2 questions

[antispatula]

1. I'm having a fun time figuring out adjusting the record bias.......So let me get this straight: It's a really high freq. (in the 100kHz range?) that is mixed in with the audio signal that kind of "loosens up" the magnetic particles on the tape so they can be arragned into the what the audio signal is? SOMETHING like that. And channel 1 on my machine sounds great when I record stuff on it, but not when I playback a recorded tone that is a high frequency. It is weak, and it sounds......grumbly. As if you can hear rocks tumbling down a hill. This is a very very soft sound, but is there. This has to do with the record bias level I'm assuming? And what is bias trap?

2. My near-brand-new MRL tape has print-through problems. Like when it says "1 kilahertz tone, fringing compinsated" then plays the tone, I can hear the guys voice a few times after he finished saying it, like an echo. Is this normal to have such obviouse print-though?

 

[FALKEN]

is your tape old?

have you gotten to the part where you adjust the eq?

 

[Muckelroy]

Bias fixes a problem that is sometimes known as "zero crossing" distortion. If you record onto magnetic tape WITHOUT a bias, you will get something terribly different from your origginal signal. (I'm talking, like eggs frying, 1950's telephone distortion!)

I assume you know what a sine wave looks like.
If you record a sine wave w/out bias, the parts of the sine wave that are close to the zero Y-axis (near the "zero crossinggs") will flatten out verically, and become MUCH steeper than normal. (if you can visualize it.) Due to the nature of the magnetic particles, the parts of the signal that have a small amount of signal get cancelled out by the adjacent strongg magnetic signals. Long story. Anyway, hope that sort of describes it. YOU GET BAD DISTORTION!!

So to fix it, we minimize the amount of time that the signal has to spend near the zero crossing. (like, on a sine wave, the parts that are close to zero.) We do this by mixing the input signal with a VERY HIGH FREQUENCY called "bias." On pro decks, this frequency is about 150 kilohertz.

This way, the signal is constantly moving up and down in amplitude, REALLY FAST, while simultaneously moving up and down with the signal of the music. For a visual comparison, it's like a regular sine wave that still moves up and down normally, but it's drawn with a scribbly, hairy line instead of a straight, smoothe line.

Thus, distortion is brought down to a minimum. As for how to fix your particular machine. sometimes you just have to use trial and error. Finding the right AMPLITUDE for your bias signal may require some fishing. Just throw on a blank tape, and (if you have a 3-head machine) record music, er, whatever, while monitoring from your repro head. Tweak the bias around until you get a desireable amount (that means a REALLY MINIMAL AMOUNT) of distortion. You may not even realize that what you're hearing is distortion. It may be such a small amount of distortion, that it alters small ranges of frequencies. So just tweak it till it sounds RIGHT to you.

OR, be technical, and follow the over-biassing procedure for your particular tape, and your particular machine. This topic shouldn't be hard to find on the forum. I'm tired of typing, so good luck!

-callie-