Tape Project Forum
General Category => General Discussion => Topic started by: stellavox on April 15, 2009, 09:58:52 AM
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I've had this discussion with a few of you enough times to warrant posting the idea here.
Project subsctibers apparently receive a 15ips alignment tape with IEC equalization. For NAB EQ you are out of luck. When you go to MRL you find that their "normal" tapes are one speed / one EQ only, and getting multiple tapes runs up a big bill real quick.
A few years back, I needed an alignment tape for my Sound Technologies 1500A and contacted MRL about making me up one "all purpose" tape with different speeds and EQ's. They did and a 3 speed, 2 EQ tape cost me less than two single tapes.
Here's what I propose. If there is sufficient interest, I'll contact MRL and see what they will charge for the following tape: 15ips - 30 seconds reference tone (250mw?), 60 seconds 10khz (or whatever HF tone) for azimuth adjustment; then say 15 seconds (each) of a series of 5? or 6? tones with IEC EQ, followed by the same number/frequency of tones at NAB equalization. THEN, the same thing with NAB EQ ONLY for 7 1/2 ips. Now you should have everything you need on one tape for most all playback needs - UNLESS you also want 3 3/4 ips NAB playback EQ.
I'm guessing that we could get a pretty decent price if we could guarantee MRL a quantity of say 6 tapes.
Waddyathink????
Charles
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I think for NAB 15 IPS and 7.5 IPS is considered the same so if you have the IEC tape from the tape project then all you would need is a NAB 15 IPS calibration tape.
I'm up for it since I don't have the tape project calibration tape and would love to have an all in one.
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I'd be interested, depending on the price.
MRL has some 2-speed cal tapes, but they are either NAB OR IEC and they are only 2 tones each, 1kHz and 10kHz, IIRC.
That of course would be of no use to correctly set repro EQ.
Thanks for offering to look into this!
Andrew
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Brad,
7 1/2 and 15ips NAB playback EQ are the same, but what happens when you play a tape recorded at 15ips at 7 1/2ips?
Charles
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You hear the music much slowwwwweeerrrrr. :)
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Charles,
I would definitely be interested in one of these "all in one" alignment tapes, so count me in!
Dan
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Charles,
If you can make this alignment tape happen from MRL at a reasonable price, Put me down for one.
Richard
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I would be interested also.
Brian
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Hey Charles,
Looks like this has gained at least 6 interest already :).
Here is a post Doc made in the past of what is on his alignment tapes.
http://www.tapeproject.com/smf/index.php?topic=685.msg3870#msg3870
I would say this would be the minimum requirements for an IEC and NAB alignment tape at 15 IPS.
One question I have is what would be needed on the tape to check the accuracy of a IEC and NAB eq?
Doc can you or anyone else chime in on anything else that would be needed on a tape like this?
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Wow - youse guys are quick!!
Let's see - from the posts so far I see the following potential test tape:
15ips: 30 sec of 1Khz reference; 60sec 10Khz and 60 sec of 15khz for azimuth adjustment
15 sec each 30, 60, 90, 1K, 10K, 15K all at NAB EQ
same as above at IEC EQ
finally 15 sec of 1K assymetrical
7.5 ips same as above except NO IEC tones
If my addition is right we end up with a tape that is a minimum of around 10 min long which could be expensive. Let's see what MRL says - I will also ask them for suggestions to bring the cost down.
To answer ecir40's question about test equipment, I think you could get by with a "decent" Digital Volt Meter (DVM) HOWEVER you need to look at the accuracy spec for it's high frequency AC response. The simple circuits in many "cheap" meters don't allow for good accuracy above 1Khz or so. For example, my (cheap) old Radio Shack DVM has +-1% accuracy on DC, +-1.8% accuracy on AC up to 1Khz degrading to +-6% above 1Khz! As we are dealing with sine waves here which should have low distortion, the True RMS capability of more expensive meters MAY not be necessary - unless it's the only way to also get accurate high frequency response. To use the meter, you could hook it up to the output RCA jacks of the playback amp.
Doc's posting on how to set azimuth is a good one and of course having/knowing how to use a 2 channel oscilloscope is a real plus as you can "see" what's going on with both channels simultaneously.
Charles
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We would be interested in a 1/4" version of the multi-format alignment tape as described in the previous posting by Charles. I am new to this forum and do not know if there is an existing assumption about tape width in this case, but 1/4" and possibly also 1/2" would be useful to us.
I will be interested to see how MRL responds to the inquiry.
John
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Just so you know, it's possible in some cases to use one tape to align to a different standard. There's some pretty good information on the MRL site about it. For instance, you can use your IEC tape to align for NAB, just set the 10K tone to +2.5. Conversely you can align to IEC with your NAB tape, just set the 10K tone to minus 2.5 and it'll be close enough for more purposes.
For another instance, you can play a 15 IPS IEC tape at 30 IPS and align to the AES curve, or play it at 7-1/2 IPS and align to IEC.
More Stupid Test Tape Tricks can be found in the extremely useful MRL publication "Choosing and Using..."
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Something along the lines of an HP 410C or 400GL or 3400 AC rms voltmeter can be had pretty cheap these days and they typically have a bandwidth that goes from 20Hz to several MHz.
Here at the Chateau we use a Tek TDS 420 oscilloscope. It's a scope that allows you to assign a number of measurements to each of four traces. We just set it up for dual trace, take a measurement of rms AC volts from the repro, and rough out the rms to dB conversion in our head. Since we are adjusting the heads to hit the same voltage at every frequency rather than trying to log painstaking response curves this works quite well. And of course we can switch to X-Y display on the fly to adjust azimuth. I've watched Mike Spitz align an ATR and he does it pretty much the same way.
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Sent a "preliminary" Email to MRLyesterday outlining what we might be after - will forward their comments. Did knote that one of their typical 5 minute tapes cost ~$135 and a 10 minute tape $200 - so there's the probable range of costs.
Paul is of course right that with the necessary info you can "correct" the various spot frequency readings from one EQ to another, and that his referenced MRL publication does have a lot of the necessary charts: HOWEVER this requires stretching one's (limited?) knowledge perhaps to the breaking point. May be easier to spend some (reasonable amount of???) money to avoid this meltdown.
Want to add that to my first point on monitoring the tones should you have a test tape - in addition to hooking up a meter to quabtitively monitor the output you need to be able to hear what's there simultaneously so you know where you are on the tape - so I'd suggest hooking up the meter in PARALLEL with the preamp output. Could do this simply with a RCA "T" adaptor and a cable with RCA connector on one end and the other end terminated with whatever connector you need to plug into your meter. Most meters have sufficiently high input impedance that you won't load down the source at all.
Charles
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Want to add that to my first point on monitoring the tones should you have a test tape - in addition to hooking up a meter to quabtitively monitor the output you need to be able to hear what's there simultaneously so you know where you are on the tape - so I'd suggest hooking up the meter in PARALLEL with the preamp output.
Or you can just plug headphones into the headphone jack, and the meter to the preamp outputs. That's what I normally do when using test tapes.
BTW, I fully agree that you need some way to hear the test tape when you're using it.
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Charles,
Did you ever get a reply from MRL?
Brad
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Yes Brad,
Sorry for any delay but I've been a bit busy.
Jay responded that he already makes available a "single format" type tape available with the following tones:
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Magnetic Reference Laboratory Pub 352x
P352, Short Program, All at 0 dB; no voice announcements other than intro. For 7.5 in/s, and fluxivity > 250 nWb/m, must be at -5 (or -10) dB.
White noise 25 s(seconds)
1 kHz 25 s
10 kHz 35 s
16 kHz 20 s
50 Hz 10 s
100 Hz 15 s
SlowSweep, 20 Hz...20 kHz 25 s
Total running time, 2' 47" (2.8 minutes)
For instructions on using the White Noise, please see
http://home.comcast.net/~mrltapes/pub702.pdf
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Charles's note: hope you're following this so far. The above between the dotted lines is copied from Jay's attachment - wanted to put it in color or italics but can't get any of those buttons to work. The white noise "tone(s)" are new to me and are apparently another means of azimuth alignment - refer to Jay's publication. BTW if you haven't been there, Jay's site contains a WEALTH of invaluable tape info!
IN ANY CASE - this program in a "single width, single speed, single EQ" format is available from a separate source for ~$100. Jay is willing to put three of these programs together in 1/4" format: first - 15IPS NAB, next 15IPS IEC, finally 7.5IPS NAB. The cost for this tape would be $155 (didn't ask if this includes shipping??). He said that adding an assymetrical tone would add ~$10. Didn't specifically cover this, but I'd suggest that the reference fluxivity be 250 nWb/m
SO we're looking at around $165 as the cost for ONE tape. If we can guarantee him 6 or more tapes he will give us a discount of 25% each bringing the cost down to around $125 (which I'd opine is an absolute bargain).
Here's what I'm willing to do - primarily to save Jay a hassle and make it a "single" order . Anyone interested will send ME the final amount (don't know shipping cost yet). If/when I get "orders" for 6 (or more) I'll forward the info/total payment to Jay for "processing". Am hoping that he can send the individual tapes to their owners himself rather than the whole batch back to me for "resending". If I don't get 6 (or more) checks, I'll tear them all up!
SO, at this point I guess I'd like to see how this concept "floats" with youse guys. Do you understand the "program" and are you comfortable with it? Then do WHO'SE IN - do we have 6 or more. Please note that I may NOT be participating as I already have the same kind of program tape made up to synch with my ST1500.
Charles
The
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Hey Charles, I'm in for one of the 7 1/2 ips NAB tapes.
I'm close enough that I could almost walk there,.. but I could drive over, pick up the tapes and UPS them to the guys.
It would be great if they could already be packed for shipping but if that's any problem, I could do that too (especially if we could get an additional discount for that). There's a JDM packing and shipping location right around the corner that I use all the time (and obviously, mine doesn't need to be packed).
PM or email me if there's anything else that might help (actually, I'd love to go over and make the tapes but I don't think Jay would be too keen on that!).
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What about adding a series of pops to check polarity at the speakers like on the Tape Project alignment tape mentioned in the last paragraph of Doc's post here.
http://www.tapeproject.com/smf/index.php/topic,685.msg3870.html#msg3870
I haven't used a alignment tape before so I do have a few questions that could use some clearing up.
IEC 15ips part would be needed for 2 track and the NAB 7.5ips for 4 track. Does this need to be specified? What abut NAB 15ips?
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I'll just throw in here that it would be a really nice feature for a lot of folks here who play 1/4 track prerecorded tapes to have an alignment tape for 7.5 ips NAB 1/4 track tapes that is recorded in 1/4 track format. Using a full track or two track tape makes accurate alignment of the 1/4 tracks a bit more difficult, particularly if you don't have a scope. But that means a different head setup on the tape machine making the alignment tapes and therefore probably out of the realm of the tape you guys are discussing.
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Hey Doc, being green to this that was one thing that was puzzling me about an all in one tape.
Just so I get this clear two alignment tapes like in Charles post above would be needed. One for NAB 7.5ips 1/4 track (prerecorded tapes) and the other for IEC 15ips 2 track (tape project tapes). Don't see a need for NAB 15ips unless you have plans to record in this format.
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Charles,
I'm definitely still interested in one of these tapes. Keep me on the list.
Thanks!
Dan
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Since we've only had one person (Dan) express interest in getting the "special" tape, I'm going to forget it.
Regarding some other responses: Ironbut - the tape I was proposing was three sections - 15 ips NAB and IEC and 7 1/2 ips NAB. If you want a single speed tape you can go here:http://www.audiovillage.org/gear.html. ECIR40 if you read the "special" tape description youll see that we were adding an asymmetrical tone for polarity instead of "pops" - don't know if MRL does pops. Doc - since you mentioned it; who makes a four track alignment tape?
Charles
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Hi Charlie,
I don't know if anyone makes a quarter track alignment tape. I think Paul mentioned that all of the MRL tapes are full track mono. That's perfect for making sure that the phase is true for azimuth adjustment, but having quarter track tones at 1K, 10K, 15K would, I would think, make fine tuning a 1/4 track head a bit more precise. Maybe we will make one of our own one day, but it means knocking one of the slaves out of service for a day since we would have to swap head stacks. So it's not really a priority right now.
I wonder if Ampex ever made them?
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Doc,
Am I right that the only reason you might want a 4 track over a full track is to get the head "height" adjustment right? And the problem here is that if your "goal" mainly listening to quarter-track prerecords, you are really at the "mercy" of the calibration of the high speed reproducers used to make them. To date, tweaking the height adjustment (only) by sight seems to work just fine.
Charles
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The reason I haven't responded is that Angel, my tech made me allignment tapes for both my Ampex ATR-700 (2 track only at 15ips), and my Akai GX-747dbx (4 track at 7.5ips both directions, since it is a reversing machine). He had alligned and calbrated both machines, setting bias, etc. Don't know his source for the four track. Larry
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We do find that fine tuning by ear with a set of cans after we do the visual alignment can help - and that the height can be off a bit on the next 1/4 track tape you put on because of the variation in cal of the duping lines, as you mention. That's what tends to lead me to the idea of putting a 1K ref tone and then a couple of HF tones on a tape on an accurately positioned 1/4 track, to create some sort of point to return to if you find that you have to make tape by tape tweaks to the alignment. How easy it would be to make it "accurately positioned"? I dunno, 1/4 track is what it is, and maybe you are right that it's not worth it and a visual is good enough. One interesting issue we found early on is that clear leader can run at a different position on the head than oxide coated tape. So when we would try to do the visual with the moving clear leader we kept getting close, but it didn't sound quite right in the HF on one channel or the other when we ran oxide coated tape, because the oxide tape would run at a slightly different relative height.
Speaking of visual alignment, something I really like about the 2 track heads we get from Greg Orton is that there are outer bands on either side of each track that are wide enough that when you are spot on you can see just a hint of the band one either side of the tape. That kind of indication makes it much easier to do the visual alignment. Unfortunately the Technics and Otari 1/4 track (or for that matter the 2 track) heads aren't like that, so there tends to be a litle more fiddling with adjustment to the head height when we run tones on them.
OK, I better get back to manual writing...
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On the level adjustments for 1/4 track prerecorded playback, I don't think that they have to be that terribly precise. In the process of working out the fine points on my Dolby mods, I've found that the levels from left to right channels on the tapes themselves range from a little off to way, way off. And that's on the best examples I have. I'm guessing that these are the result of a combination of the narrow track, storage related issues (temp.) and age/wear. The newer tapes that were produced on high speed duplicators have the added problems associated with country lane tape wander due to a combination of high tape speed (trapping air between layers of the wind) and poor tape slitting. I find many of the newer Ampex produced tapes (London, Phillips, DDG etc.) that are often on backcoated tape (which are prone to stick shed too) have levels that are all over the place. Some are recorded so loud that the tape brickwalls while others are so low that it's difficult to get a correct Dolby level set. It's really a shame since some of these sound fantastic in between these problems.
Because of these, I've just gone with making my own tapes with levels from the final tape checked with my software meters. I make them on an old Sony 1/4 track I have and I figure that as long as the levels are all equal to each other, I'm not going to worry too much about it. After all, it's probably better if the left channel has more gain then the right on most 1/4 track prerecorded tapes.
I'm finding that the trick here is working within the confines of these old tapes. And unfortunately, some of them will never sound good no matter what you do. Fortunately, if you're selective in the tapes you collect, they can sound fantastic.