Transferring multitrack cassette music to Pro Tools

[yonkiman]

I have some old music from my Tascam 424 that I'd love to copy into Pro Tools and remaster.

The problem is that usually I'd record 4 tracks, bounce them down to 2, record 2 new tracks, bounce those 4 down to 2, etc. So while the first 4 (gen A) tracks are in sync with each other, the 2 tracks new tracks added to the gen B mix-down drift in and out, timing-wise (due to minor speed variations introduced in the bouncing). So while the final 6 or 8 track song sounds fine, the pairs of tracks recorded after the first 4 will not stay in time with the original 4 when you put them all down next to each other.

Is this a common problem? Has anyone written any software/tools to address this? It seems like a problem they might have had creating >4 channel multi-track masters with the Beatle's bouncy mixes, though I'm sure their tape machines had much better speed and wow control than my cassette.

One technique that might work would be if you could detect any of the high frequency bios oscillator tone used when the track was recorded. Then you could frequency lock to that and straighten out a lot of it. Though you'd be relying on the bias oscillator not to have drifted during recording, and it's not exactly a precision circuit. But you could probably detect low frequency shifts, which is where the problem is.

The best way might be to correlate the mixed-down tracks to the original 4, and detect speed variations from that, then apply the inverse to the 2 new tracks on that tape. I'm far from having the DSP skills to implement that, though.

Anyway, was wondering if any of you pros had dealt with this before or if there might be some software that could do it.

Cheers,
Fred

[sw rec]

You'll NEVER get an analog deck to stay in sync, even with itself. That's why we used to use (VERY EXPENSIVE) synchronizers.
Which interface are you using? Inasmuch as you're doing 2 tracks at a time, I would guess an Mbox 2?
Find a pal with an 002/003 and get him to do the transfer...you can do up to 18 tracks at once that way. Or fight with it FOREVER....

[yonkiman]

Originally Posted by sw rec

You'll NEVER get an analog deck to stay in sync, even with itself. That's why we used to use (VERY EXPENSIVE) synchronizers.
Which interface are you using? Inasmuch as you're doing 2 tracks at a time, I would guess an Mbox 2?
Find a pal with an 002/003 and get him to do the transfer...you can do up to 18 tracks at once that way. Or fight with it FOREVER....

That's not literally the problem I have, but it's essentially the same. A better way to describe my problem is that I have 3 cassettes:
#1 with tracks 1, 2, 3, 4
#2 with tracks 5 and 6 (and a stereo mix of 1, 2, 3, 4)
#3 with tracks 7 and 8 (and a stereo mix of 1, 2, 3, 4, 5, 6)

And I'd like to create an 8 track Pro Tools project.

So I know it's a very hard problem, but there's so much amazing DSP out there that I thought maybe someone had solved it. If there really is no solution, maybe I actually will start looking at rolling my own...I just don't want to reinvent a really challenging wheel...

-Fred

[sw rec]

It's still a sync problem. Analog decks just aren't capable of maintaining a stable capstan speed. Those old synchronizers used to compare against the SMPTE stripe up to 9600 times a SECOND. This isn't a DSP issue. Without some sort of sync reference (which should have been in place when the recordings originated but wasn't...nobody ever did sync to a cassette!) you'll never get this to line up. Just be prepared to spend a LOT of time dinking with it. Manually.

[yonkiman]

Originally Posted by sw rec

It's still a sync problem. Analog decks just aren't capable of maintaining a stable capstan speed. Those old synchronizers used to compare against the SMPTE stripe up to 9600 times a SECOND. This isn't a DSP issue. Without some sort of sync reference (which should have been in place when the recordings originated but wasn't...nobody ever did sync to a cassette!) you'll never get this to line up. Just be prepared to spend a LOT of time dinking with it. Manually.

Thanks for your thoughts! The good news is it's not as daunting as you think. Going back to this:

#1 with tracks 1, 2, 3, 4
#2 with tracks 5 and 6 (and a stereo mix of 1, 2, 3, 4)

Basically I'm talking about using the stereo mix of 1, 2, 3, 4 on #2 as the "SMTPE synch stripe" to synchronize with tracks 1, 2, 3, 4 on #1. You couldn't do that in the analog days, but it's theoretically easy to do that with today's DSP techniques and processing power. So you'd essentially have a sync track accuracy equivalent to around 44,000 times a second.

I'm certain it CAN be done, I'm just wondering if anyone has done it yet.

[sw rec]

Just that there's nothing to KEEP it in sync. Trust me, you're going to have to manipulate this manually. Unless you can trick Beat Detective into quantizing it, but I wouldn't hold my breath. The key word here is "THEORETICALLY." Then there's reality....

[yonkiman]

Originally Posted by sw rec

Just that there's nothing to KEEP it in sync. Trust me, you're going to have to manipulate this manually. Unless you can trick Beat Detective into quantizing it, but I wouldn't hold my breath. The key word here is "THEORETICALLY." Then there's reality....

I don't think you quite get it - the cross correlation is like having "beat detective" for virtually every 48/96kHz sample (though every 5ms or so is probably fine enough). The same technique I'm using to get it in sync is the same technique that keeps it in sync throughout the rest of the song.

[sw rec]

Trust me, I get it. I've been doing this for a VERY long time. You can transfer a set of tracks from an analog machine, then transfer the same tracks from the same machine and they won't be in sync. This isn't guessing going on here, this is TONS of experience.
In fact, just the very nature of inconsistent tape machines is what gave us the old "flanger" effect back in my old radio days. You're talking theory, I'm talking practice. But once you start doing it, you'll see what I'm talking about.
"And that's all I have to say about that!"

[cwsand]

I've dealt with this situation a lot with 4 and 8 track cassette machines. The old way I would sync (before computers) is to listen to your music track (mono) of the final tape in the left ear of the headphones, and a combination mono mix of the individual tracks in the right ear. It might take many times of hitting Play to get the songs synched to start, but once they are the music should sound like a centered mono track in the headphones. Then you have to use the pitch control to keep the "sound" in the center. If the tape gets ahead or behind the sound will appear to drift to the left or right. Yeah, technically some of your tracks will be changing pitch but if you can keep the 2 sources synched a without too much drifting it can work fairly well.

A better way that I use for synching audio to video (like taking old 60's and 70's videos and putting remastered CD audio to the video) is to record your tracks from individual tapes to your DAW. Take the tracks you need to synch and cut the silence off the beginning of the track that has audio first and make them all the same length. In your DAW, line the master track up so that the beginning of the wave is in synch with the tracks from the main tape. Then go to the end of the song where it is most likely out of synch. Use an external wave editor (I use Goldwave) to adjust the playback frequency of the track your trying to synch. You have to resample back to whatever your DAW is using, go back into your DAW and see if the end of the song is in synch. If not, go back and adjust the playback rate again until you get them in sync. Once you find the correct playback rate, you can apply that rate to all your other tracks that need to be synched. Of course a long song may still get out of sync somewhere in the middle so you might even have to cut the song in half using the same process. It's a pain but it works. Neither way is perfect by any means, but let's face it - we're talking about cassettes here!!

BTW - I just bought an incredible new book called Recording The Beatles that goes in depth as far as the equipment and recording techniques used at Abbey Road. I believe they did sync machines using the bias but I'm looking forward to reading exactly how they did it!

[rqstudio]

I haven't read all the reply so forgive me if this has been mentioned before.
You could put a beep at the start of the song so at least they will all start together, however it's going to wander so you'll have to manually adjust. Or as one other poster mentioned, get or borrow an 003