Xref: utzoo comp.misc:5133 rec.music.synth:6132
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!apple!amdahl!drivax!macleod
From: macleod@drivax.DRI (MacLeod)
Newsgroups: comp.misc,rec.music.synth
Subject: Re: Computer Restoration of Older Recordings
Message-ID: <4284@drivax.DRI>
Date: 15 Feb 89 00:46:04 GMT
References: <1912@helios.ee.lbl.gov>
Reply-To: macleod@drivax.UUCP (MacLeod)
Organization: Digital Research, Monterey, CA
Lines: 7

Phase Linear had (has?) a technique where the system looks for energy above
some figure - say 14 kHz - and assumes that it is a second harmonic of 
something.  If it doesn't find energy at 7 kHz, it flushes the 14 kHz signal.
You could work this in reverse to add harmonics to heavily-filtered input.

Phase Linear was doing all this, as far as I know, with analog circuits.  It
should be a lot easier to do digitally, and a lot cleaner as well.