Quote:
Originally Posted by TIMTAPE
The old analog NR systems like Dolby, DBX, ADRES, ANRS, HiCom, Burwen could work well not because they were analog, or because they were old, but because they were double system, or companders. They pushed the programme above the system noise at the record end, the only place to do it. Then the playback decoding merely undid the compression.
Trying to expand down unwanted noise at the playback end is doomed to failure if unlike double system NR the recording was never intended to be expanded on playback. The result will never be transparent. All we can do is use it very sparingly and hope that not too many people notice the artifacts. It's not the fault of the tool. It just has an impossible task.
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Whoa! Concealed assumption alert.
Mere complementarity does not an inaudible noise reduction system make.
Simple compansion around a noisy channel, be it analogue, digital or pink with purple spots, isn't a particularly good idea. Every analogue noise reduction system apart from Dolby has audible artifacts under some real-world conditions, usually on piano or bass guitar. If Dolby isn't lined up properly, you can hear that working, too. The art of it is to use the characteristics of human hearing to mask the noise modulation effects - Dolby A and SR use multiple bands, Dolby uses a sliding turnover.
The point of such as CEDAR NR-5 is to get the maximum subjective effect for the minimum actual interference with the signal. Thus, on a shellac 78, I can apply a gentle dip in the noise in the low kHz, where it is most troublesome, whilst leaving lower frequencies, with their ambience and reverberation elements, severely alone. The effect of this is not to reduce the noise to nothing, but to render its spectrum white or pink, something the ear recognises from nature and therefore discounts to a greater degree. Subjectively, the noise retreats behind the music and ceases to be annoying, without that ghastly processed sort of sound so beloved of some in the field. The trick here is to have enough frequency bands and to tailor the dynamics of the reduction process so that the ear masks the mechanics of the process - as Ray Dolby did, fifty years ago.
To my mind, if you can hear the processing in sound restoration, you have done a bad job. Excellence in this field consists of using the best tools with the lightest touch consistent with a natural-sounding result. In the nature of the beast, this results in noise amelioration rather then elimination, certainly as far as steady-state noise is concerned. However, nearly every transient disturbance can now be removed without audible damage to the wanted sound, given sufficent patience.