marred by fluorescent light hum, air conditioner drone or even crowd hubbub.
There have been a number of software and hardware products designed to deal with these irritants, but my friends, say hallelujah, now there is renewed hope of ridding your audio of these unwanted guests forever.
Fingerprinting solves crimes
A British company called CEDAR Audio makes a variety of sound restoration tools which are pricey but extremely effective. This article will deal primarily with Cedar De-Noise, which is available only through SADiE, another British company whose U.S. headquarters is in Nashville. This product is very helpful in eliminating or at least greatly reducing any constant background noise. Other more esoteric flaws in sound such as drop-out, tape squeal, phase shift and azimuth problems will have to wait for a separate article.
Unlike hardware products such as those made by dbx and others which allow the user to simply set a threshold and then gradually or suddenly gate all audio below that level, CEDAR works on a different principle.
The user samples the noise source prior to or in-between the desired audio segments by holding down the mouse clicker for about a second, and CEDAR makes a digital fingerprint of the background noise. Then itís a very easy matter to manually slide down the "attenuate" fader onscreen until you achieve the result you are looking for.
Music minus hiss
My typical application is removing hiss and occasionally hum from audio tapes recorded in the sixties and seventies. Sometimes the hiss is barely noticeable, but sometimes it makes a second or third generation dub almost unlistenable.
Our digital workstation is made by the afore-mentioned SADiE and I start the process by loading our program material through the analog ports. SADiE lets you look at the audio onscreen in colorful solid blocks, or with the click of a mouse, as waveforms which clearly show the main audio and the spaces between. This will come in handy in a moment.
In our case, we are restoring PAMS ID jingles recorded in the halcyon days of Top 40 for AM stations such as WLS, WABC, WFIL and others. When viewed onscreen as wave forms, a jingle package of twenty cuts is seen as red squiggles representing the music with :04-second gaps between them, representing the alleged silence between the cuts. For purposes of this article weíre using jingles from Radio Luxembourg with a moderate level of hiss and hum, which is mostly apparent between the jingles, but is clearly present through soft passages in the music itself.
Once the jingles are recorded onto SADiE, I access the CEDAR module by clicking on the processing icon, selecting CEDAR De-Noise and bringing it into the path of the virtual mixer. Now the fun begins.
As I listen with CEDAR bypassed to the first several seconds of the package prior to the actual first jingle, I can hear the noise I want to get rid of. As I play through that section onscreen, I briefly hold down the "sample noise" icon between cuts. A small box immediately pops up with a digital picture of the offending hiss and hum, featuring dB as the vertical aspect of the scale and frequency in Hz as the horizontal. This particular noise has a hum component centered around 60 cycles. It also has a hiss component centered around 3200 kHz. But no matter, CEDAR is about to greatly improve both in one pass.
Again playing through the audio, this time manually lowering the attenuation fader as I go, I hear the junk disappear as if by magic. Let me pause here to say that Pro Tools offers a module which is designed to work in a similar manner, but in my experience it twists and muffles the desired audio with as little as a few dB of noise reduction. The Pro Tools software causes strange, echoed and distorted artifacts and a tremendous loss of high end content. It also eats reverb trails, twisting them into something very unpleasant. Not so with CEDAR.
Like a laser which kills cancer cells but leaves healthy cells, CEDAR De-Noise zeros in on and gets rid of at least 10 dB of noise, and in some cases as much as 20 dB without affecting the jingles in the slightest. This is enough to save all but the most hopeless audio. From this point it is a simple matter to "bounce" the entire audio chunk through CEDAR with the level of noise reduction I want, replacing the original flawed version of the jingles in the edit decision list onscreen.
I own one tape of some people horsing around in the PAMS studios, and everyone is at least ten feet from the microphone. Itís a second generation dub made on ľ-track machines in 1972, but it is historically interesting and I wanted to see if I could salvage it by removing the almost unbearable hiss.
After sampling a portion of the noise alone, I began attenuating. At about 10 dB a great deal of the noise went away and the voices still sounded very natural. At about 18 dB down, most of the noise was gone, but the voices took on a rather Martian distortion. It was much easier to hear every word clearly, but it was like looking at an image in a fun house mirror. Following a suggestion by a SADiE tech, I bounced the audio with about 10 dB of attenuation, then resampled a slightly different section of noise and did a second pass with CEDAR taking out about another 5 dB of noise with very good results.
Several years ago I did some consulting work for the Toledo police, filtering out noise from audio surveillance tapes. I didnít have CEDAR then, but I did the best I could using parametric EQ with moderate results. The key there was just to be able to understand what was being said. The De-Noise module is much more accurate and would be perfect for that sort of use, even if it distorted things a bit. A jury only needs to hear the words and a little "over the top" attenuation wouldnít hurt anything.
From the source
I was so amazed with the product that I contacted Gordon Reid, managing director of CEDAR Audio who explained that its success comes down to the quality of the signal processing algorithms.
"Itís relatively easy to remove unwanted sounds from a signal. Whatís much more difficult is to detect these in the presence of a desired signal, isolate them and remove or reduce them without introducing unwanted artifacts," said Reid. "You can remove all of the unwanted noise by just turning down the amplifier to zero, but that also removes the signal. So itís not how much noise you remove that matters; itís the compromise between noise reduction and the unwanted side effects."
Other features are helpful
The CEDAR software lets you improve on nature by manually redrawing the noise fingerprint if you so desire. It also lets you store and recall settings you come up with which might be reused. Within the SADiE system, you can zoom in and out on the fingerprint onscreen to see more detail. CEDAR De-Noise works in real time because the company believes it is vital for the engineer to hear the processing as it is performed.
In additional tests on different types of constant noise sources, CEDAR did very well. I found that sometimes, only 5 to 10 dB of noise reduction is sufficient to clean up a voice tape and make it easier to understand. Hiss and hum were very successfully reduced in all cases with littler or no effect on the underlying audio.
The biggest advantage to CEDAR is that it is very gentle to music, leaving the highs alone and not twisting up the percussion. In fact, it is almost impossible to notice any effect on music in most cases.
CEDAR recently introduced the DNS 1000, a new tool for dialogue clean up which is used at Skywalker Ranch, Fox, Universal Studios and Disney. Other CEDAR audio restoration modules include De-Click, De-Thump and De-Crackle. In addition to software solutions, the company also makes its products available as rack-mount modules.
While it may be difficult to tell the music from the noise in many contemporary rock songs (please excuse the nasty personal opinion), undesired noise can certainly be greatly reduced with CEDAR products.
De-Noise module thumbs up:
Tremendous surgical ability to remove constant noise sources from recordings
Little or no damage done to underlying audio
Flexible; can remove hum, hiss or even high frequency whine with ease
Can process mono or stereo source material
Operation is so simple that even I can figure it out
De-Noise module thumbs down
Darned expensive for software (about $2500)
Can produce odd artifacts if used to extreme
Only useful for constant noise sources; will not remove background TV audio from a
voice tape, for example which might also be considered an advantage
The process is not entirely automatic, a certain degree of skill and taste are needed.
Now you can have Ken clean up any noisy or damaged audio of your own! whether it's on reel, cassette, even vinyl
Ken R. is a former broadcaster and jingle studio operator who can be reached at firstname.lastname@example.org