Tape Recorder Tests and Checks...

Here are some simple tests you may want to make if your recorder is either
new or hasn't been in use often. 

First CLEAN the machine very very well.  De-mag it.  Put "scrap" tape on the 
machine and put the machine through the basic transport functions.  Here
you're just making sure that the machine operates correctly.



The Second thing to do is to record a 1 kHz tone onto only ONE TRACK,
play this tone back AFTER recording it onto tape, and listen for any 
"waver" of the tone.  What you're listening for is the pitch of the tone
changing.  If you hear the pitch changing, this indicates the machine has
a lot of "Wow and Flutter" and is not in good condition.

Do NOT compare this tone to the oscillator, just listen to one track of the 
machine, in Repro, and pan the channel's pan-pot to just one side, so you're
listening only to one speaker.  A well maintained  machine should have No
audible Wow and Flutter.



Next you'll want to do a basic alignment, paying particular attention to
the High Frequency Repro and Sync response.  There should be minimal 
fluctuation at 10khz.  MCI's usually "waver" about 1/2 dB or less at 10khz.
Studers, Otari's and Ampexes usually have less waver.  Of course worn heads
or a mis-aligned transport will cause more high-frequency waver.


 The next thing to do is to test erase by recording a 1 kHz signal at
operating level then rewinding the tape to the pre-recorded 1 kHz section. 
Then remove the input signal and begin recording again.  Monitor REPRO. 
Listen only to ONE TRACK at at time.  Increase your monitor level (board 
or power amp level) until you hear tape-hiss.  Only a extremely small 
amount of the tone should come through, if any at all.  If a lot of tone 
comes through, the machine is not erasing properly, and it should be 
brought to the attention of a technician who can properly do an erasure
alignment.




The next test is to go to a blank section of the tape, and record, 
without an input signal, monitoring REPRO.   All you should hear is a 
nice constant hiss, not pops or "tape gravel", and no hum.  This 
indicates that the machine is in good operating condition and does not 
have any noise problems.




A third test is to record a 1 kHz section at the head of a tape, then turn 
the tape over (the recorded tone is now at the tail) and replay the 
recorded tone, and compare it to the oscillator that fed the recorder.  
Listen for a change in frequency between the oscillator and the tape.  
If drastic, the speed is changing between the head and tail of the tape.
NOTE THAT YOU WILL ALWAYS HEAR SOME "BEATING" BETWEEN THE OSCILLATOR
AND THE TAPE...  but there should be no great change in frequency.




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.   Thus you first 
patch the tape recorder to 2 different input channels of your board, 
making sure that the board's eq is out, and that there is no Echo Send 
or Aux Sends on. Then select just one channel (Track #1)and send it to
any one buss. Set that one channel's fader level so that your buss 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, and again set that
track's channel faderlevel so the buss output meter again reads -6 VU. 

 Then turn BOTH channels on.  Since two in-phase signals should add 
together by 6 dB, you now should be reading 0VU on the meter.  If the meter
is near 0 VU and is stable (not moving around much), you're OK. 
Check another frequency 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.  Once you have 
correctly set azimuth, all tones should read close to 0 VU and be stable.

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 signals add, you can always first try it with an oscillator (which 
every good board has), connected to two input channels of the board.   
Try it.... it really works!!