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Mix Bus: Using Cassette Decks as Analog Processors for Your DAW

4/3/2008

Well, there’s a way to fix this that doesn’t require buying an old Studer deck. The answer is cassette decks. Companies such as TASCAM made decent-quality 2-track recorders and multitrack units with three heads that are way cheap on the current used market.

For a quick tape routing and procedures discussion, read the 12/07 issue of EQ [“Kissing the Sky”], and calm down. You need not risk creative-flow inertia when doing all the required patching and procedures. With a three-head tape recorder, you can record a DAW track to the record head, pull the signal from the playback head after it’s been processed by the tape, then send the processed signal back to your DAW. This is pretty close to a realtime process, except for the delay caused by recording at one head and playing back via a head that’s positioned later in the tape path (don’t worry, we’ll get to fixing that shortly). Wiring the output directly to a dedicated stereo I/O on your digital interface can give a “processed-by-tape” effect that’s almost as convenient as a plug-in.

SAY WHAT?

Because of the time it takes for the tape to travel from the record head to the playback head, we’ll end up with an out-of-sync track when we bring it back to the DAW. Recording drum hits or click references would allow us to slide-adjust the tracks to each other—but setting that up takes time, and you want it now. So, here’s another sync approach that you need to set up just once, and then you’ll know how much to compensate for the delay in future projects. We just need to find the precise delay your tape recorder generates. To do this:

  1. On an empty DAW track, record or copy a three- or four-second sine-wave test tone at roughly –12dB. I used a 1kHz tone from a cable checker (Figure 1), but most digital audio editors can generate sine waves for testing. Label this new track “Test.”
  2. Zoom way in to the sample level. Split the track right on the zero crossing that begins the upward journey of the first complete waveform. Delete everything to the left of the split. What should remain is a signal that begins with a zero crossing directly at the left edge (beginning) of the clip.
  3. Send your “Test” track through separate (not main) stereo outputs on your DAW interface directly to the stereo inputs of your tape recorder. Return your tape outputs to stereo inputs on your DAW. 
  4. Set the tape recorder to monitor from the playback head, load a blank cassette, put the recorder into record mode, and start running tape. Leave it running.
  5. Play the “Test” track through the tape recorder back to the DAW, and record this on a new DAW track. Label this new track “Delay.” Then, visually compare the offset between the start of the “Test” and “Delay” signals to count the milliseconds of delay (Figure 2).

WAIT A MILLISECOND . . .

I get frustrated when I try to count milliseconds. So I use Sonar, which provides an easy time-adjuster called Nudge (look under the Process menu for “Nudge”). But I still have to know the count before using the tool. So if your DAW won’t easily let you grab a count, create a very small reusable “measuring stick” instead by making a new track clip trimmed to equal the space between the onset of the “Test” and “Delay” tracks.

  1. Duplicate the “Test” track with its tone, and insert it between the original “Test” track and the “Delay” track, making sure the duplicate stays exactly in sync with the original “Test” track.
  2. Re-label the duplicate track “Adjuster.”
  3. Zoom in and place your vertical Now Time cursor at the onset of the “Delay” track—right on the zero-crossing sample that begins the waveform.
  4. Split the “Adjuster” track at the cursor. Delete everything on the “Adjuster” track to the right of the split. You now have a tiny template clip you can use to visually show the delay between the tape heads (Figure 3).

Still want to know how many milliseconds of offset exists between the original track and the one coming back from the cassette tape? Don’t do the math—just slide your handy template all the way to the left, to zero on the time line (the start of the project). The right edge of the clip now lines up with the correct number on the time ruler (set to milliseconds, of course). Zoom in to get sample accurate. Afterwards, you can discard the “Test” and “Delay” tracks, and save your “Adjuster” template track for future use. Consider renaming it to identify the machine it calibrates, as different machines have slightly different delays. The delay will be the same every time you use that machine.
Before you save, note that Sonar has a right-click command called “Trim” that permanently saves the clip to its new size. Other DAWS will have something similar. Until you trim, the right and left edges of the clip can be accidentally slip-edited out of place, and your careful calibration will be lost. After you apply trim—even if you slip-edit the edges—the waveform graphic will still show the calibrated edit points (Figure 4).

TIME FOR CORRECTION

With delayed tracks, it’s simple. All you have to do is follow these directions and you will be good to go.

  1. Insert a copy of the “Adjuster” measuring clip track just above or below the track to be adjusted.
  2. Slide the “Adjuster” clip to line up the tail of its waveform graphic with the head (signal onset) of the delayed track. You can zoom in and use the vertical cursor to help get it sample accurate.
  3. Now, slide the delayed track to line up with the head of the measuring clip (Figure 5). 

There, that didn’t hurt, did it? Kind of makes you want to reach for the tape option more often. You can even make an “adjuster” track for any outboard device that introduces a fixed delay. Try it. You’ll be glad you did.

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