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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
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26th Jul 2022, 9:28 am | #1 |
Dekatron
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Wow and Flutter Testing
For quite a long time I have been intending to do some W & F tests/measurements on various tape decks using my Philips PM6307 Wow and Flutter Meter plus compare results with results obtained using the WFGUI application.
I do not have any tape speed/W & F test tapes, proper reference tapes are not that easy to find and can be pretty expensive (such as the MRL tapes). There are less expensive home made cassette speed test tapes online to order. Is there any major reason not to use a good quality 3kHz / 3.15kHz home recording tape done on a good machine at least for initial tests ? David Last edited by DMcMahon; 26th Jul 2022 at 9:36 am. |
26th Jul 2022, 10:25 am | #2 |
Hexode
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Re: Wow and Flutter Testing
If you use an existing home machine to create the tape you will be adding it's wow and flutter to any other machine you use it on and it will therefore give very spurious results.
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26th Jul 2022, 10:49 am | #3 |
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Re: Wow and Flutter Testing
You can of course make rec/rep combined measurements simply by recording the meter tone output and then playing it back. This figure will drift about as rec and rep wobble go in and out of step. It won't tell you anything about absolute speed, though. Reference tapes have good reason to be expensive.
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26th Jul 2022, 4:36 pm | #4 | |
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Re: Wow and Flutter Testing
Quote:
David |
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26th Jul 2022, 4:38 pm | #5 | ||
Hexode
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Re: Wow and Flutter Testing
Quote:
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26th Jul 2022, 4:47 pm | #6 |
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Re: Wow and Flutter Testing
Indeed, the reference tape has to be made on a machine which can be trusted to be significantly better than the machine you're trying to test, so that if you see W&F, then you know where to attribute most of it.
But just a minute, how was that much better machine tested and proven? Using the same logic, it needs a better machine to prove it, and that needs a better one still, and so on. As Terry Pratchett said "It's turtles all the way down" Impossible, so there has to be a way of breaking out of the loop and qualifying a low W&F machine without having to rely on a better one. A technique which uses the same machine twice and knows that the apparent W&F on replay can only come from the machine, and that equal amounts were added in recording and in replay would fill the bill. This is a common issue in test and measurement equipment. So you design some super duper measuring instrument better than anything that went before it.... so how do you calibrate it? You have to get wily and concoct a method traceable to first principles that has lower errors and doesn't need a better instrument of the type you've just designed. This can be as big a task as developing the instrument itself. David
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26th Jul 2022, 5:05 pm | #7 |
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Re: Wow and Flutter Testing
At Sony we only used Sony test tapes, due to the frequency of use some were often replaced at regular intervals.
Lawrence. |
26th Jul 2022, 6:18 pm | #8 |
Dekatron
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Re: Wow and Flutter Testing
The two concerns of which I have knowledge (BBC BH test room and MRL) use the best transports they can lay hands on - the BBC used to use the Telefunken M10A which takes up lots of room in my studio and went from that to an A80, I think, and MRL used A80s as well. Zero wow on a test tape is unattainable, of course, but these machines could consistently deliver around 0.02% under the right conditions, with a similar order of speed accuracy. The stability of the tone generators feeding them was also closely watched.
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27th Jul 2022, 1:17 am | #9 |
Tetrode
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Re: Wow and Flutter Testing
Hi,
You can purchase a suitable test tape from, https://dupeshop.com.au/test-tapes/ I've purchased several, both the quality & price is great. For most domestic cassette decks these tapes are more than adequate. |
27th Jul 2022, 12:14 pm | #10 |
Octode
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Re: Wow and Flutter Testing
When I worked for the BBC in Technical Services(Radio) as a maintenance engineer we were issued with our own set of test tapes from the BH Test Room and had to guard them with our lives. When I left they made sure we handed them back. They couldn't be fussed about what happened to the rest of our tool cases, only the test tapes.
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27th Jul 2022, 12:37 pm | #11 |
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Re: Wow and Flutter Testing
Try placing a wanted ad on here. You never know what might turn up. No cost, no loss.
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27th Jul 2022, 3:51 pm | #12 |
Octode
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Re: Wow and Flutter Testing
Were reel test tapes ever made with digital bins? I don’t imagine they were, as the bins were designed in the late era of cassette and the commercial imperative would’ve been non-existent.
I would be very careful WRT buying test cassettes. They should be made using a specially adapted reel machine with a full-track head. Most of the tapes seen on Ebay are made simply using a Dragon or CR-7, which has been checked with a Teac / Sony reference tape. If you’re using a tape made on another machine, don’t expect to have meaningful values. If you have a reference machine that you know checks out to 'x' RMS W+F via an MRL or whatever, and your homemade tape shows 'y' in that machine, then if other machines get near that 'y' value with the same tape, their W+F ought to be decent. But the value won’t mean anything in the real world. Does anyone know if the Sony / Teac test cassettes were made using digital bins? In theory, a digital bin ought to have W+F that’s virtually immeasurable. But they weren’t commonplace until the late days of cassette, and I’m not sure if the big guns were making test cassettes at that point. There is a fellow in Germany who sells a full set of cassettes for 35 Euros, made on an A80: https://www.luckyx02.de/kalibrier-ca...anspeter-roth/ If you Google ‘Hans Petter Roth test cassette’ you’ll get discussions about them. They aren’t flawless (he doesn't have Sony's budget), but they will get you 95% there. I use them regularly and they’re an absolute bargain (about the only bargain in the world of tape these days...). I have a Teac tape for absolute values. I’d get the HPR tapes while he’s still selling them. He sells on Ebay as well. Don’t get the Ebay ones made on Nak decks (pricier than HPR and inferior). I have been trying to persuade a friend to cut a vinyl test disc, with little success. He believes that a test disc is the absolute highest achievement of any cutting engineer and wants to do one before he retires, but believes it will be an enormous strain on resources to get right. I was once told by the great S W Davies that Ortofon spent well into 6 figures producing their test disks… Funnily enough, my tape machines outperform any of my quartz-locked DD turntables for W+F. Darn hole centering! |
27th Jul 2022, 4:02 pm | #13 |
Dekatron
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Re: Wow and Flutter Testing
I have seen a couple of references to digital bins/digital loop bins in older Threads but unsure what they are, can you please elaborate a little.
David |
27th Jul 2022, 11:18 pm | #14 |
Octode
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Re: Wow and Flutter Testing
Digital loop bins were used in cassette duplication. With standard loop bins the source was a long tape loop which was copied onto a pancake of cassette tape. The pancake was long enough to record multiple copies of the material - hence the use of a tape loop. After the pancake had been recorded, the tape was cut at the boundaries between copies, leader tape added and then it was loaded into cassette shells. All this happened at something like 32-64 times the normal play speed.
With digital loop bins, the source material was contained in digital memory. I'm not quite sure why digital loop bins come into this though - surely it would have been more sensible to use a precision signal generator to generate the test tones. |
28th Jul 2022, 12:42 am | #15 |
Octode
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Re: Wow and Flutter Testing
A quick scan of the TH site came up with this (much as what James said): https://www.tapeheads.net/threads/di...oop-bin.96651/
(Willhelm is ex-BASF btw) I mentioned digi loop bins as they are - to my understanding - what should be the ultimate way to make a test cassette, as the W+F should be non-existent. A W+F tape will always be limited by whatever machine is used to record the tape. I was going off at a tangent TBH. I am interested to know if they were ever used to make test tapes? I've never recorded a tone, played it back and measured W+F. I might try it out of intrigue. The best machine I have gives 0.03 RMS with a Teac 3150 tape. The HPR test tape I mentioned earlier gives about 0.04 with the same machine (apparently, the HPR shells aren't great - so using better shells could improve W+F and azimuth). I think that whether you have a pro-made test tape or make something yourself, if you can get a reading below 0.1 then the chances are W+F will be inaudible. An important feature of using a test tape in my mind is knowing that the machine's near factory spec. If it's noticeably off-spec, then something could be straining / heating / wearing out faster than it should. Considering how rare spares are for most machines, if you have a nice one, you want to take care of it. |
29th Jul 2022, 12:12 pm | #16 |
Pentode
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Re: Wow and Flutter Testing
For your info: During 70s, B&O produced an excellent disk for testing vinyl disk reproducers at that time. The STEREO TEST AND DEMONSTRATION as it named.
High quality music samples were included as well as several test signals. W&F test signal at 3150Hz was also included in the disk. Take a look at the attachments.
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29th Jul 2022, 3:29 pm | #17 |
Octode
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Re: Wow and Flutter Testing
Thank you, John. I shall keep an eye out for that one (it appears to surface on secondhand sites).
I wonder how much variation you'll see between pressings? |
29th Jul 2022, 10:33 pm | #18 |
Dekatron
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Re: Wow and Flutter Testing
Later BBC test tapes were made from a digital source - sinewaves of the correct frequency and amplitude were then on tap, but poor Douglas Smith sounded as if he was announcing the test bands down a 'phone line, and a rather crummy line at that. Memory cost money then...
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29th Jul 2022, 10:47 pm | #19 | |
Dekatron
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Re: Wow and Flutter Testing
Quote:
Main commentary is by Jack de Manio, which is a name from the past. David |
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30th Jul 2022, 8:47 am | #20 |
Octode
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Re: Wow and Flutter Testing
The limit with test discs is ultimately how accurately the centre hole is punched.
Some time ago I wrote an audacity plugin which allows you to visualise the wow and flutter components, see: https://www.vintage-radio.net/forum/...d.php?t=127882 Note input file must be mono. |