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Tape Tech / Re: What are the effects of bias current?
« on: November 20, 2008, 11:12:16 PM »
I thought this thread had been pretty well covered, until I came across what I've pasted in below. It's a direct quote from the bottom of page 11 of the MRL paper "Choosing and Using MRL Calibration Tapes for Audio Tape Recorder Standardization". (http://home.flash.net/~mrltapes/choo&u.pdf), one of my favorite papers to read. (I guess I should read it more often, since I had forgotten about this). The paper is a dandy, since it's written in a language that I can understand, and completely explains levels, eq, and more. The paragraph below prescribes a method of biasing for anyone (besides myself) who still is unsure of where to set the bias point when using an unfamiliar tape. I can't wait to try it. Read the whole paragraph- the best part comes at the end!
"An old, simple, and effective method that we use for setting bias with all kinds of tape is to use a 1000 Hz test signal. First set the bias current for maximum recording sensitivity. Then, for 15- and 30-in/s recording, increase the bias current so that the recording sensitivity drops by 0.2 dB. For 3.75- and 7.5 in/s recording decrease the bias current so that the recording sensitivity drops by 0.1 to 0.2 dB. Another method, recommended by tape manufacturers, uses a 10 kHz test signal. We find this method more complicated ? you need toknow the gap length of the recording head, and the amount of signal reduction for each kind of tape and each speed ? and without any redeeming social value."
"An old, simple, and effective method that we use for setting bias with all kinds of tape is to use a 1000 Hz test signal. First set the bias current for maximum recording sensitivity. Then, for 15- and 30-in/s recording, increase the bias current so that the recording sensitivity drops by 0.2 dB. For 3.75- and 7.5 in/s recording decrease the bias current so that the recording sensitivity drops by 0.1 to 0.2 dB. Another method, recommended by tape manufacturers, uses a 10 kHz test signal. We find this method more complicated ? you need toknow the gap length of the recording head, and the amount of signal reduction for each kind of tape and each speed ? and without any redeeming social value."