Otari MX5050 Tape Bounce Slow Speed Feedback Issue

Discussion in 'Tape' started by bauhaus_bass, Feb 10, 2018.

  1. bauhaus_bass

    bauhaus_bass New Member

    Messages:
    5
    Location:
    Nashville
    Hello all-

    I recently got an Otari MX5050 and am having an issue on it that is really confusing me.

    First off, I am recording at 'slow speed' (7.5 IPS I think). I want to combine 3 drum tracks into one, separate track. I am sending them all via an aux bus on my Allen and Heath mixer onto a non adjacent track on the Otari. Everything sounds fine as the track is armed but as soon as I press record, the track I am recording onto goes crazy, peaking with a high-pitched feedback kind of sound as do a few of the neighboring tracks.

    The problem does not happen when I try at normal (15 IPS) speed. When I listen back from a bounce at this speed, I seem to get some crackle on the track and not as clean a signal as the 3 separate tracks. So I want to be able to bounce at the same speed I am recording at without the machine going ape shit.

    Any ideas about why this is happening? I am at my wits end as I need to free some tracks up soon for overdubbing.

    Thanks
     

     

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  2. Chip Chester

    Chip Chester Super Member

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    1,860
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    So this must be an 8-track (1/2"?) because there isn't one non-adjacent track if you're bouncing three on a 4-track. Are you also monitoring thru the mixer? Sure everything's squared away as far as mixer signal flow? Especially that the monitor channel of the recording tracks are not routed back to those recording tracks?

    (For purposes of discussion, we'll assume the deck is well-aligned, both physically and electronically, and in good general repair including head condition.) Just to be clear, you've got your three drum source tracks in Sel Rep, or whatever the label is for playback off the record head. They you've got your non-adjacent destination track(s) armed, and the fireworks start when you go into record? When you try it at 15IPS, "crackle" on the track may mean there is bleed (or cross-talk, or distortion) either in the head, the wiring, the deck electronics, or the mixer. Try lowering the level on the tracks you're recording to, and see if that makes things better.

    Also try just doing the bounce at 15IPS, even though the master is at 7.5 IPS. It shouldn't matter, except for shifting the frequencies 2x higher during record. They'll come back down on playback. Processing, like reverb, may be an issue due to time constants.

    Is there anything else on the master yet? Because you can bounce without Sel Rep, or Simul Sync, or whatever Otari calls it. Just put source tracks in playback, and bounce 'em. But keep in mind you'll have to bounce all the tracks to new destinations for things to remain in-sync... and additional unnecessary generations on 1/2" 8-track are usually to be avoided.
     
    Last edited: Feb 10, 2018
  3. bauhaus_bass

    bauhaus_bass New Member

    Messages:
    5
    Location:
    Nashville
    Thanks for your response Chip.

    Yes it is a 1/2” 8 track. Newly aligned and newly relapped heads. I am monitoring through the mixer but I’m pretty sure I’m not sending the track I’m recording on back through itself.

    So yes, I’m cruising along monitoring the record-armed track and everything is fine. As soon as I press record, the fireworks start. As I said this doesn’t happen at 15 IPS. I will give the 15 IPS bounce again at a lower level but I’m not blasting at all really. Just trying to get a good strong, low noise signal.

    The other tracks on the 8 track are all used up with other basic tracks.

     
  4. Chip Chester

    Chip Chester Super Member

    Messages:
    1,860
    Location:
    Central Ohio
    Did your alignment go into verifying things like bias filters are working correctly? That could be more of a maintenance thing than alignment, depending on the deck and available adjustments. I haven't used one since about 1985, so don't remember specifics. Can you link me to an online manual from a no-signup site?

    As a test, take just one of the tracks and bounce it using only the XLR connectors on the back panel. Unplug all other I/O XLRs. Eliminate the mixer completely for routing and monitoring. Use the front-panel headphone jack for monitoring. This will tell you if the deck or the mixer/routing is the issue.

    Are you opposed to using DAW techniques to get this done? Such as, adding SMPTE or MIDI to your remaining track, having a DAW chase the deck, then doing submixes and additional tracks digitally? Don't know if you're using analog as the only choice, as an 'effect', or other...

    Also, the use of aux bus gave me pause... Can you try bringing drum tracks into line inputs of mixer, then using a standard bus or even one channel of main stereo out and sending back to deck. Just monitor mixer out, with no tape monitor or aux bus monitoring going on. I suppose it could be console cross-talk if the aux bus is designed to a lesser standard.

    I assume you're running all balanced interconnects, so things like cross-talk within a multi-channel snake (due to poor shielding/bad grounds/lack of common-mode interference rejection) aren't the problem. I've got to say I've never seen any of those before, but it's theoretically possible...

    Of course, depending on what's left to put on those three tracks, you could just do a stereo mixdown of what you have, then lay it on a new hunk of 1/2" stock and have six more tracks to go.
     
    Last edited: Feb 11, 2018
  5. bauhaus_bass

    bauhaus_bass New Member

    Messages:
    5
    Location:
    Nashville
    I am not sure if the guy that aligned it did anything with the bias filters. i am trying to get him back here but that has proved difficult for now.

    I unplugged all the I/o's except for out of one track and into another (non-consecutive) track and monitored from the machine. Same thing. All good and then once I hit record, fireworks again. Also, I did a 30 IPS bounce and once again I could hear some dirt on the new track where there is not any on the original track. Speaking of, the track I bounced was a snare registering around -3 db per hit on average according to the VU's on the Otari (which were adjusted a couple weeks ago too).

    For this project we are opposed to using a DAW for better or worse.

    I will try the bounce using line inputs to stereo out instead of the aux bus and see if that helps. The board is an Allen and Heath ZED 24 so it wouldn't surprise me if the aux busses are of lower quality.

    All I/O's are balanced and switched to 3 pin hot as per the machine's requirements.

    I am thinking about doing a stereo mixdown and then putting it on another piece of tape at this point. Would rather not have to but I think that makes sense.

    Here is a link to some Otari manuals. Mine is a MK III 8 I believe
     
  6. Chip Chester

    Chip Chester Super Member

    Messages:
    1,860
    Location:
    Central Ohio
    A few observances... This machine has 7.5, 15, and 30 ips? Seems I've forgotten more than I remember about it, then. :(
    If the snare is recorded at -3 peak without compression (which is purely a guess), that's still pretty hot. Does this have peak meters? Have you tried a much lower level for the bounce track -- like -10 or less? I know the tape compression may be a desired effect, but it's possible the Sel Sync circuits are not up to the task. Noise gating or other processing could make the lower level survivable.

    BTW, there's no link attached regarding manuals...

    You can still 'hopscotch' tracks on this deck by ignoring Sel Sync and just bouncing from play head. It'll actually be one less generation than submixing, and lets you retain flexibility. Bounce 3 drums to one, mixing. Then individually bounce the other tracks to the newly-vacant 3 drum tracks. When you do them all, they're on the same tape, just a few inches later (because of playback head instead of record head playback) and one generation down. Not a risk-free proposition, of course. And drink coffee instead of beer when you're doing it. Employing DAW or a two-track to archive tracks before committing. Rebuilding would be painful, and probably digital, but not impossible.

    How precious is this recording, both to you and to the performers (which may include you)? I have the comfort of detachment, creatively and geographically, when making these suggestions. I understand that's a luxury you may not have.

    If you go down the playback bounce path, perhaps make a demo recording and try out the techniques to see if you're happy with the results, before changing the original master.
     

     

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  7. bauhaus_bass

    bauhaus_bass New Member

    Messages:
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    Location:
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    Hey Chip sorry for my delayed response as I have not been able to work on this the past few days.

    Before I go any further, this should link you to the manual:

    http://www.sendspace.com/pro/dl/1235q0

    Ok. So I tried again at a much lower level but I am still getting a high pitched squeal as soon as I turn the signal up to an audible level. No dice.

    I tried the hopscotch method that you laid out for me (thank you) and seemed to get the best results thus far. I had a throw away song that I could experiment with and I am pretty happy with it. Not much noise on the new, combined tracks and better fidelity I am assuming than bouncing down to a two track and then onto the 8 track again.

    I forgot to mention that I have another 1/2" 8 track at my disposal. A Tascam 38, which has unbalanced I/O's. I copied everything onto another tape with that just in case. It would probably make sense to back up another one on the DAW while I'm at it but I feel like this would be cheating somehow.

    On the other hand, if I happen to ruin it, I feel confident that we could replay all of it no problem. It would just be difficult to bring the other musicians back. Maybe a good compromise would be to try and leave their tracks alone as much as possible.
     
  8. Chip Chester

    Chip Chester Super Member

    Messages:
    1,860
    Location:
    Central Ohio
    I'll be updating this post over the next few moments.

    Looking over manual now. First thing I see as a possibility:
    The spec for playback is 40 to 25k at 15. 20 to 20k at 7.5 ips. So, good.
    The sel/rep spec is 40 to 15k at 15, and 30 to 10k at 7.5 ips. So, meh. It is what it is.
    However, if an attempt was made during alignment to boost sel/rep playback in the high end, that could be impacting isolation and other parameters. Not saying this is definitively what's going on, but it's a possibility. Most obvious symptom would be increased noise on sel/rep. Haven't looked yet to see if there even is a HF eq in sel/rep, but I'll get there shortly.

    Also, "hopscotch" is a term I totally made up in the moment. Avoid brandishing it about as gospel when discussing this with other engineers; they'll look at you like you're nuts. They'll understand the underlying technique once you lay it out, but it's certainly not a commonly used one. Nor is the phrase.

    ...Another possibility is that the nominal operating level being recorded on the tape has been boosted, to make better use of better tape by maximizing the recorded level, effectively reducing noise. You might be bumping up against the limits of the circuitry and the head. This is not the level in and out of the XLRs, but rather the level out of the record amps to the head itself, and the resulting magnetic 'density' of the recording on the tape.

    ... page 2-7 will cover wiring to and from your unbalanced Tascam if you decide to make a protection master. It should do that fine if you're cabled correctly. Do it with straight connections rather than thru console, unless you want to do submixes and use the protection as the new master (which is a totally valid approach, if the fidelity holds up.)

    ...As I'm reviewing remote switch functions, a thought occurred that there may be maintenance-level problems in the sel/rep switch and/or relay function (which may be solid state rather than mechanical.) The general assumption usually is that the deck is actually doing what it's configured to do, but with increasing age, that's not always a given. If something is not switching audio signals correctly, or is making two paths 'live' when only one should be, that could definitely be an issue. But not an operator issue, rather a repair issue. Deep dive required to figure that one out, if that's the case. Remote box and related cabling could be the culprit as well. Cleaning its contacts would be time well spent.

    ... looping back, looks like there's no sel/rep HF adjustment. I'll substitute bias trap problems as a replacement 'candidate'. Some straw-grasping, though. Figure 7-6 on page 7-16 has a block/board layout diagram showing "Record Timing and Monitor Changing Control Logic". If the deck isn't performing as adjusted, that's the first place to look.

    ... Section 9 is troubleshooting, and they have specific target components for inoperative sel/rep function. In an earlier section is a timing diagram showing state of various devices during certain operating modes and transitions between them. If something isn't selecting or isolating correctly, it shows a baseline of how things should be working.

    Not going to get into schematics tonight -- getting late. But if you discover it's machine and not operator issues, at least you have a good manual for reference.

    But if the so-called 'hopscotch' method gets you thru the session, I wouldn't worry about sel/rep malfunctions right now.

    However, if it continues to flake out when sel/rep recording an outside source (not off tape) like in a standard overdub, then that's a mission-critical function that'll need to be addressed.

    Hang in there.
     
    Last edited: Feb 13, 2018

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