Head Azimuth Alignment
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transmitter
This Is Mostly Likely An AM Broadcast Transmitter.
Note What Looks Like An Universal Audio 175 Compressor/Limiter On The Left.

Overview

  • Azimuth

    Azimuth is defined as the left/right movement of an audio head, as seen from the front. This is designed to align all of the head gaps exactly perpendicular to the tape. Typically, azimuth is performed in one of two ways, the oscilloscope method, or the summing method. Both methods are quite effective, and both have their advantages over the other.

  • Oscilloscope Method

    In this case, an oscilloscope is used in the X-Y mode. The two scope inputs come from two tracks of the tape machine. The ideal tracks to use should be as far apart as possible to allow for greatest resolution. On a 24 track machine, however, typically tracks 2 and 23 are used since the outside tracks (1 and 24) are susceptible to high frequency loss. During playback, if the head is perfectly perpendicular to the tape, the waveform seen on the scope will be a straight 45º diagonal line from lower left to upper right. As azimuth is changed (and the phase difference between the two tracks increases), the line will become an elongated oval, and at 90º of phase difference, the waveform will be a circle. As phase continues to increase, the circle will then start collapsing to an elongated oval stretching from upper left, down to lower right. When the two tracks in question are 180º apart, you will see a diagonal line from upper left to lower right.


    When monitoring high frequencies, it is entirely possible to have the head cranked to one side and actually have it appear in phase. This results from the head being 360º out of phase and lining up on the wrong node of the waveform. It is not possible, however, to be on the wrong node for both 1kHz and 10kHz at the same time. For this reason, you must always check azimuth at 1kHz AND 10kHz. If you are on the wrong node for one of them (most likely 10kHz), it will become apparent when the other is checked. Also, lower frequencies will appear as much more stable than higher frequencies. On a well-maintained machine with good heads, even 10kHz will appear solid. However, on a machine in need of a transport alignment, the higher frequencies will be wobbling all over the place, and you must do your best to find a happy medium.

  • Summing Method

    The summing method is a much simpler method of performing azimuth. All tracks from the tape machine need to be summed to the mix buss, either through channel faders or monitor faders. A fader level of -15db is a good place to start for channel faders and the stereo buss. Then, azimuth is adjusted while watching for the peak level on the stereo buss meters. The actual level is not important, just where the peak is. However, in order to have the most accurate reading, you should adjust the stereo buss fader to show the highest level possible. Since all tracks on the head are being summed together (not just 2 and 23), there will be only ONE position where the azimuth will be correct (all tracks summing together and in phase), and it is not possible to align the head on a wrong node of the waveform.

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