"Pro" VCR with XLR audio output: I'm stuck

[Brad]

I bought a VCR that has only balanced XLR audio outs with the exception of a headphone output (which apparently only monitors one channel at a time). My capture cards have only unbalanced RCA inputs. Is there any cheapo solution to this conundrum?

[hech54]

http://www.bhphotovideo.com/c/buy/RCA-to-XLR-Cables/ci/4201/N/4294545160

[Brad]

I realize that will make the physical connection, but will it do whatever electrical change is involved in making balanced into unbalanced?

[Cornucopia]

No, you are right. That kind of cable does little to change the signal from balanced to unbalanced and it does nothing to adjust the level.

You would need something more along the lines of this:http://www.markertek.com/Audio-Equipment/Audio-Processing/Audio-Hum-Noise-Eliminators/...RT-CLEANBOXPRO

Scott

[Brad]

An electronics shop and a music shop both told me that balanced/unbalanced goes along with XLR/RCA, it doesn't matter, and that straight adapters or cables will work fine. The only downside, the music shop said, is that you don't get the benefit of balanced. I bought a couple of the adapters.

My initial captures came out clipped, even with the adjustment on the back panel set to -6dB (other options being 0dB and +4dB).

The VCR also has pots on the front for playback level, luckily. The only downside is that it's tricky to get the little knobs for both channels to match. Well, that and it's annoying to have to carefully watch that I don't brush up against the knob and mess up the audio.

[Cornucopia]

So clearly, the people in those shops who talked to you were NOT audio engineers like myself, but rather salespeople who know nothing about the actual nuts & bolts of audio, and just want to sell you someting or placate your ego.

They are wrong on so many counts.
It's true, RCA is ALWAYS unbalanced, but incorrectly XLR can be either balanced or unbalanced (and balanced can be other things like TRS 1/4"). And it DOES matter a great deal. Straight adapters don't just work fine, which you found out the hard way. Were they willing to refund you the price of those cables? I doubt it.

The level difference alone (not counting the other, important things) between your standard RCA (unbalanced, high impedance, consumer line level @ -10dBV) and pro XLR (balanced, low impedance, pro line level @ +4 dBu) is ~12dB (not 14, as the scales of V and u are different). So dropping your source output levels to -6dB still would have made it ~6bB too hot for your inputs. I could go on, but I won't. Hate to say I told you so, but...

Scott

[Brad]

The adapters cost under $10 total for two, with 12% tax. I simplified their explanations of course; XLR being both potentially did come up but since we know from the manual this one only outputs balanced...

All of this information would have been useful in your original response, including the bit about being an audio engineer!

I actually saw almost that exact CleanBox model in a pawn shop or someplace for a great price, but I didn't pick it up since I wasn't sure whether it was really required. Plus I didn't want to have more knobs to fiddle with and yet another AC adapter chained to my power bar.

Some sort of resistor or whatever that would just cut -12dB from the signal would be ideal. A solution that doesn't allow any variability.

[hello_hello]

A balanced cable uses the original audio signal, a phase reversed audio signal, and ground. The idea behind doing it that way, is rather than send the signal down the cable for it to be amplified etc as would happen when it's unbalanced, the difference between the two audio signals is used instead. Then if electrical interference happens along the way, it'll effect both of the audio signals by the same amount (or roughly), the difference between the two remains the same, and the actual audio is in the end, hopefully unaffected. The same principle is used for other applications such as ethernet cable and telephone lines etc.

There's two ways to wire a cable when going from balanced to unbalanced. The "correct" way is to connect the positive wire from the XLR to the positive on the RCA. Both the negative signal and the ground pin from the XLR are then connected to the ground on the RCA. The positive pin on the XLR should be pin 2, negative is pin 3 and ground is pin 1. Some older equipment might use pin 3 for the positive signal instead of pin 2, but it doesn't matter too much. As long as one of the signal pins goes to the positive pin on the RCA and the other to ground.

You could try disconnecting the wire going from the negative signal (pin 3) on the XLR and leaving just pin 2 going to positive on the RCA and pin 1 going to ground. Generally when going from unbalanced to balanced it'll reduce the level a fair bit but I can't remember if it has the same effect when going in the other direction (balanced to unblanced).

The problem is probably that "pro" equipment and "consumer" equipment often uses different line levels, and "smi-pro" equipment often has a switch to switch between output/input levels, but without one the audio can end up being either too loud or too quite, depending on the direction it's going. It's not really a balanced/unbalanced issue at such http://en.wikipedia.org/wiki/Line_level
If that's the case, then a device which lets you adjust the level between two connected devices might be the only solution. The capture card doesn't have an option to change the input level? Mine does or you can use the appropriate level in Windows own Volume Properties thingy, or both. between the two if them they might drop it enough, although there's no guarantee the input won't be distorted no matter how much you reduce the input volume.

[Cornucopia]

To clarify: The idea is [Signal] - [-Signal] = 2xSignal, but ([Signal]+Noise)-([-Signal]+Noise) = 2xSignal + Noise - Noise = 2xSignal.

And the ONLY "correct" way to go from balanced to unbalanced or from unbalanced to balanced is with transformers and/or isolating op-amps in-between.
***If you do not do this, you've basically negated the "balanced" section and it acts just as if it was unbalanced, losing any noise benefit you thought you had.
And ONLY the iso op-amp method also takes care of the ~12dB difference in signal level (either going up from consumer to pro, or going down from pro to consumer).
Also, that kind of adjustment should best be done while still in the analog domain.

@OP, I told you what you needed. If you didn't believe me, you could always have posted again with questions, or looked up my (large) body of previous posts on it and many other subjects to see that I knew what I was talking about. I shouldn't have to start each response with my credentials.
Plus, there's plenty of other clear, audio engineering-based sites that confirm what I've told you. You could have followed those as well.

A 12dB resistor is not the ideal option (what have I been talking about!!?), but you seem stuck on avoiding the correct, suggested method.

Scott

[Brad]

If you didn't believe me [...] I shouldn't have to start each response with my credentials.

Didn't believe you? I was the one who suggested the idea that the adapter wasn't enough to begin with. So much for placating my ego!

Besides, you already type "Scott" at the end of each post. Would it be that much more work to type "Scott / Audio Engineer" instead -- or better yet put it in your signature?

Plus, there's plenty of other clear, audio engineering-based sites that confirm what I've told you. You could have followed those as well.

I'm sure you know where these are, but I as an uninformed consumer just searched and searched and only found: overly-technical jargon that was of no help, people telling me the same thing as the salespeople told me, and people mentioning this CleanBox specifically without addressing how it actually solves the problem (or what the problem is).

A 12dB resistor is not the ideal option (what have I been talking about!!?), but you seem stuck on avoiding the correct, suggested method.

Because as I said, I don't want to have even more knobs to twist when all I need is an across-the-board reduction in level (apparently).

[hello_hello]

And the ONLY "correct" way to go from balanced to unbalanced or from unbalanced to balanced is with transformers and/or isolating op-amps in-between.
***If you do not do this, you've basically negated the "balanced" section and it acts just as if it was unbalanced, losing any noise benefit you thought you had.

There's no real noise benefit in this situation. The main difference would be, by wiring a cable as balanced to unbalanced you have no noise benefit at all, but if you stick a transformer in between them, the balanced side has more resistance to noise than the unbalanced side, but in this situation it's hardly likely to make a difference. It's really (for example) 2 feet of unbalanced cable vs 1 foot of balanced plus 1 foot of unbalanced.

Of course having something in between will help with the level issue.

[Brad]

I did end up finding that Cleanbox again; it was a Craigslist posting for $20. So I picked it up. The guy had a whole rack of analog transfer stuff that he no longer had a use for, but it was pro gear like U-matic and Betacam SP.

The only advantage I see to the Cleanbox is that I don't have to ensure my two knobs are in the same place so as to keep my stereo channels at the same level. It just has one knob that affects both equally. But I have the disadvantage of more wires snaking around my small workspace and another wall-wart.

I have placed the slider at the back of the VCR to the 0dB position again (-6, 0, +4 are the options). Is this "correct"? The Cleanbox inputs say +4dB which is confusing me.

Thanks to all who have contributed to this thread.

[Hoser Rob]

Cornucopia is right about pro gear v. consumer gear levels, and you're just lucky your machine has input level controls.

I've seen this sort of thing in a rack preamp for bass players. The effects loop output was studio +4dB level and it would overload many effects pedals, which are designed for lower signal volts than rack gear.

[hello_hello]

I have placed the slider at the back of the VCR to the 0dB position again (-6, 0, +4 are the options). Is this "correct"? The Cleanbox inputs say +4dB which is confusing me.

http://en.wikipedia.org/wiki/Line_level

If the VCR slider switches the output level (-6db, 0db and +4dB) then I'd assume you'd want to set it to +4db to match the input level of +4db.
If that's what it does I'm a little surprised the -6db position didn't work okay when the VCR was connected directly.

[Brad]

Didn't realize until I read your post that both devices feature "+4dB". Somehow I got it in my head that one was -4 and the other +4.