CEDAR Single-Ended Noise Reduction System (part 1)
How fortunate we are to have audio recording media such as quarter or half inch analogue tape with Dolby SR noise reduction, DAT, 1630 and the various other digital formats that are currently available. We can capture sound with an almost incredible accuracy and, with due care and attention, be sure that no intrusive background noises, other than an almost non-existent hiss, will mar our listening pleasure. And with Compact Disc, this degree of perfection extends right down the audio chain all the way to the domestic and even to in-car and personal stereo users.
Things havent always been so good. Remember the days when your record collection was your most prized possession? And remember how it felt when you lent a disc to a friend and it came back with an ugly scratch all the way across your favourite track? And do you remember how an old fashioned black disc could be perfect one day, and the next time you played it the music could be almost obliterated by a swarm of tiny but irritating clicks? I could go on to remember the times I have spent in record shops complaining that the disc they sold me wasnt perfect, and received the answer, which could be phrased in one of a thousand ways but always meant, Well thats just the way things are and youll damn well have to learn to live with it. These are not happy memories.
The Holy Grail of the record collector, then and now, has always been a device which could somehow magic away all the unwanted crackle and let you listen to just the music. There have been plenty of attempts over the years to invent such a device, but until very recently none has been successful enough to convince critical listeners. Manual methods, such as copying onto tape and cutting out the scratches, have had some success, but it is inevitably a very labour intensive process and it can only deal with very major blemishes on records.
Over the last couple of years we have been hearing quite a lot about a process known as CEDAR which claims to remove clicks an d other non-musical events from old recordings, and there has been some interesting discussion in Studio Sound recently (May and July 1990) which I do not propose to elaborate on. I hope in this article to describe what CEDAR is and what it does, and give a personal impression on how well it performs. The precise details of how the process works involve high flying mathematics which must wait for another day.