You may be referring to the Phase Linear "Autocorrelator 1000"
These were mfgered in the late 70's, and early 80's. They had an open ended noise reduction circut to reduce surface noise (clicks and pops) on records, and also helped reduced tape hiss, and a dynamic range expanding circuit.
They worked fairly well, I still have one that dosen't function any longer.
There is usually 2 or 3 available on EBAY most of the time ... can be had for under $100 most of the time. Make sure you get the manual with it.
From the Phase Linear site ... please view link for picture. PHASE LINEAR SITE
Phase Linear offered a number of other components other than amplifiers, pre-amplifiers and speakers. (When speaker information and photos are available, I will add them to the website). The line expanded considerably after Pioneer purchased Phase Linear. Here are a few of the lesser known Phase Linear components.
Model 1000 Autocorrelator Noise Reduction System
The Phase Linear 1000 Autocorrelator Noise Reduction & Dynamic Range Recovery System was a stand-alone component. It was introduced in the mid-1970s to complement pre-amplifiers that did not have this circuitry.
Model 1000 Series Two Noise Reduction System
The model 1000 Series Two was introduced in 1978, replacing the original 1000.
The best of the bunch was the Burwen Research TNE 7000A Transient Noise Eliminator, also marketed under the KLH name. This is the unit that most recording studios had in their racks. They're available on Ebay for around $120 usually. I have one, but have never tried it out, so I can't give any firsthand feedback.
My plan was not to use it for listening, but to use it while burning any noisier lp's to CD, to cut down on the amount of manual declicking necessary in the computer. (The noise detection/elimination software is far from perfect, so there can be substantial work in finding and fixing clicks in the PC.)
p.s. If you don't mind the use of "black boxes" (unlike many diehard audiogoners) and you want to improve the sound of your vinyl, the unit to have is the DBX 3BX-DS (or the 4BX or 5BX). Properly used, it will WOW you!
Yes such devices have been manufactured. Back in the 1970s a company named Burwen put out two units, one for tape hiss, and one for clicks and pops. In the 1980s and 1990s a company named Packburn in Dewitt, NY (near Syracuse) put out the Packburn Audio Noise Suppressor Model 323A, which had a stage for diminishing hiss as well as a stage for diminishing clicks and pops. For a while it was listed in Stereophile's "Recommended Components." Stereophile called the Packburn "the Cadillac of nose suppression units." I ended up getting one directly from the company for $2,400. As the years have passed, it has developed a hum. Whether the hum is an internal issues, or whether there is an externl factor, I don't know. I haven't try to deal with it seriously because I now transfer my LPs to CDs using Sony's Sonic Forge software.
Burwin noise reduction used during the 1970's. Dan at Arizona Hi-fi [in Mesa, a suburb of Phoenix] used to refurbish these units, but that was a few years ago. If you're interested, you can contact him at 480-921-9957
SAE offered the Impulse Noise Reduction System. There are two currently ending soon on EBay, one model 5000 and a 5000A.
I went to Google and typed "Packburn." There are quite a few sites dealing with noise reduction devices. Might be worth some of your time.
Thanks to all of you for your help. I will follow up on all your suggestions.
At one point or other I tried all of the above with the exception of the Packburn, and found they all simply did more harm than good. I would think that now something much better would be possible in purely digital foremat, but have no idea if anything is.
There were many noise reduction units marketed several decades ago, aimed at rumble, surface noise, pops, clicks, and dynamic range expansion and peak unlimiting. Some, like Bob Carver's Autocorrelator, were very "clever". All worked reasonably well, but none were perfect. Today's vinyl fans prefer to say that all these LP problems either don't exist or can be eliminated by some rather exotic and expensive turntables, pickups, and arms. Whatever...
The only really good way to restore old LPs is to play them back as well as you can, and digitize the signal. Once that is done many techniques can be used that are quite impossible if you try to do the cleanup in real time (while the LP is playing). An example is playing the music backwards. Music has leading edge transients that are similar to clicks and pops, but music has no trailing edge transient...the sound dies away over some time. If you analyse the digital signal forwards and backwards, the clicks and pops, which are transients both ways, can be distinguished from musical transients which only occur with forward playback. I have not actually used this type of LP cleanup software, but the results I have heard far exceed those of the old boxes of electronics.
Eld, music is filled with trailing AND leading edge transients. For example, an acoustic piano has not only a sustain pedal but a mute one too. Likewise, string players use their palms to mute vibrating strings and resonating wood. These mutes create trailing edge transients, a necessary ingredient in the production and reproduction of music.
Rockvirgo...The Mute function performed by a musician, although it may sound abrupt, is too slow to be called a "transient". The fact is that the "play it backwards" approach to click elimination does work.
I suppose that some sort of electronic mute could be used that would chop the waveform off as sharply as a scratch in the LP.
And...the electronic mute would have to be something done by the recording engineer, at his console, not by the musician. Even if an electronic instrument's output were chopped off, the sound would linger on in the hall.
Eld, good observation. Like the response to impulse tones some testers seem fond of, I suppose music or any sound created in air necessarily has certain reverb and decay components. Whether recording and playback captures, lessens or enhances those qualities for us back at the ranch makes interesting food for thought.
Your further responses are intriguing to say the least. I have also been told that scratches may have a certain regularity, i.e. every revolution for the duration of the scratch if perpendicular to the edge which also opens a possible avenue for a sophisticated software program to recognize and minimize. I am writing again here primarily to ask if any of you who wrote above or anyone who hasn't written yet knows of any "backwards and forwards" noise minimizing software and/or any other equally sophisticated software actually on the market or under development and where I might locate or at least who to contact. Thank you.
email@example.com...I don't consider myself a "hands-on" expert on this subject. I have heard lectures on how digital restoration of LPs works, and have heard some "before/after" playback that was astonishing. There are many techniques other than the "forwards/backwards" one...I picked that one as a good example of something that obviously cannot be done while the LP is playing.
Regarding software for your PC, when I looked into this I found a range of price from about $39.95 to $400. You probably get what you pay for. I don't know if the "forward/backwards" technique is included in any of the consumer software.
I've done a fair bit of "restoration" on some rarer lp's that are not easily replaceable. The software packages are a good start, but if you want perfection, you have to go in and redraw the waveforms manually. So I can tell you one thing - if the lp is replaceable at reasonable cost with a mint copy, that's the way to go if you value your time.
Eliminating virtually all noise on a VG- lp can take me about 16 hours of work.
The software has basically two functions: 1. find the click and 2. repair the click
The reading backwards approach will help in automatically finding clicks with less false positives. But no software is foolproof in that regard, and in addition, they all miss a lot of smaller clicks. Many clicks are not as sudden a transient as you might think, because they are compound problems - not just one isolated spike. Also, as the source music frequency rises, and the click magnitude and duration decrease (like "surface noise") noise becomes much more difficult for software to differentiate from the music. So to really clean up a moderately noisy lp you have to sit there with headphones, listening, looking at the wave trying to find the clicks which your software misses - and this can be very time consuming. Many small clicks are maybe 1/8000th's of a second in duration. Finding those in a five second snippet of music is not as easy as one might assume.
As to the repair function - software has maybe 30% of a human's intelligence when it comes to figuring out what SHOULD be where the click was. To fix a noisy section, it has to either apply some form of smoothing to the click based on a user definable algorithm, or interpolate what exists on either side of the damaged area, or outright copy and paste in a different area of the waveform. A human can just draw in what looks and sounds right with a much better reult. But this is very time consuming. Another problem with automation is the "repair" of false positives (especially as Eldartford correctly surmised, with electronic effects), which can really detract from what you're trying to do.
So the bottom line is - if you want an "acceptable" MP3 quality result for convenience, than probably any of the popular programs you find on Google will be fine. But if you want it really, really right, the software is just the jumping off point. (And you're wife probably won't be jumping with you :)
If you want to try one for free to get your feet wet, a good start is WaveRepair, which was written specifically for vinyl lp repair, and is excellent for manually redrawing waves. It's not so great at detection unfortunately so it's a mixed bag. It has a 30-day free trial that you can download and be playing with in 10 minutes:
It's not a full function, consumer-level, sound editor though and isn't great for quick, automatic fixing. I've become attached to it though.
I've also been meaning to try out Audacity which is totally free shareware, but haven't yet:
Hope this helps, Chip