Tape Biasing - Help Needed

Discussion in 'Tape' started by Bigerik, Jan 6, 2010.

  1. KristianJ

    KristianJ Hillman owner

    Messages:
    124
    Location:
    Skåne, Sweden
    Thanks, that settles it !!
     

     

    Please register to disable this ad.

  2. mjolley

    mjolley Going Nowhere Slow

    Messages:
    90
    Location:
    Louisville, KY
    I've read though this thread so I don't think this was mentioned but there's so much good information in here forgive me if I'm being redundant but this could be useful...Your deck was probably set up to be biased for one of the tape types popular when it was released. The service manual/users manual may tell you what these tapes are.

    My Onkyo Integra TA-207's service manual states the blank tapes to be used for testing are UD-1 (Type I), XL-II (Type II) and XS (Type IV). So, assuming the deck hasn't drifted from the time it was made, a Maxell XL-II would be the best responding high bias tape, assuming you don't adjust the bias manually. They don't specify the manufacturer but I know XL-II is Maxell and so is UD (I believe), but all the Maxell metal tapes I've gotten have been desginated MX.
     
  3. fortycoats

    fortycoats Super Member

    Messages:
    1,286
    I agree. I have a Teac A-3440 and my recent-ish (EMTEC) tape stock is supposedly a +6 tape. The 3440 won't go +6.
     
  4. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    Playback on Cassette tapes has 2 eq settings usually
    120µs (brighter with a little more hiss)
    70µs ( slightly mellower with less hiss)
    Ferric tapes have less top end headroom and therefor
    use a slightly brighter playback eq to get the best out of them.
    Chrome, Ferrichrome and Metal all use the 70µs eq.
    Ferric tapes are lowest in the bias range a figure of 80 - 120 springs
    to mind- but I admit I have forgotten what that stood for - except
    for a level of Bias
    Chrome were typically in the region of 150
    (Some Chromes could get away with high normal bias)
    Metal is way higher!
    Ferrichrome was an oddball - in order to try to get the best of both worlds
    where Ferric had good bass and 'true Chrome' had good treble -
    a combination of the two was mad in the form of ferrichrome
    this required a similar bias to normal - maybe slightly higher - but
    the result was - good bass and good treble and a bit of presence mid suckout
    SO
    they made a special record eq adjustment to slightly boost the mid presence
    on some machines.
    (There were a several Cobalt Chroime tapes manufactured which overcame the
    inherent bass weekness of true Chrome.)
    The Pioneer CT-F650 was one such machine (I also had one many years back)
    With carefull adjustments the CT-F650 was awesome!!
    I was only upset that you were stuck with the MPX filter if you used DolbyB
    (19Khz).
    HX Pro was a clever idea
    If the music was quite dynamic and contained bursts of lots of treble that treble could
    effectively temporarily 'Bias' the recording - resulting in an apparent momentry dulling
    of the top end - usually attributred to overload.
    HX pro monitored the music content and when lots of HF was present it would
    reduce the bias to compensate - then return it immediatly after.
    The rec level calibration is also very important - particularly if using a noise reduction.
    Noise reduction is a companding system where at low levels it will boost higher
    frequencies and at high level it won't. On playback it would do the reverse.
    So you can see it is critical to match record and playback. otherwise a pumping effect may be heard
    - or at least a loss of HF detail and quality.
    3 head machines made it a little easier to get the best results
    I would record white or pink noise and directly compare record and playback whilst
    fine tuning Bias and levels.
    With a 2 head it was a longer process of trial and error.
    My ears were very good when I was younger and I managed to replace the heads
    and setup the CT-F650 entirely by ear - including L&R channels balance internally.
    It was very rewarding - all of this is an art that is dying with the digital age
     
    Last edited: Mar 9, 2011
  5. luddite

    luddite Super Member

    Messages:
    1,156
    For those of you who have real experience in setting the bias to your own satisfaction, did you eventually find any significant difference between setting the bias by ear and setting it by technical protocols?
     
  6. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    I always did it by ear - I found I got better more accurate results.
    Usually I would initially use a recording of White noise from HFS 75
    It was much easier and quicker with 3 head machines.
    Using a Sony (can't remember model number now~TC-K 600?) with built in calibration tones and using the rec level bars - I found despite getting both levels (low and high) the same - I could get a gnat's whisker better sound by further fine tuning by ear.
    After using white noise - I would also check with the music - if there was a lot of HF in the music it might need a tiny bit less bias.
    (Hope some of my ramblings are helpfull)
    :thmbsp:
     

     

    Please register to disable this ad.

  7. fortycoats

    fortycoats Super Member

    Messages:
    1,286
    I have a TC-KE600S and a TC-KE500S, both of which have the "auto" calibration feature. I find the auto level recommendations on both of them are off. That is "off" as far as my ears are concerned, much like what you're experiencing. It probably actually is what follows "protocol" but that's not the same as satisfying your ears. "Protocol" states that least distortion of the bass tones comes at a bias level 2 or 3 dB (or whatever, depending on the tape) below what gives highest treble response, and that the correct bias level is therefore a compromise between the two and the "best" bias level is roughly half way between them. In real life, most people adjust bias for best treble response and most people find that they can't hear whatever tiny amount of bass distortion that might result, if any. Basically, adjust it so that the output sounds as close to the source as possible.
     
  8. flavio81

    flavio81 Turntable technician

    Messages:
    2,558
    Location:
    Lima, Peru
    Wonderful attachment. Thank you very, very much.
     
  9. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    IMHO manual adjustment using your ears is best.
    Although what program material to use??
    I used to do multiple tests prior to actually recording
    1st I would use white noise at -20db
    much easier BTW with a 3 - head machine - much slower process otherwise!
    Next I would do the same actually at 0db - bear in mind the HF will start to get
    saturated and therefore it's a matter of diddling around - with some machines it maybe decided that testing at -10db is optimum
    After that I would sample some music to see how that sounds
    Bear in mind as I mentioned before - music with a lot of HF content will effectively 'bias' the tape a little.
    If you are recording from a record or CD (for personal use of course!) - then you can do a sample recording once you are pretty close

    Pink noise is also pretty good as it has all the frequencies - just less top and more bottom and therfor closer to normal music program material
     
  10. goldear

    goldear Certifiable Audio Junkie

    Messages:
    8,435
    Location:
    Seattle
    Interesting info. Thanks again Wilhelm!
     
  11. Mehul

    Mehul New Member

    Messages:
    4
    So is it possible to alter the the bias (internally) on a deck with HX-Pro?
     

     

    Please register to disable this ad.

  12. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    Yes absolutely.
    The adjustment pot will be inside, usually, the basic adjustment can be made just the same.
    My old Denon DRM-34 Decks have fine tuning on the outside for Bias and Level, and also inside -
    incidentally some decks have seperate left and right inside as well. They are HX Pro decks.
    The HX pro will operate as well, but kind of seperately to the Bias pots
    like another adjustment in series with the Bias pots.
    :thmbsp:
     
  13. Mehul

    Mehul New Member

    Messages:
    4
    Thanks for your reply Geoff! :thmbsp:

    I had just purchased a Denon cassette deck (DRM710) and following your reply I decided to open it up and check this out, and yes you are absolutely right.

    As you were saying I found that the Denon DRM710 actually has separate bias pots for the left & right channel. I found the pots only needed slight adjustment to the default settings for getting better highs on normal type cassettes.

    The deck also has a fine tuning adjustment on the outside so I adjusted it so that I get the best sound when it's in the middle, which should avoid another internal adjustment.

    On another point, I found this deck is a little lacking when it comes to recording bass, do you know if this can be adjusted manually inside?
     
  14. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    I am suprised to hear that about the Bass :scratch2:
    I would try doing all my bias test with the Dolby off first
    Does the 710 have a 'Level' pot on the outside??
    It is just concievable the Dolbly 'Level' is off and you have compensated with
    the Bias (not very likely- but just possible)
    If there is no pot on the outside - there will be one inside - I think this one only has fine Bias control (not talking about the output level)
    Level was for making sure the Dolby tracked correctly as it is important
    that the internal playback and record levels match so the Dolby variable curve
    Matched record and playback.

    Anyway - that thought aside - usually Bass would only suffer if the Bias was too low - and you would get too much treble.
    If the head has become magnetised that maybe affecting the sound (usually makes it more muffled though)
    So I would try deguasing the tape heads - this is like randon posative and negative magnetism pulses that get rid of any residual magnetism in the heads - could be they need this - you used to be able to get a TDK tape shaped one which was the easiest to use.

    Try all these things and see if anything helps :thmbsp:
     
  15. Mehul

    Mehul New Member

    Messages:
    4
    Thanks for your reply Geoff.

    I carried out some more tests and compared recordings with my other deck (Teac W865R) and as you had suggested I had set the bias ever so slightly high. I've slightly tweaked it and all seems to be well. :thmbsp: I guess it's all about getting the right balance between bass and treble response.... and never expecting recordings to sound 100% identical to the CD!!

    Thanks again for your help and advice, it's much appreciated :tresbon:
     
  16. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    Glad to hear
    To be honest it is a bit of an art getting it right. If you are as OCD as
    I can be at times - then it becomes easier after the first 50 times! LOL
    Seriously - my ears used to be hyper sensitive, so I am sure that made it easier. I don't use my tape decks for recording these days so I am sure
    I would find it takes longer now. Trial and error on practice times before
    making your actual recording - always a good idea.
    :thmbsp:
     

     

    Please register to disable this ad.

  17. Wilhem

    Wilhem Active Member

    Messages:
    324
    Consumer Explanation of Bias

    The attached file comes from Mr. O'Kelly who was asked for smaller files of his material. This bulletin also appears to have some revisions in it, too. I have received new versions on EQ, reading meters, the cassette housing, and chromium dioxide. The work on flash memory, optical discs, and hard drives are file sizes that are too big to post, unfortunately. The bulletins on print-through, video transmission, and video recording are still missing.

    I'm posting this because this thread is a sticky, and the question of what bias is and what it does always comes up. These were bulletins for interested consumers, so they do not have the mathematics that would make a head swim trying to decipher the formulations.
     

    Attached Files:

    • Bias.pdf
      File size:
      663.1 KB
      Views:
      128
    smurfer77 likes this.
  18. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    Almost always better by ear.. :)
     
  19. SoNic67

    SoNic67 Well-Known Member

    Messages:
    919
    There are ways to modulate the bias level during recording to compensate for higher level of trebles in the music. Dolby HX Pro was doing that using the Dolby B detector, but there where other systems on the same concept.
    I did build one in the 80's based on a schematic drawn by me. A FET was used to "shunt" some of the bias when the music had lots of HF.
    Adjusted by ear first and finally with a scope to minimize the LF distortions.
     
  20. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    Sounds great, if you will pardon the pun!
    The concept of variable fine bias depending on HF content seems
    to work well. Otherwise the sound can seem to 'thicken up' whenever there are crashing symbles or lots of HF content generally.
    Some Cassete decks had a sperately switchable MPX filter which filtered at 19khz
    Some people reckoned it sounded better when that was in - it was orignally
    intended to filter out the Multiplex filter for FM transmission - but also helped
    out with extra high frequencies most of which you couldn't hear - which might be adding 'Bias' to the tape recording.
    I used to be able to hear the effect of that switching in and out!!
    (alas no more!)
     

Share This Page