1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Tape Biasing - Help Needed

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

  1. saemark30

    saemark30 Active Member

    Messages:
    111
    I have some EMTEC 468, is this a LN high output tape?
    What does +6dB bias refer to?
     

     

    Please register to disable this ad.

  2. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

    Messages:
    25,949
    Location:
    Athens, TN
    Emtec SM 468 is a low print mastering tape. It is lower output than the new super tapes. What kind of machine do you own? That will have a lot to do with your ability to fully make use of super tapes like the ATR, the SM 900, the old Quantegy GP9 and similar. Which are aimed at recording studio machines as a rule. Emtec 468 is an old formula from Agfa.
     
  3. saemark30

    saemark30 Active Member

    Messages:
    111
    I am running a RT-1011L.
    The 10kHz is up 3dB from the 1kHz and 100Hz signals.
    That must mean the tape is underbiased right now.
    Does EMTEC 468 work on the older machine?
     
  4. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    3db up is not drastic - but just audible
    Yes it means it is fractionally underbiased - or the eq circuits are a little out
    Most likely a bias thing.
    Sometimes a little extra at the top helps when there is a lot of treble information as that tends to 'Bias' the sound itself a little - unless you
    have Dolby HX circiuits in there as well
     
  5. ThreeOcean

    ThreeOcean New Member

    Messages:
    17
    Location:
    Philippines
    Now i know what is BIAS in tape
     
  6. jobimdream

    jobimdream Member

    Messages:
    54
    "Music is a higher revelation than all wisdom and philosophy" - Beethoven

    that is almost as awesome as this thread. you guys shred
     

     

    Please register to disable this ad.

  7. plazmaplanna

    plazmaplanna Active Member

    Messages:
    388
    Location:
    WA, USA
    My tapes are mostly Type II High Bias Cassettes

    I am Running a 3-head Denon and try to keep the sound level around +1 to +3 output

    I just recorded a couple songs though and they do not have enough bass for me.

    This tape recorder also has the MPX filter as mentioned earlier...should i keep that on? (haven't turned any filters on...but am gonna try it with Dolby C-NR and MPX)

    And with that on does that make Bias adjustment no longer relevant?

    I believe i need to turn the bias up..(have been keeping it slightly above 0 but I read that increasing it will increase bass but decrease treble....) =/

    not sure...tried to read this all and there are a lot of variables to consider...i don't have a professional measuring instrument...just the digital readout and my ears :scratch2:
     
    Last edited: Dec 13, 2013
  8. MexicoMiike

    MexicoMiike Active Member

    Messages:
    339
    Biasing a consumer deck is decidedly user-unfriendly other than with whatever bias switch might be available and which will probably not ACCURATELY adjust the bias for whatever tape you are using though maybe better than nothing. Pro (studio) decks were specifically designed for easy bias adjustment and you can set the bias for different tapes on an old Ampex 351, for example, in about 30 seconds or less per channel using the record preamp's VU meter and a signal generator.

    On a consumer deck doing it by ear with pink noise (NOT white noise) is good enough, realizing of course, that YOUR ear and the next guy's ear will be different and come up with a different bias setting. If it's your machine and will never play tapes made by others, then it doesn't matter much. But proper biasing is to ensure that any tape made by any studio would (should) play back correctly and at the proper volume on any other studio's machines.
     
    Last edited: Nov 23, 2014
  9. Geoff777

    Geoff777 Active Member

    Messages:
    174
    Location:
    Surrey England
    2 main points - Non Pro Tape machines will always compromise more and so manual Bias adjustment will very according to the user - accuracy is very difficult. My ears used to be very good and I could tune things very well by ear. I used a mixture of checks including Pink and White noise - and yes Music itself will have an effect as lots of high frequency material in a recording can actually have a small 'Biasing' effect itself which is where the Domestic system HX Pro helped as it would automatically adjust according to the music HF content
    Genuine Chrome tapes were a little bass light generally, unlike the cobalt doped Chrome setting tapes, But Chrome had superior High Frequency saturation levels over Ferric - which was generally better in the bass (hence the stab at combining them in the form of Ferrichrome)
    So - plazmaplanna - if you are using pure Chrome why not try the likes of TDK SA or Maxell UDXL11 if they are still around.
    I have not used Tape to record now for a lot of years.
     
  10. jturntable

    jturntable New Member

    Messages:
    13
    Since I couldnt comrehend the practical steps of biasing , I resorted for biasing using a white noise signal ,and then calibrating the input gain,and finally repeating the steps because it is a procedure that depends totally on hearing. I do not have specialized equipment measure distortion and such, but I got excellent results and couldnt tell source from tape,and even asked a couple of friends if tthey could hear a differnce. Very primitive ,but worked at least to my ears. What do you think ?
     
  11. vladtm

    vladtm New Member

    Messages:
    12
    Location:
    Timisoara, Romania
    Any points on how to bias a Revox B77 ? Turn the eq to the min and then start to adjust the bias, or turn eq to max, what comes first. I understand that eq is a compensation for the -6 -7 db overbias (for maxell or afga PEM), to bring the HF range back up.

    Thank you.
     

     

    Please register to disable this ad.

  12. pustelniakr

    pustelniakr Silver Miner at Large Staff Member Super Mod Moderator Subscriber

    Messages:
    7,661
    Location:
    Tucson, AZ
  13. vladtm

    vladtm New Member

    Messages:
    12
    Location:
    Timisoara, Romania
    Still one question reamins, with the record EQ pots at minimum, i cannot do the biasing using the peak-drop method, as when i turn the bias pots to minimum, the 10kz response increases and increases until i hit the limit of the pot.
    Maybe i got it wrong but i read that using 10khz to overbias, when going down, frequency increases up to a peak and then decreases when i turn the pot to minimum.

    Im my case it only decreases if i turn the pot to the maximum until it gets to 0 with the bias pot to maximum .

    I tried this on both speeds on multiple tapes, no joy. When turning the bias pot to minimum, the 10kz signal remains high.
     
  14. GPS16

    GPS16 Well-Known Member

    Messages:
    699
    Location:
    UK Manchester
    Hi Vladtm,

    I have aligned my Revox B77/A700 machines to Maxell XLI tapes. As this formulation is not listed in the spec in the manual, some adjustments were not possible. The HF Record Eq was usually the culprit. As I know the HF response is Bias dependent, if the set up spec did not work first off, I would centralise the HF Eq pots before doing setup procedure again. This at least gives you the chance that the Eq pots will be in range when you get to the HF compensation stage of the adjustments. Since I have applied this initial step, so far so good. The HF adjustment has been achieved without the pots running into the end stops.

    Bear in mind that the level at 1Khz is still going to be the reference point for level. For a first time setup on an unknown tape formulation, I would go through it once roughly to get the settings in the right ball park followed by another run through for accuracy.

    Also without wanting to state the obvious, the mechanical setup of the machine needs to be verified before the electronic alignment is considered. Without mechanical integrity the electronic alignment is a pointless exercise. A 2 head machine will allow some liberties with the end result being lost machine to machine compatibility. A 3 head machine leaves no room for errors at all.

    GPS16
     
  15. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,485
    Location:
    San Francisco

    Thanks. I'm new to tape and found the pdf quite informative. Other posts are had not quite spelled out the threshold for magnetizing the particles clearly for me and thus how the bias is helping.
     
  16. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

    Messages:
    25,949
    Location:
    Athens, TN
    They don't for older consumer recorders which can barely bias the likes of Scotch Dynarange or Maxell UD at best. Today's tapes demand more than Maxell XL1 at that bias wise. Simple fact of life. Many an older Akai, Sony and their ilk have those limitations into the late 1960's. A Crown or a ReVox are exempt and the studio machines.
     

     

    Please register to disable this ad.

  17. cferry1

    cferry1 Member

    Messages:
    94
    dr*audio's reply above Jan. 6, 2010 - I believe is a a very good description of tape deck tape biasing and adjustment !
     
  18. Wilhem

    Wilhem Active Member

    Messages:
    328
    If the bias signal is too low, the highs will be accentuated and you will get higher distortion. The method of adjusting the bias is to record a 1KHz tone and a 10KHz tone at -20dB (so you will not saturate the tape and lose highs) and adjust the bias so that they are equal on playback.

    This explanation is inaccurate. Too much bias current does tend to increase the erasure of short wavelengths because the ratio of audio and bias is too great in favor of the bias signal, but the short wavelengths are also driven into the coating and away from the surface of the tape. That's why the high frequencies decrease. Too little bias brings the short wavelengths and long wavelengths to the surface, but there is not enough depth to the long wavelengths to provide output and too little force to activate more particles. That is the cause of the distortion. Bias is set by selecting a frequency, often recommended by the tape manufacturer, and increasing the bias current until the output at the operating level peaks and decreases by the recommended amount. The data sheet for the tape will display the trade-offs in terms of distortion and MOL/SOL. Then the record EQ is altered to guarantee flat frequency response at a level 20 dB below the operating level. Bias is the method to control output and distortion. Although it is also a factor in terms of frequency response, the correct technical method to ensure flat frequency response is record EQ.
     
  19. Artie

    Artie AK Subscriber Subscriber

    Messages:
    1,830
    Location:
    Jax, Fl
    I hope no one minds if I throw my 2-cents worth in here. The explanation of tape bias always seems to get too technical. It really isn't.
    Anyone remember the old days, in science class, where you'd sprinkle iron filings on a piece of paper. Hold it over a magnet. Then tap on the paper. The iron filings would align themselves with the magnetic lines of force. You could actually "see" them. (The lines of force.)

    If we apply this analogy to tape bias, the paper is the polyester backing of the tape. The iron filings are the magnetic coating of the polyester. The magnet is the recording head. The magnetism is the audio signal. Which brings us to the "tapping" on the paper. That's the bias. You excite the medium so the magnetic particles "dance" to the music. Tap too hard, and you scramble everything. Tap too light, weak signal.

    Now, move the paper away from the magnet, and tap again. You've "erased" the signal. The bias is the same signal used to erase, but lighter.

    Like I said. My 2-cents worth. :)
     
  20. allanmatters

    allanmatters Active Member

    Messages:
    231
    Location:
    Bahrain, Al Manama
    I found it . It was one of the potentiometer s . I adjusted them accordingly (decreased it , mostly made them equal as one of them was more ) and the faint electric sound has gone . It's slightly present like 1 ℅ ,only occurs at very harsh instrumental effects like example I was playing a Fleetwood Mac track it was more occasional there put not as much present as in before I had adjusted the potentiometer s . So far so good .feels 98% right . I don't mind the extra 2%
    The deck sounds excellent with the stock super aurex head .
    Took some pics if it could help any one in the future
    Thank you to all who have helped me .
    Appreciate it . I love audiokarma!
     

    Attached Files:

Share This Page