Restoration (a/k/a Re-mastering)
Fabric reweaving. Scratch removal. Brick repointing. Reframing. Furniture regluing. Organ transplant. From the sublime to the ridiculous, people fix, reclaim and restore broken stuff all the time. So when the enjoyment of a recording, old or new, is impaired or impossible due to physical defects or old age, you should consider a restoration of the ailing audio.
It is not the sound per se but the storage medium that is falling apart. Most important, therefore, is to arrest the decline of the medium at once, so as to buy time to plan the best course of action leading to the recovery and/or reconstruction of the deteriorating audio.
Tapes and disks develop problems for all kinds of reasons. Some problems are related to the natural decaying of a storage device (tape; disk). Some are caused or exacerbated by the wear and tear of playback mechanisms (tape player; turntable) on those storage devices. And some are atmospheric.
A client recently brought in a beautiful five-minute recording of a very exciting vocal performance. Recorded live. In a thunderstorm. In a thunderstorm with lightning.
Lightning. As in 'electrical disturbance.' Our mission was to remove 'a few tiny clicks' which occurred as lightning struck nearby throughout the recording. Client brought in a list of timings to point us to the 'seven or eight' spots where the ticks were apparent to them. Analyzing the tape using one of our Sonic systems, we soon made two important discoveries:
- That each of the noted spots contained not one, but between 5 and 10 ticks, strewn about the stereo image; and
- That the performance was completely _riddled_ with ticks. Zillions of them. And the more single ones we removed, the more new ones the client heard! This was yet another confirmation of what we affectionately call "Tucker's Lint Theory".
A furious declick and decrackle session ensued, and the patient was cured. Not a razor blade in sight. And no blood was shed.
Tucker's Lint Theory
"Tucker's Lint Theory" holds that if you observe someone wearing a black jacket which has a piece of lint on it, and you step forward to remove the lint, the act of stepping closer to the jacket causes you to see other, smaller particles of lint, which, of course, you wish to remove. So you step closer to do this, whereupon you see even smaller particles of lint,....... You must stop this foolishness at some point and step back or the jacket will be destroyed.
Click removal is accomplished via a technique called 'interpolation' in which we identify a problem area in the music, and direct the system to compare what it finds there with the music immediately before or after the problem. Following a set of rules (an algorithm) indicated by our engineer, the system redraws the problem zone to eliminate the distinguishing characteristics that differentiated it in the first place from the surrounding music. The non-musical event (click) is now removed. Clear as mud? But it works. And no audio is lost or changed. Works as well on 78rpm transfers as it does on lightning.
Broadband hiss is another major problem we are often asked to fix. Sources of hiss include:
- analogue tapes made without noise reduction
- low level recordings
- pre-amps and outboard gear in record/mix loop
- transfers from disk (Vinyl LP, 45rpm, 78rpm, et. al.).
In the Dark Ages (pre-1980's) hiss was reduced either with equalization (eq), which took out much meaningful musical tone along with the hiss, or processes like the infamous Burwen, which was essentially a variable noise gate, and took out much meaningful musical tone along with the hiss. The Burwen let signal go through when signal was loud (and noise was somewhat masked) and shut down gradually as signal strength weakened. We weren't supposed to notice that quieter musical passages grew very dark without their upper octaves! But, hey! It's what we had. (In fact we still have one.)
Nowadays, broadband hiss is dealt with by taking 'fingerprints' of the noise, thereby identifying the components of the hiss, and attenuating (reducing) only the noise components while leaving the musical content untouched. Pretty cool.
It ain't automatic. But in the right hands (guess whose?), it works.