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  • Tape Restoration Bliss!

    Hey all!
    Have not been to the site since last winter (I was in a treasure hunting mode through the summer...) so I have a lot of posts to catch up on. (Hope I'm not rehashing old subjects...)

    I've been restoring some of my old reel-to-reel collection lately. DC6 is absolutely wonderful for my needs, but I've had a few quirks. I have been using a Pioneer RT-707 for playback of these tapes, which was the same brand/model I used to record them back in the early 80's. (found it on eBay in nearly unused condition - heads don't even have the beginning of a cut in them!)

    I used the suggested procedure for recording a White Noise signal on one of the tapes to play back and obtain the response curve of the deck/tape using the DC6 Spectrum Analyzer. The only thing I did different was I set the Spectrum Analyzer to 20db scale (not the suggested 100db), and I streched out the Analyzer view to fill the entire screen. I didn't have a new tape to work with, so I recorded it on an unused portion of a tape not played often. The Spectrum Analyzer is extremely slow with my old PIII-500, but otherwise it still seems to work fine. (It takes it 2 hours to test a 10 minute signal!)

    Using the Multi-Filter consisting of 4 seperate Paragraphic EQ's and a Low Pass Filter (yes - a low pass filter!), I was able to come up with a curve for each channel that was nearly 20 to 20,000Hz +/- 0.5db! (Not too shabby for 3.75 IPS!) If not for the slight rise at about 19,000Hz, the response would have been better than +/- 0.3db! Please note that most tape deck manufacturers (including this one) only claim response specs at +/- 3db - The end result exceeded the performance of the deck itself!

    The reason for my using a low pass filter (19,999Hz @ 12db/octave) was because when I tried to counter the playback EQ, I ended up with a sharp rise in the response starting at about 17,500Hz that peaked to about +6db at 20 to 22kHz. I am not sure if it was the limitations of DC6 (or my "antique" computer), but I had trouble setting up the Paragraphic EQ above about 12,000Hz. The "view line" on the EQ would pop away if I tried to narrow the bandwidth or increase the frequency. Correction or improvment of this in DC7 would be a greatly appreciated. It would also be nice if the Spectrum Analyzer would go beyond it's 20kHz (21, 22k?) limit for people restoring CD-4 LP's.

    After finally comming up with the response curves, I put on a dbx encoded tape on the deck and fed it into the computer. I applied the Multi Filter frequency response corrections to the seperate channels, & then used DC6 to playback the processed signal out of the sound card into my outboard dbx decoder. At the same time, the decoded signal was fed back into the sound card input, where I used a second instance of DC6 to re-record it. After reviewing the fully processed recording, I nearly forgot I was listening to a recording from a tape as it sounded more like the original LP! I was even able to remove most of the clicks & pops from that 27 year old LP tape copy! Wonderful!!!
    The dbx decoder tracked quite well with the EQ processed signal, but was a bit excessive and crisp in the treble end. I believe this was because the tape that I used for the test signal was in fact old & used, which may have reduced the treble response of the test. I have found a factory sealed NOS (new old stock) Maxell UD 35-90 on eBay which I will be receiving in a few days, so I will re-do the test and offer the presets in the near future at the forum for anyone with one of these old decks using this tape. Other than the few quirks I encountered, I was impressed with the results.

  • #2
    Hi DJ!

    Great to see you back here. I was wondering where you were.

    Anyway, the paragraphic EQ top band is a shelving filter, unlike the others. As a result of that fact and the math and sampling theorem, I believe the the highest that you can put the shelf is around 11 KHz. It is just the math.

    As for calibrating your tape deck, it has been my experience that each different brand and type of tape yields slightly different frequency response characteristics. So, if you calibrate, say with an Ampex tape, and then play a TDK or Maxell with the Ampex EQ, the results will not be exactly flat - - - but close.

    As for that bump at the top end, that is not uncommon. It involves the wavelength of the signal coupled with the coloidal partical size used in the tape emulsion. But, it sounds like you compensated for it reasonably well.

    ps - I think that your presets for different speeds is still number one on the hit parade on the presets sharing portion of the forum. Go check it out. I have not looked carefully in a few months, but this past summer, that was the case.
    "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

    Comment


    • #3
      Originally posted by Craig Maier
      Hi DJ!

      ps - I think that your presets for different speeds is still number one on the hit parade on the presets sharing portion of the forum. Go check it out. I have not looked carefully in a few months, but this past summer, that was the case.

      Yes, welcome back, DJ.

      I hadn't paid attention to the preset downloads before, but now that I see Craig is, I'm going to have to come up with some that will beat your record! I think a catchy title would be good. Maybe something like 'general audio restoration preset' would do it!

      Dan
      Dan McDonald

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      • #4
        Thanks for the quick response Craig - it's nice to be back at the forum!
        Back 20+ years ago, I pretty much stuck with the Maxell UD 35-90 tape - nearly 20 in all. I have only 3 Maxell LN 35-90's, 1 UDXL 35-90B, a couple of Memorex, 1 Ampex Grand Master & a handfull of Radio Shack tapes. I felt at the time the Maxell UD was the best choice for overall quality. But if it hadn't been for occasional dropouts & poor quality control, the best sounding tape I had ever used with the Pioneer was the (heaven forbid!) Radio Shack Supertape! I believe this is because Radio Shack paterned their tape after the Scotch (301 or 311?). The Pioneer deck was also designed around and calibrated to that same Scotch tape. Oh well! I will just be glad when everything is transfered over to CD so I can be done with all these old tapes all together. But then I will have my Cassette collection to go through...

        Comment


        • #5
          My favorite was the UDXL also, but I did have some radio shack supertape. I always thought it felt like it wouldn't last very long, but so far every one I've transferred (no matter what brand) has been fine, and they were all recorded between 1971 and 1976.

          Dan
          Dan McDonald

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          • #6
            Hi Dan! I could only wish I had a R2R back then. I purchased my original Pioneer in 1979. I would love to have had some good recorded radio broadcasts of "Beaker Street" & "Beaker Theater" from KAAY-Little Rock, Ark. or WLS-Chicago, especially when they did the "Top89" hits of the year every new years eve. (You don't have any of these do you? Would love some copies.) I found someone who had the "Top89 of 1969", but he sent me cassettes that were copies of copies of copies etc., which I have found the sound so degraded they were nearly impossible to restore. Anyway, it's nice to be back and to hear from you guys again!

            P.S. Dan - Good luck on your preset "Holy Grail" (Yuck yuck!)

            Comment


            • #7
              Originally posted by Dan McDonald
              My favorite was the UDXL also, but I did have some radio shack supertape. I always thought it felt like it wouldn't last very long, but so far every one I've transferred (no matter what brand) has been fine, and they were all recorded between 1971 and 1976.

              Dan
              Having run a Radio Shack back in the day, I can speak on the issue of any "Radio Shack" branded merchandise. It was (tape, audio gear etc) Radio Shack in name only. They just "private labeled" merchadise like Wal-Mart, Target and all the other chains do as a norm now a days.

              And Yeah, I liked the RS Supertape pretty well too, but the UD's were the best in my book at the time.

              GB

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              • #8
                I pulled out one UDXL today and it's still like it's brand new - I always kept the plastic bag around it, and its still there - maybe 30 years old? The other day I pulled out a record album and a decal dropped out of it - from 1972. I always tried to keep everything together. Anyway, the supertape looks a little fringey at the beginning, but still looks good. I've also got some Shamrock tapes, Memorex, etc. But Maxell was always the best.

                Dan
                Dan McDonald

                Comment


                • #9
                  I remember, when I was a kid of 14 working as a technician at the local high - end "Hi - Fi" shop*. I worked on a lot of high - end audio equipment including tape decks like:

                  1. Ampex
                  2. Magnecords
                  3. Crowns

                  All of these machines were three - head, which made calibration quite easy. (all pro reel to reel machines were 3 head, 3 motor)

                  I recall that all of them had either an oscillator circuit which included a "trimmer" variable capacitor which controlled the amount of erase head signal that was fed into the recording head. So, the audio signal applied to the recording head was the summation of the audio signal and the bias signal, which one could vary via the setting on the variable trimmer capacitor.

                  So, when I used to calibrate these things (according to the manufacturers specifications) I would use a known reference recording of sine wave tones (more generally, a swept sine wave with annunciation) to set up the playback circuit and then I would go after the record circuit adjustments thereafter. The record circuit was adjusted with a specific known tape type in conjunction with a variable audio oscillator in record mode while monitoring the playback circuit.

                  I recall that the bias trim cap (a screwdriver adjustable trimming capacitor which was referred to as the "bias current adjust") had a very dramatic effect on the high - end response of the tape deck. Stereo machines had two of these trimcaps, one for each channel.

                  It was not subtle.

                  And, to a lesser degree by far, it varied by tape type and manufacturer.

                  If anyone want details about how these machines were calibrated properly, let me know and I will write it up on another thread.

                  *Note: Stuarts Audio, Cranford New Jersey - - - moved to North Avenue, Westfield New Jersey while I was working there circa 1966. Wonder if they still exist ??? Great bunch of guys, I must say!! I learned a lot working there. Stuart Snowden was the principal; we had lots of fun together recording live concerts with his top - end (Magnecord Recorder- Telefunken Mic - Ampex Mixer). I still have some of those reels here today. I need to convert them to CD soon!!
                  Last edited by Craig Maier; 12-15-2006, 11:46 AM.
                  "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

                  Comment


                  • #10
                    Hey Craig - If you can post the calibration details, that would be great. This thread got me thinking that I should transfer a John Coltrane - Live in Seattle open reel tape that I got from Goodwill about 10 years ago. It's a commercial release.
                    Dan McDonald

                    Comment


                    • #11
                      Dan,

                      I will do that as soon as I get about an extra half-hour. The topic is fairly broad and needs some thought to make it universal. And of course, 'tis the season' right now so those extra moments are a bit hard to find. But, I will put it down on paper and publish it shortly.
                      "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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                      • #12
                        That's great, Craig. Take your time. Besides, the longer you wait, the longer I have til I have to find the time to do it!

                        Dan
                        Dan McDonald

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                        • #13
                          Hey Craig,
                          Just thought I'd let you know, I went to the PreSet exchange. It looks like your Stanton 500 compensation preset has the lead. More than 500 views as apposed to about 300 views on my "78" Speeds.

                          Didn't get an answer on my DC7 thought, so I thought I'd try it from this angle. Craig, what is the exact time duration of the existing Cross Fade function from start to finish? Knowing that, it would give me something to work with...

                          Comment


                          • #14
                            Hi DJ,

                            Just checked it and you are right! Interesting. I guess that a lot of folks are using the Stanton 500. I have one and I like it just because it has so many styli that I purchased over the years which work with it.

                            As for the the cross-fade time interval, it is a variable that you determine. It occurs during the highlighted portion of a file, so it can be pretty much anything.
                            Last edited by Craig Maier; 12-18-2006, 05:23 PM.
                            "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

                            Comment


                            • #15
                              Oops! I should open the User's Manual more often... I had never used the Cross Fade feature before. Looking at that window on the surface I didn't notice the ability to manipulate the length of the cross fade. I aussumed it was fixed time depending on the end of the previous selection. (Yes, I know what happens when you take the word assume apart...) Once again, oops!

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