Xref: utzoo rec.audio:7395 sci.electronics:3395
Path: utzoo!attcan!uunet!husc6!uwvax!oddjob!ncar!noao!tody
From: tody@noao.arizona.edu (Doug Tody X217)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Restoration
Summary: restoring old recordings
Keywords: loudspeaker, speaker, bibliography
Message-ID: <812@noao.UUCP>
Date: 21 Jul 88 08:09:05 GMT
References: <1309@kodak.UUCP> <6198@aw.sei.cmu.edu> <2585@obiwan.mips.COM> <4867@vdsvax.steinmetz.ge.com>
Organization: National Optical Astronomy Observatories, Tucson, AZ
Lines: 57

> >In article (Paul Gallagher) writes:
> >Here's a question maybe someone out there can answer:
> >Why isn't it possible to completely restore a recording: for example, 
> >to removeall extraneous noise (hiss, clicks, coughs)

It isn't possible to completely restore old recordings given current signal
processing technology and algorithms, but the following is a recent
development I found interesting.  This is a new line of CD's by Phillips
called "Legendary Classics".  Here is a quote from the liner notes in one
of my disks:

	Historical recordings by such legendary musicians as Ravel, Casals,
	Prokofiev, Van Beinum, Souzay, Oistrakh, and Richter, now lovingly
	restored to their original majesty thanks to Sonic Solutions' NoNoise
	micro-technology and Philips remastering and digital expertise.

		    The Artistry of the Past Now Made Perfect
	For Philips exclusive Compact Disk Collection of Legendary Classics

Well, of course it isn't perfect, but it is the most interesting commercially
available development I have seen in this area.  The difference in the sound
is very noticeable - doesn't mean you will like it though, many people won't.
There was a review of the technology in a recent Grammophone...  

Here is a brief description of the process from the liner notes before me:

	...Developed ... at Sonic Solutions, in San Francisco, Calif...
	NoNOISE can remove surface noise, tape hiss, clicks, and pops and
	other unwanted noise without affecting the original.

	...The digital data is then transferred to large computer disks and
	engineers at Sonic Solutions assess the problems, using special
	analytical programmes...

	If the recording contains clicks and pops, they employ a programme
	which incorporates techniques developed in artificial intelligence
	research [I'm just quoting this, don't blame me...].  This identifies
	the clicks or pops and recreates sound to replace the area they
	occupied.  Since the area is reconstructed rather than removed, the
	precise duration of the original performance is preserved.

	To reduce surface noise or tape hiss, ... analyze the spectral
	composition of the underlying noise floor.  Over 2000 points in the
	audible spectrum are measured to yield an accurate estimate of
	the unwanted noise.   This is then used by a special computer
	programme to perform "micro surgery" on the sound to reduce the
	noise without affecting any subtlety of the original.  Over 53
	million separate computations...  [etc.]

This is rather overstated, but an interesting experiment nonetheless.
I have only one such disk thus far - it is very good sound for such an
ancient recording - 1928, 1932, 1938, all mono (the Ravel and Prokofiev disk).
Unless you are interested in these ancient performances, however, any well
recorded modern performance is going to provide much better sound.

	Doug Tody
	NOAO, Tucson