Quick Bias Question

[sackbutcharlie]

I would appreciate any input on the following item.

I have read a little bit about bias and have a general idea what it does. But what I can't quite figure out is this:

On a 4 or 8 track, does the bias get laid down across all tracks even if only recording on one? So if I do 8 tracks, one at a time, Is bias laid down 8 times across the entire tape or just once on each track as that track is recorded? And then is it laid down across the entire tape every time I bounce, or just to the tracks that are recording? And should I even be concerned? How much noise does bias create?

ALSO... I am new to the BBS here. If this type of question is more appropriate to the "Newbie" forum, please let me know.

Thanks!

 

[regebro]

It's only done on the track you record.

It adds no noise. What is does is that by applying a high frequency signal it constantly makes sure that the tape is operating outside the hysteresis of the magnetic material, thus ensuring a linear transfer function.

In short: It sounds better.

 

[The Ghost of FM]

Biasing a tape when recording essentially warms up the tape so that a recording can be made that is free of excessive noise and distortion.

Think of it as you would like plying a women with soft candle light, the right music, small talk and foreplay before you do the deed. It makes thing go smoothly and to your liking.

Cheers!

 

[regebro]

Interesting way of explaining hysteresis.

 

[sackbutcharlie]

WOW. Women, candlelight, now I know why analog sounds better!

Thanks!

 

[regebro]

Digital is like a man. Straight, honest and always ready.

 

[The Ghost of FM]

Digital is like a man. Straight, honest and always ready.

It is?

I always thought of digital as a bunch of ones and zeros?

To each his own, I suppose.

Cheers!

 

[regebro]

Exactly. Full speed ahead or doing nothing at all. Typical manly. None of that female "mmmmaybe" fuzzy stuff.

Either on or off.

 

[DigitalSmigital]

Think of it as you would like plying a women with soft candle light, the right music, small talk and foreplay before you do the deed. It makes thing go smoothly and to your liking.

Cheers!

Ask him about headroom. That one is my favorite. Go ahead. Ask him.

 

[acorec]

It's only done on the track you record.

It adds no noise. What is does is that by applying a high frequency signal it constantly makes sure that the tape is operating outside the hysteresis of the magnetic material, thus ensuring a linear transfer function.

In short: It sounds better.

Biasing in Tape Recording
A music signal alone cannot be used to produce a faithful tape recording of a sound because the magnetization of the tape is so sensitive to its previous magnetic history, even the effects of the signal recorded just ahead of it. A high frequency bias signal is typically applied to the tape through the tape head along with the music signal to remove the effects of this magnetic history. This large bias signal (typically 40 to 150 kHz in frequency) keeps "stirring" the magnetization so that each signal to be recorded encounters the same magnetic starting conditions. The necessity for biasing has its origin in the magnetic property called hysteresis - the magnetic material tends to hold onto any magnetization it receives and must be actively driven back to zero to start over. Magnetic emulsions made with chromium dioxide require a larger biasing signal to make use of their wider dynamic range, so modern recorders have different bias settings for iron oxide, chromium dioxide, and metal tapes. With optimum biasing, the recorded magnetic image is proportional to the signal current applied to the record head.



Hysteresis
When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. It must be driven back to zero by a field in the opposite direction. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again. This property of ferrromagnetic materials is useful as a magnetic "memory". Some compositions of ferromagnetic materials will retain an imposed magnetization indefinitely and are useful as "permanent magnets". The magnetic memory aspects of iron and chromium oxides make them useful in audio tape recording and for the magnetic storage of data on computer disks.

 

[sackbutcharlie]

Thanks for the excellent explaination!