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How to use AudioTester program
for the azimuth adjustment in a tape recorder



This page explains how AudioTester program can be used to adjust the head azimuth on a tape recorder using Wavegen and Osci components of AudioTester.

Part 1 - Recording of the test tape



The sound card set for 96 kHz sampling rate and 16 bit in the program settings for both Wavegen and Osci.
The line output of the sound card is connected to the input of the "reference" recorder to record the test tape with 10 kHz -20 dB signal.
The line input of the sound card is connected to the output of the "reference" recorder during the test tape recording.
Later the line input of the sound card is connected to the output of another deck which is in need of adjustment.
To align the head on that deck we play the freshly made "reference" tape on it and adjust the azimuth by rotating the azimuth adjustment screw on the playback head.
Location of the screw is usually shown in the service manual.

Obviously, if you have a factory made azimuth alignment tape you may skip the first part - how to make the test tape.
In any case by making the test tape on a "reference" recorder you only can set the azimuth as good (or as bad) as on your "reference" recorder.
It makes sense if you have a large number of tapes recorded on that machine and would like to align the second deck the same way or if you have your "reference" serviced and aligned recently by a qualified engineer with a proper azimuth alignment reference tape.

Picture 1 Level_set_source shows the Wavegen set to produce 10 kHz sinewave at -1dB digital scale. Use this signal to adjust the record level knob on the "reference" deck for 0dB on the level meters.
After that reduce the level in the Wavegen from -1 dB full scale to -21dB - that will give you the correct level for -20 dB recording (picture 2, Level_set_source_minus_20dB). Note the 10 times change in the vertical scale in Osci.
On the next picture (3, Source_minus_20dB) I've increased the horisontal rate to 20us/div for better visibility of the phase difference between channels
Now, using a good quality tape, record 5-10 minutes of this signal. To test the recording you should play it back on your "reference" deck first. That is what I have done to produce the following pictures.
I've used Nakamichi Cassette Deck 1 to record and play back the tape, as it has a playback azimuth adjustment knob on the front panel and I could easily misalign the playback azimuth to show the effect of it on the screen of Osci.

Part 2 - Adjusting the Azimuth!



The second and most important part. You may need to use only this section if you have a good quality pre-recorded azimuth alignment tape.

The sound card line input is connected to the output of the deck which is in need of adjustment.
The test tape (factory made or made as described in Part1) is played back on the machine we plan to adjust.

Important:

1) The deck you are trying to align should be OK from a mechanical point of view, the heads should be demagnetized, the tape speed and playback level really need to be adjusted prior to the azimuth alignment. Please refer to the service manual for your recorder for information on how to do that.

2) If the azimuth is reasonably correct (the phase shift is not more than +/-45 degrees) you better not to touch the azimuth screw as this kind of deviation can easily be due to a particular tape or cassette shell used.

Picture 4 Tape_az_OK shows a perfect azimuth alignment, with the output nice and high on both channels and near 0 phase shift between left and right channels. That is what we aim to achieve.

Following pictures show how does it look like if the azimuth is misaligned.

Picture 5 Tape_az_1left shows what happen if I turn the azimuth knob on my Nak one full division left.
As you may see the level of two signals is still high, however the phase is out by half a period - 180 degrees.

Picture 6 Tape_az_2left is for the azimuth knob full 2 divisions left.
The signals back in phase, however the level is dropped and uneven between channels. The azimuth is far off the correct position.
This picture shows that you need to pay attention to both the level and the phase shift - the first gives you a rough position for the azimuth and the second allows for a fine tuning.

Please bear in mind that not all decks are able to hold the azimuth very steady, as my Nakamichi Cassette Deck 1.
On lesser decks two signals on the screen will move in relation to each other and your task in this case is to align the azimuth in such a way that the average position of two curves would be close to the ideal as shown on Picture 4 Tape_az_OK.

Pictures 7 and 8 show that the effect is the same if the PB azimuth knob is rotated right by 1 and 2 divisions respectively.

Last 3 pictures show how to use Osci X-Y mode to align the azimuth. It is more sensitive and more precise - you can try it if your deck is good and the azimuth is stable.

Level_set_source
Level_set_source 		Level_set_source_minus_20dB
Level_set_source_minus_20dB 		Source_minus_20dB
Source_minus_20dB 		Tape_az_OK
Tape_az_OK 		Tape_az_1left
Tape_az_1left 		Tape_az_2left
Tape_az_2left
Tape_az_1right
Tape_az_1right 		Tape_az_2right
Tape_az_2right 		Tape_az_OK_XY
Tape_az_OK_XY 		Tape_az_0.5_left_XY
Tape_az_0.5_left_XY 		Tape_az_1_left_XY
Tape_az_1_left_XY

JAlbum 7.1