For the most accurate alignment, most manufacturers of tape recommend that you use a test frequency of 10 kHz and overbias (increase the bias levels until the playback output drops) by a certain number of dB. The usual speed given in the recommendation is 15 ips; if you were using 30 ips, either the test frequency or the amount of overbias had to be changed. For most machines the manufacturers recommend a 3 dB overbias at 15 ips.

When this method was put to practice, it had a few flaws, especially to the student or new recording engineer.

The recommendation didn't work well for all machines, just the majority. If the gap width of your tape machine was a little bit different, you had to use a different amount of overbias. The tape and tape machine manufacturers did publish data on this, but you had to realize your machine was different. An older Otari MX 50-50 machine, for instance, can't even be aligned using the "overbias 10 kHz by 3 dB" method

2. Overbiasing by 3 dB is a cumbersome method procedure when a recording engineer (or the assistant) is trying to align a machine just before a session. It can be done, but takes time and care. Many new recording engineers, especially under the pressure of getting a session underway, would miss the very narrow peak output at 10 kHz and mis-align the machine. Using 10 kHz , the bias adjust control has a "hair-trigger" action and extra care must be made that you are on the peak before you overbias 3dB. This involves slowly moving the control, when the client and the studio manager is saying "hurry up." Under these circumstances I have seen seasoned engineers who have aligned machines hundreds of times, misalign the machine.

Tape manufacturers have come out with new tape formulations that offer the possibility of a high operating level with less noise and distortion results and less overload of the extreme highs. With these new tapes the recommended overbias at 10 kHz is different for different brands of tapes. Also the gap width on the heads makes a bigger difference. This means that the recording engineer has to keep different factors in mind to follow the recommendations (including tape speed, the brand of tape and the gap width on the machine being used). Fortunately there is a better way.

There is a universal method of setting bias that works well for different types of tape and works equally as well on almost all machines. The result are close enough at 15 ips and 30 ips that you can use the same method at both speeds. In practice it is just about as accurate as the manufacturer's recommendations and allows the bias adjust and record level to be done in one step (in half the time).

The method is simple. While recording a 0 dB test frequency of 1 kHz and watching the playback, overbias by 0.2 dB (2/10 of a dB). This means that you turn the bias control slowly up (from counter clockwise) until the level "peaks" and continue turning it clockwise until the level drops 2/10 dB. Its as simple as that. Next your screwdriver goes over to trim the record level control - almost like one step.