No O'scope Azimuth Adjustment Procedure





If you don't have an oscilloscope, you can still adjust azimuth, and be 
as accurate as with the o'scope!!  

Remember that ALL consoles are "Voltage amplifiers", and that 
all of the VU meters on a professional recording console 
(as well as most Semi-pro boards) read the output voltage (and NOT THE POWER).

============================================================
  Two equal and in-phase VOLTAGES will add by 6db 
when selected to the same output buss VU meter.   
============================================================

Thus you first patch the tape recorder's 'outside' tracks
(track 1 and 16 or 24)  to 2 different input channels of 
your board, making sure that the board's eq is out, and that there are 
no Echo Sends or Aux Sends on. 

Then select just ONE channel (say Track #1)
and send it to any one buss (say "Buss 1" out of the console). 
Set this one track's channel's fader level on the console so that 
your 'Buss 1' output VU meter reads -6 VU.  

Then turn OFF that channel. 

Next turn on your other channel, (it would be Track 16 for a 16 track, 
track 24 for a 24 track and so on...) send it to the SAME buss as the 
other channel you just setup, again set that track's console fader level 
so the Buss 1 output meter AGAIN reads -6 VU. 

Now both channels are set to read individaally at -6 VU on the SAME buss Meter
where either one is turned on alone and the tape is reproducing tones.

 Then turn BOTH channels on.  Since two in-phase VOLTAGE signals should add 
together by 6 db, you now should be reading 0VU on the meter.  

If the meter is very near 0 VU and is stable (not moving around much), you're ok.
 
ALWAYS check another frequency!!!  Use 1khz and 10khz and 16khz if possible.

If the meter reads less than 0 VU, adjust azimuth 
until the meter reads as close to 0VU as possible, with as little meter 
movement as possible.  

Make sure re-set your -6 vu levels on each channel 
after making any azimuth adjustments !!! You MUST check azimuth with more 
than just one tone.... use 10khz and 15khz if you can as well as 1khz.

Check that each frequency is at the correct individual track -6db VU level,
and that they add together about 6 db, reading about '0VU' when summed.  

Once you have correctly set azimuth, all tones should read close to 0 VU and be stable.

Of course this assumes that your tape machine is properly aligned, and that
all tones reproduce at '0 VU".

Note that often tones will not quite get to the full 6 db increase -
often you'll get only about a 5.5db increase which will show up as a
-1/2 db on your VU meter.  this is OK if all the tones are stable and 
right around this level.

Also you MUST use a GOOD ANALOG VU METER!!!  Most LED vu meters don't 
have the resolution to show small increments, so you cannot use 
LED meters!!!

This then will allow you to set azimuth quickly and accurately without 
having to use an oscilloscope!!!  


In case you forget how much two in phase VOLTAGE signals add,
you can always first try it with an oscillator (which every good board has),
connect the oscillator to two input channels of the board. Use this perfectly
in-phase signal to check what you're doing.... Try it.... it really works!!

Note: You probably remember that 2 in-phase signals rise by 3 dbm... but that's POWER (voltage times current) and not just VOLTAGE. Just using VOLTAGE ALONE means the signal as indicated on a professional VU meter will rise by 6 db. Note I didn't say 'dbm'! Dbm is actually a POWER measurement, while just using db (and not the added 'm' designation) means the measurement is just a logarithmic relationship of any 2 signals that are of the same stuff... in this case Voltages. Hopefully you'll want to know more... and there's a whole page on db's here in this Web Site!


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