Noise Reduction for Reel to Reel

[DonH50]

Thanks very much Roger! I also downloaded the paper. - Don

 

[Mark (Basspig) Weiss]

Dolby B and its ilk generally boost the highs during recording to get them further above the HF noise ("hiss") floor. So, to play back a Dolby B (etc.) recording on a non-Dolby deck all you usually need to do is turn down the treble a bit.

Dolby B is a HF compander system, so it's much more complicated than turning down the treble. What you'll end up with is constricted HF dynamics, even if the low level sounds natural. It's not the same as FM preemphasis where you have a constant 75uS curve at all modulation levels. Dolby B adds more treble down near the noise floor and adds nothing up near 0VU. Dolby B tapes MUST be played back on a Dolby B decoder, or the HF dynamics won't be even close to correct.

 

[DonH50]

Hi Mark,

Yes, of course you are right (as implicit in the previous posts between Roger and I), but the question was what to do with a Dolby recording when one does not have a decoder. IME, turning down the treble will make the recording playable, albeit without the dynamics. I should have left off "and its ilk" as all the other formats I have tried are more aggressive and suffer much more from the lack of a decoder; Dolby B is the only flavor that has provided "acceptable" (yes, highly debatable!) results. Probably for the reasons Roger mentioned -- it targets a medium without a lot of dynamic range to begin with so is less aggressive than the other algorithms.

My memory of Dolby systems is very old and vague after so many years so I must withdraw out of respect to you who know better. Too many mistakes in one thread for (by) me! I do appreciate the opportunity to (try to) keep up with the newer systems. I was trying to remember what the various RR and cassette units I owned and used through the years had on them, but it's a lost cause. I do know I never really liked C but am not quite sure why after all this time...

Thanks for the information,
Don

 

[naturephoto1]

I am considering getting this Advent 101 that is functioning but the meter is stuck. It really needs to be cleaned up and the switches need to be lubed, but the Advents were known for good sound. I am sure that the calibration reel and cassette are not included. I would only plan on using this for playback of Dolby B prepared R2R tapes and not to make recordings. Please do not try to outbid on this unit, I would appreciate it.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190562538819&ssPageName=STRK:MEWAX:IT

Rich

 

[naturephoto1]

As an update, I did not purchase the Advent 101 that was on ebay. Wayne Gunn, who is building my upgraded hybrid Amplex 440C/B R2R tape deck has an Advent 100 Dolby B unit that he has had in storage. He is checking the unit out for condition and functionality. It it checks out, I will get this from Wayne and I will have him include the Advent when the Ampex ships presumably this coming Friday, August 19.

Rich

 

[naturephoto1]

Unfortunately the Advent 101 Dolby B Noise Reduction that Wayne had was not functioning. However, I purchased/won this one on Ebay that is supposed to be delivered on this coming Monday; according to the seller the unit is functioning properly as are the meters (no calibration tape however).

http://www.ebay.com/itm/190586346384?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I will report in after it arrives and let everyone if it appears to functioning properly. If so, I will post photos.

Rich

 

[Steve williams]

Rich

why are you trying to complicate things

 

[naturephoto1]

Rich

why are you trying to complicate things

Hi Steve,

Because I have some Dolby B pre-recorded tapes that sound a bit bright. I only plan to normally use the Advent with Dolby B encoded tapes; in fact I only intend to run the cabling through Advent for the Dolby B tapes. Otherwise, just the "naked" upgraded hybrid Ampex 440C/B R2R tape deck and the Advent will be turned off (the normal/usual state of affairs).

Additionally, as Charles (Stellavox) had indicted in the thread that I started regarding the Art Garfunkel Watermark Album side 1 Mastertape that I had won on Ebay, there is a steady test tone at the beginning of the 1st of the 2 Yes tapes that I just won: Best of the Biscuit Yes Live in Los Angeles:

http://www.ebay.com/itm/160662568603?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

So, according to Charles, the Yes Concert Tape should be a Dolby B encoded tape.

Rich

 

[naturephoto1]

Well the Advent 100 Dolby B Noise Reduction unit arrived today. I am not sure if it is working properly and I can't get the meter test to work all the time. But, from what the sender indicated the unit works. The problem is that the machine has older RCA connectors which are too close together for my much newer high end RCA ICs with the screw type locking ends. So, I probably will not use the unit even if it works at this point. Of course the unit could be modded to have greater distance between the left and right channels for the RCA connectors. I will have to think this through more. If I don't use it I will have to accept the sound of some of the Dolby B recordings without the Noise Reduction.

Rich

 

[mep]

If I don't use it I will have to accept the sound of some of the Dolby B recordings without the Noise Reduction.

Rich

Rich-Those tapes won't sound right if they are encoded with Dolby B and you play them back straight without it. Since the Advent isn't high on collector's lists, I would modify the unit and space the jacks apart. You may want to try it first with a cheap pair of ICs and make sure it works first.

 

[c1ferrari]

Somewhat of a similar predicament

If I don't use it I will have to accept the sound of some of the Dolby B recordings without the Noise Reduction.
Rich

here, Rich. I need to research and source a Dolby A and/or Dolby SR unit. My nascent understanding is that these units are "companders" and influence more than "tone".

Good luck with everything

 

[RogerD]

Well the Advent 100 Dolby B Noise Reduction unit arrived today. I am not sure if it is working properly and I can't get the meter test to work all the time. But, from what the sender indicated the unit works. The problem is that the machine has older RCA connectors which are too close together for my much newer high end RCA ICs with the screw type locking ends. So, I probably will not use the unit even if it works at this point. Of course the unit could be modded to have greater distance between the left and right channels for the RCA connectors. I will have to think this through more. If I don't use it I will have to accept the sound of some of the Dolby B recordings without the Noise Reduction.

Rich

Rich,

You have your core cables in place. Running std grade IC's with your dolby unit won't degrade the sound. If you have a set of monster,mogami or other cables with std ends try that,it will sound fine. If there is any degradation it will be possibly from the dolby unit itself(maybe).

 

[naturephoto1]

Rich-Those tapes won't sound right if they are encoded with Dolby B and you play them back straight without it. Since the Advent isn't high on collector's lists, I would modify the unit and space the jacks apart. You may want to try it first with a cheap pair of ICs and make sure it works first.

here, Rich. I need to research and source a Dolby A and/or Dolby SR unit. My nascent understanding is that these units are "companders" and influence more than "tone".

Good luck with everything

Rich,

You have your core cables in place. Running std grade IC's with your dolby unit won't degrade the sound. If you have a set of monster,mogami or other cables with std ends try that,it will sound fine. If there is any degradation it will be possibly from the dolby unit itself(maybe).

Hi Guys,

Thanks for the suggestions. I have hooked up the Advent 100 Dolby B Noise Reduction unit with it sitting on top of some Herbies Tenderfeet between it and my upgraded NuForce Oppo 83SE to test it and to protect the units. I found a couple of pair of throwaway cheap RCAs with smaller connectors. I don't have a calibrations tape, and as a result I am having to quickly adjust the unit by ear. But, it seems that the Advent is in fact operating properly. I am listening to the 4 track Blue Jays 7 1/2 IPS R2R tape by Justin Hayward and John Lodge. The meters are functioning properly. I had a glitch a few times for a few minutes when things didn't sound right. I was getting a high pitched whine coming out the speakers. I am not sure of the problem. But, I rewound the tape and things improved. I am not quite sure what happened, but I adjusted the output of the Advent after running the tape back. I am not sure if it is the tape, it is wound too tight or the Advent.

I am going to try side 2 now. I am not noticing the relatively painful highs that I heard on the tape initially though.

I will have to decide what to do regarding ICs (I am not sure what I have at this point for old cables and where they are). I know that I have some older Monsters and others but since we moved I will have to look around. Of course, I may have the RCA inputs and outputs changed as Mark has suggested.

Rich

 

[RogerD]

Hi Guys,

Thanks for the suggestions. I have hooked up the Advent 100 Dolby B Noise Reduction unit with it sitting on top of some Herbies Tenderfeet between it and my upgraded NuForce Oppo 83SE to test it and to protect the units. I found a couple of pair of throwaway cheap RCAs with smaller connectors. I don't have a calibrations tape, and as a result I am having to quickly adjust the unit by ear. But, it seems that the Advent is in fact operating properly. I am listening to the 4 track Blue Jays 7 1/2 IPS R2R tape by Justin Hayward and John Lodge. The meters are functioning properly. I had a glitch a few times for a few minutes when things didn't sound right. I was getting a high pitched whine coming out the speakers. I am not sure of the problem. But, I rewound the tape and things improved. I am not quite sure what happened, but I adjusted the output of the Advent after running the tape back. I am not sure if it is the tape, it is wound too tight or the Advent.

I am going to try side 2 now. I am not noticing the relatively painful highs that I heard on the tape initially though.

I will have to decide what to do regarding ICs (I am not sure what I have at this point for old cables and where they are). I know that I have some older Monsters and others but since we moved I will have to look around. Of course, I may have the RCA inputs and outputs changed as Mark has suggested.

Rich

Hi Rich,

Another tidbit I'll throw out there is the BG caps are famous for having a edge in the top end for about the first 50 to 75 hours. Also that Lundahl will take a while to smooth out but that should happen quickly,fwiw. you might try to experiment with the level on the Ampex and see if there is any change up or down.

 

[naturephoto1]

Okay guys. I am open to suggestions. I dug up an old pair of Audioquest Ruby RCA ICs and 2 pair of Monster IC cables. Someplace there are some 1/2m Audioquest Laps X3 (as I recall) RCA ICs, but I think that they probably have the same connectors as the Audioquest Rubys. In any case, the Rubys don't fit the Advent, they are too big as is 1 pair of the Monster RCA ICs. The other pair of Monster RCA ICs are pushing the connections.

Should I have a tech replace the RCA inputs and outputs f the Advent 100 to take the better IC cables such as those that I already have or use really inexpensive RCA IC cables and/or the Monster cables? I am concerned that the I will lose performance using the inexpensive RCA IC cables.

Rich

 

[RogerD]

Okay guys. I am open to suggestions. I dug up an old pair of Audioquest Ruby RCA ICs and 2 pair of Monster IC cables. Someplace there are some 1/2m Audioquest Laps X3 (as I recall) RCA ICs, but I think that they probably have the same connectors as the Audioquest Rubys. In any case, the Rubys don't fit the Advent, they are too big as is 1 pair of the Monster RCA ICs. The other pair of Monster RCA ICs are pushing the connections.

Should I have a tech replace the RCA inputs and outputs f the Advent 100 to take the better IC cables such as those that I already have or use really inexpensive RCA IC cables and/or the Monster cables? I am concerned that the I will lose performance using the inexpensive RCA IC cables.

Rich

Rich,

Dave Dintenfass made me a pair of cables using plain old microphone cable with the cheapest soldered ends I have seen,the perfect anti cable. I use them on my 350's and they sound great. Try the monsters and see what happens.

 

[DonH50]

I do not know the output impedance of the Dolby unit. I would not use the cheapest cables, though it might not matter; my default with unknown gear is to use low-capacitance cable and be done with it. Microphone cable is usually a good choice.

 

[naturephoto1]

I do not know the output impedance of the Dolby unit. I would not use the cheapest cables, though it might not matter; my default with unknown gear is to use low-capacitance cable and be done with it. Microphone cable is usually a good choice.

Hi Don,

According to the Advent 100 Manual, outputs (after Dolby calibration) (I don't know if not calibrated) with the Dolby Level controls at maximum from Dolby Level (0 VU tape level) output is 1.0 volts at less than 1000 ohms output impedance.

Rich

 

[DonH50]

Typical cables run ~20 - 30 pF/foot, so a 6' cable is about 180 pF'ish max. Call it 250 pF, then 1000 ohms yields over 600 kHz bandwidth if treated as a lump sum. You should be OK with any reasonable cable, at least as far as bandwidth is concerned. There are all the usual other cable considerations, natch.

Dolby cal should affect the response curve and amplitude levels, no impact on cable choice.

 

[stellavox]

Hi Gentlemen (are there lady tapesters anywhere?),

I just posted some info on my Dolby A experiences on the Tape Project forum. Figured I'd save you'all the technobabble on this really hot and uncomfortable day.

However, if you do (continue) to collect Masters? (Mile's Safeties?) you will inevitably run into Dolby A encoded tapes and will need the appropriate decoder. I've had a lot of experience with them but don't want to "clog" things here.

AND, I understand that there are a number of really good sounding Dolby B encoded 4-tracks (Barclay Crocker - sp?) out there. Decoding them to capture their best sound is another story.

Cheers

Charles