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In working with iZotope's RX2, I see it has a feature it calls "Azimuth adjustment". Below is a screencap from the Helpfiles:
What on earth does this mean?
Seems like it tells you right up top.
Using actual tape required adjusting the rotation of the heads (azimuth) as part of the setup. If the azimuth was off, one channel would record just a fraction of a second before the other so the phase / gain / EQ would be slightly off from what the input signal actually was. A tape machine that wasn't set up and calibrated correctly made tapes that only sounded "right" on that machine.
Sounds like this plug lets you fix tracks that were recorded or converted to digital on a tape machine that was out of alignment. Or, I suppose you could use that feature to simulate that sound though I can't imagine why.
Just a guess though.
P.S. I should add that azimuth is the rotation seen as circular if you were to look straight through the tape at the head from in front of the head. Of the three possible rotations azimuth is the one commonly done each time you align the tape machine. Generally you used a scope set to show lissajous figures which indicated the phase difference between the L and R channel. Apologies if you already know this and I misunderstood your question.
"Azimuth" in this context refers to tape recorders. It's a measure of the perpendicularity of the head gap relative to the horizontal tape motion. It's the real alignment part of "tape recorder alignment" since it's purely a mechanical adjustment - you turn a screw to tilt the head.
Ideally, and this is the idea behind "alignment," a tape will be recorded with the record head azimuth adjusted correctly. If it's played on a recorder where the playback head azimuth is incorrect, there will be a loss of high frequencies - more loss the further the misalignment. Also, if it's a stereo recording, one channel will be delayed relative to the other (think about the trigonometry) resulting in the channels being out of phase.
Azimuth is adjusted by setting the head for the most high frequencies, and, if it's a stereo head, fine tuning the adjustment to put the channels in phase. Multitrack heads have "gap scatter" which means that the gaps (where the tape magnetization is concentrated) are not in a perfect straight line. When you have more than two, you can't get them all perfect. Score one for the DAW that works correctly.
I suspect that what this plug-in is doing is adjusting the delay between channels to bring the channels back into phase. It may also make assumptions as to how much high frequency loss occurs based on the amount of delay required to get the channels in phase and boost the highs as it adjusts the delays. Its intended use is probably to "correct" a tape that's been played on a deck that didn't get aligned to match the recording.
I suppose that there are also some "creative" uses for making a good recording sound like it was played back on a misaligned recorder.
"Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
Drop by http://mikeriversaudio.wordpress.com now and then
Azimuth isn't just the head tilt, its also the height of the head in relation to the recorded track playback. A head can be vertical to the tape and only be playing back half the tracks waveform.
This is where a scope comes in handy. If the head is too high or low, it can cut off the positive or negative side of the sine wave. A scope allows you to center the waveform so both sides are equal. Then you superimpose a pair of heads waveforms and adjust the tilt so the two are aligned.
The bottom of the tape head will have the adjustments. When you tilt it left or right the top channel will move much more than the bottom head will. The scope will allow you a visual for the best center.
Often times heads have a tilt that's front and back as well. This one is quite critical because it can not only sound bad, but it can also damage the tape. If for example, the head is tilted forward, the tape will have more friction at the top and it will tend to drift downward. This damages the bottom side of the tape as it rubs against guides but the higher friction on the top of the head will heat and stretch it.
Tilt left/right/front/back and height all fall under the azimuth heading. You have these adjustments for both the record, playback, and erase heads as well. A playback head can be jacked up by someone who doesn't know the record head is off for example, or worse yet, they think a frequency imbalance or loss of highs is an azimuth problem where its actually a worn head.
A worn head causes more friction and more tape damage. There again if a tape head is worn unevenly, it can be caused by improper tilt or worn drive components that can also cause tracking issues. A worn Caspian bushing can cause the tape to ride high and cause azimuth issues (a more likely cause than the head moving) or an idler roller can get rounded and the tape drifts up and down as it moves causing azimuth wow.
Then there's the takeup motor/drive action of keeping steady tape tension on the heads. Too much tension and it stresses the tape, increases head wear. If you compound it with worn idler pulley, tape can slip past the Caspian and you have flutter. Too little pull and you can have poor tape contact on the heads. Again this can be misdiagnosed for a head alignment issue when its actually a drive problem.
Then you have gravity that's a big factor on the adjustments. Running a Reel to Reel in the vertical position gets rid of gravity pulling down on the tape and causing the tape to sag on the heads, but the Caspian shafts have more wear. Caspians often have counterweights on the back to reduce mechanical speed fluctuations of the motors driving them. This weight can chew up any bearings or bushings and accelerate the problems with the tape transport components remaining parallel to the heads. Rewinding tape at high speed causes these components to heat up and wear more the same as an electric drill does drilling through metal.
For all there's reasons I don't miss maintaining analog gear. I used to be really good at scopeing heads up to specs. Since its difficult or impossible to get new parts any more you had to do what you could adjusting the gear with worn parts instead of just changing those parts to get proper tracking back.
The best method is to either use a factory test tape, and first align the playback heads for maximum sound quality, then adjust the record heads to play back to the aligned playback heads. If the erase heads are separate, you monitors the noise level as the tape erase and adjust for the lowest noise floor erasing a pre recorded tape.
On a pro multitrack deck, you could adjust the playback heads to match the recording heads "if" you trust them being in alignment. Problem is, if they are out, the recorded tracks may play back fine on that particular deck, but the tracks may not play back properly on another deck.
Again, this is fun stuff if you enjoyed doing the maintenance, but it can be a nightmare trying to get any kind of reliable tracking consistence if you have compromised transport components. Add in worn tape and its just that much worse. Digital is a blessing from God. I do not miss having to deal with mechanical deficiencies. They went as far as they could with that technology and it always came back the the physical components wearing out or just not being good enough to begin with.