sergxp, yes, that is one way to get that nonlinear analog saturation. Of course, since this is a coloring process, just like any art, there are numerous ways to accomplish this. You may not want that saturated sound across your whole mix.
As you surmised, you can play out a track from your computer, assigning that output to the input of an analog tape machine. You then make sure that this 3 head (it must be a 3 head machine) is in record mode, recording, while it is in playback head monitoring. This output would then be sent back to your computer audio interface input and/or other multitrack recorder and recorded to an available open track. This type of an effect works best on percussive instruments such as drums. Saturating a vocal is not particularly pretty sounding. But guitars and electric basses, Leslie's, are fair game.
I was actually considering purchasing another 24 track analog machine? I used to have an MCI JH 10-16 track which I later got rid of an replaced with a Ampex MM 1200-24 track machine. In 1993, I got out of analog recording altogether. But my friend and competitor has 2 OTARI MTR90 II 24 track machines. I was thinking, since he might let one go for as little as $2500? I might stick it back in the mobile studio and during tracking sessions feed everything through it while in tape monitor playback mode, while its output feeds the 24 track HD 24 inputs and prints to digital 80 ms or 40 ms later depending on speed of the analog machine. Personally, for that purpose, I'd rather have back the Ampex MM 1200 since it was one of the finest recording machines ever made. Some Japanese machines ain't bad and many hits have been produced on those. Bruce bought a pair, which I checked out and tweaked up for him. But he never used them. They now sit at the back of his studio warehouse gathering dust. OK, so maybe $2500 for a good working MTR90II? Either way, if you want that drum saturation, got to have multiple tracks, if you're tracking live like I do. Of course with just a 2 track machine, you can go back, feeding whatever track you want to the analog machine and rerecording it back into your computer. You must do this in real time. That is to say, if you record the track from the computer to the analog tape machine and later rewind the analog machine and attempt to stripe it back into the multitrack on the computer, it won't work. It won't work because tape stretches and there is no time code involve nor time code synchronizer's. So you must actually be recording while playing back while recording at the same time back to your digital machines. Then you would only need to deal with the 40 to 80 ms delay that you could simply slip in the timeline to resynchronize, since no stretching and no time code would be necessary.
Is this method clear to you?
Ms. Remy Ann David
As far as which recorders? Mark Spitz at ATR magnetics features some wonderful, hybrid, restored, modified Ampex ATR 100 series machines and others. He charges a lot for an extremely superior studio machine. Of course, you don't need anything quite like that. A simple used TEAC/TASCAM, properly adjusted will do just fine.
I personally have numerous Ampex and Scully 1/4", 1/2" machines. I have a nice stereo AG 350 in an original portable rack box. It's available and I'm taking offers. Before I let it go, I will put it on the test bench with the test tapes and run it through a full playback and record calibration. I generally use the MRL test tapes (which were originally mastered upon highly modified Ampex 440 transports) and the STL flutter test tapes with the Fidelipac flutter meter. These older machines however, do not work well with what is known to be the last generation of high output low noise magnetic tape. Because of this, earlier/lesser formulations work much better on these older technology machines. The problem in the past had been one of erasure. The older machines just could not erase enough of the previous track. You could hear it in the background. No amount of the erase or bias energy seemed to solve that problem as the erase head core would saturate. Later, a German manufacturer seemed to come up with an erase head, that would completely erase the tape. They were made by a company called Wolke. Their erase heads did not include a guard band, at the center of the two channels but rather 2 staggered 1/8" wide erase head tracks, in the same body. Scully nor Ampex ever adopted those heads but MCI and Studer did.
If you get your hands on an older used TASCAM 7300/3300, etc. or better still an Otari MX50-50, I'm sure you can find them for only a couple of hundred dollars on eBay. 1/4" tape is still available from companies like Sony and Maxell. Those tapes should function properly on these older machines.
Let me know if you are interested in either an Ampex AG 350 stereo machine with germanium transistors or a Scully 280 A stereo machine with germanium transistors or a Scully280B mono with silicon transistors. These are collectors items and all are in beautiful condition. I also have numerous spare parts and heads along with major assemblies, motors, etc., available.
Old Scully quality control manager and final test technician
Ms. Remy Ann David