Balancing Your Audio

If anyone out there is reading this blog but happens not to follow me on Twitter, first off, let me tell you you’re missing some gems.

But you will hopefully also be pleased to learn that due to an unexpectedly quick and overwhelmingly positive response to my last post, The Cable Bible has passed from a half-rhymed idea to a concrete project in record time. The bare bones of it are in place on the AMIA Open Source Committee’s Github page, and I will be trying to expand on it throughout the summer, adding more interface and protocol descriptions, images of connectors and pinouts, etc. If it’s a project you’re interested in, please contribute! Moving the guide from my own private Google doc to a Github repository was intended to encourage collaboration (I can’t catalog every single computer cable myself, dig?) – and if using Github overwhelms you (it IS intended mainly for software developers, and using it for documentation has its advantages but also non-intuitive kinks), may I direct you to Ashley Blewer’s terrific introduction to the interface?

But before The Cable Bible becomes a one-stop shop for all this information, I’ve already started to field a couple questions about cabling based on what I’ve learned over the past month or so. And one of the main ones, which I’d like to talk briefly about today, is the question of balanced versus unbalanced audio cables, and what the hell that means.

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Nope not that kind of balance

Balanced and unbalanced audio were terms that came up occasionally during my coursework at NYU, primarily in relation to setting up workflows for digitization of media on magnetic tape. But unlike, say, the difference between composite and component video signals, the difference between balanced and unbalanced audio was never really satisfactorily explained to us. That’s sometimes how it is when you attend a Moving Image Archiving program – due to to the constraints of time in an already over-crowded curriculum, some aspects of audio preservation can get short shrift, as if audio is a necessary evil in our quest to appease our visual appetites (we fully recognize this is something to improve in our program and the field at large – recently the Library of Congress hosted a conference regarding the work of its Radio Preservation Task Force, and the 10th Orphan Film Symposium in April celebrated how the history of film and the moving image is intertwined with the history of sound recording).

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But understanding balanced and unbalanced audio is a relatively simple concept, as it turns out, and worth understanding because from the outside the binary nature of the terms is slightly misleading, implying “good” and “bad” audio cables, when really employing either is perfectly acceptable given the right context.

Audio cables in general are susceptible to “noise.” No duh, right. But I’m not talking about noise in the general sense of “sound.” In audio cabling (whether a production, playback or preservation environment), “noise” usually refers to unwanted interference with the audio signal as it passes along a cable: an audible hum introduced by other electronic equipment or lights in the vicinity, minuscule snatches of radio and television transmissions in the air, etc.

Unbalanced cables actually contain two wires inside of them (and connectors that have two corresponding conductors each). One wire carries the audio signal, while the other is referred to as “ground” (and typically surrounds the audio signal wire in the center of the cable). The primary purpose of the ground wire is to shield the signal wire from outside interference, and in many cases it does a fine job of noise reduction. However, at other times, the ground wire can itself act as an antenna and start picking up unwanted noise itself. Typically the longer the cable, the more susceptible an unbalanced cable will be to noise.

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Balanced cables were introduced as a method of increased noise reduction. Instead of two wires, balanced audio cables contain three wires: ground, “hot” (the desired audio signal) and “cold” (a “negative” copy of the signal). The signal on the “cold” wire is exactly 180° out of phase of the audio signal – meaning if you were to play these two signals at the same time, they would theoretically cancel each other out, leaving you with silence.

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On the right, a “cold” signal with positive and negative peaks exactly the opposite of the original.

That seems undesirable. But what equipment designed for a balanced signal does is flip the signal on the “cold” wire back into phase at the point of input. This has two advantages: first, you’ve now theoretically doubled the strength of your audio signal, as the signals from the two wires will be perfectly the same at playback. But also keep in mind that any noise that was picked up as the signal traveled along the cable will be the same on both wires (not 180° out of phase with itself). So when the “cold” wire signal is inverted at input, the noise will now be phased out when combined with the noise signal from the “hot” wire. You’ve cancelled out the noise when the audio is played back.

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Image credit to these past three images from avion.com

 

Certain types of connectors make it easy to spot a balanced or unbalanced cable. XLR connectors are most common for balanced signals (you can easily see the three pins in an XLR connection, acting as the conductors for the ground, hot and cold wires), while RCA connectors will always carry an unbalanced signal, as they only have two conductors (the main pin conducts the audio signal, while the outer, round shield of an RCA connector is the contact point for the ground wire).

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More acronyms please I don’t think we have enough of those yet in media preservation

1/4″ and 1/8″ jacks, however, come in different flavors (TS “tip-sleeve” or TRS “tip-ring-sleeve”), and are also frequently used to carry stereo signals (all the discussion above relates to mono signals, where one cable is designed to convey one channel of audio; stereo cables can carry two channels of audio, which adds another wrinkle to the balanced/unbalanced issue). So you have to watch out with 1/4″ and 1/8″ jack inputs and cables, to be sure you’re conveying the signal you want. (There is no harm per se to using a balanced audio cable with equipment designed to use an unbalanced audio signal, or vice versa; the sound will travel from point A to point B either way, but you won’t get the noise reduction benefit of balanced cables used with balanced equipment).

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So many diagrams, so little time

Balanced cables are usually associated with professional setups, while unbalanced audio is frequently found with consumer-grade equipment – DVD and CD players, for example. But really, using either is just matter of how much you’re concerned about noise interference. For instance, in our digital audio workstation in the department, our former cassette deck (bereft of life, it rests in peace) only had RCA, unbalanced audio output. That might seem unideal for an archival digitization workflow, but given our setup the audio cable was barely traveling a foot to a patch bay; plus both the cassette deck and Wavelab software we were using for capture had built-in noise reduction capabilities. If we were more concerned with preserving the quality of these cassette recordings over the content, I might be concerned about using these features, but given at least that specific collection and this specific equipment, noise was not particularly considered an issue and unbalanced signal was perfectly acceptable.

For more lessons in audio cabling, keep an eye peeled on The Cable Bible – and maybe someday we’ll talk about optical cables, which is a whole different, flashy Tron-like ballgame.

Totally the same thing.

The A/V Cable Bible

Once upon a time, the cables in the MIAP lab were organized. I have a spreadsheet and everything to prove it. Video cables were neatly separated from audio-only cables, while patch cables and computer cables inhabited their own particular niches. Order and stability reigned.

Was it a long, slow descent into chaos over the years, as various staff, faculty and students picked one cable off from its carefully arranged post and then flung it back, willy-nilly, into the fray? Was I trolled by the Joker?

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Who can say. But for a while now, XLR cables have fraternized with 9-pin remote data controllers, USB 2.0 co-mingling with S-Video. Madness and miscegenation, I say.

It didn’t take long to wrangle our peg board cable storage units back into something resembling structure. Start from scratch, sort by type (video, audio, patch, data), make sure every single cable is at least adequately coiled and has its own tie, and we’ve made it so that at least I will be able to find, say, a 1/4″ TRS jack-to-male RCA cable if I so need one. The addition of labels to the peg board is nominally so that other people, too, might be able to find what they need without too much of a head-scratching search – but the truth is it’s just as much to scare people into realizing that there is, in fact, SOME sort of system in place.

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Progress, of a sort

Why am I talking about a minor organization project, that, really, only took about an hour of work? Well, this bout of spring cleaning inspired a sort of The More You Know moment – one of my attempts at self-education that comes (constantly) with the territory. With about 90% of the cables on the board, I was already familiar with their purpose and nomenclature – for instance, that a BNC-to-video-patch cable could be used to hook up the composite video output from one of our auxiliary decks (DVCam, S-VHS, Betamax, various formats that we don’t use enough to merit being mounted into our more permanent racks) into our digitization workflow. There were others that I had never used, and was somewhat flummoxed as to what equipment they were used with or even what kind of signal they were intended to carry. This one in particular was an old-school stumper:

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And also weighs about as much as a tree stump, by the way

So I started to write up a guide, originally intended for my own use. A Cable Bible, if you will, detailing all (or at least the most common) connections that I would have to make and some context for what kinds of cables tend to appear where. Because once I started looking up some of these things, I realized what a rabbit hole A/V cabling is. See, every cable you use in media production and preservation is actually a jumbled design of wire material, signal types, encodings and interfaces, physical connectors, etc. etc. You can say you have a hard drive you need to connect to a computer and you need a USB cable, but what does that really mean? Is the interface USB 2.0, 3.0 or 3.1? What kind of connecting port does the computer have – Type A? Type B? Type C? Or the hard drive itself – is its port Type Micro-A? Micro-B? Micro-B SuperSpeed?

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I mean this isn’t even comprehensive!

There’s also the fact that the standard for discussing cable connections is to differentiate between connectors with pins as “male” and connections with ports as “female.” For instance, in order to recently set up a DVCam deck for digitization, I needed a female RCA-to-male XLR adapter in order to get a male-to-male RCA cable to hook up with a female XLR port. Perhaps I’m just being phenomenally PC about this, but I’ve never cared for the way I sound vaguely like a pervy teenager when I’m just trying to make a video deck play. And I can’t help but think that only a historically male-dominated profession would decide to make such a common part of its work a giant dick joke.*

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I know archives are sexy but come on guys.

When all’s said and done, I hope the Cable Bible will be a shareable document, easily navigable by categories that consider the broad goals of the connections purpose before burrowing down into the specific protocols and connections necessary for particular equipment (with examples listed). Do you need to make a video or audio connection? If video, does it need to carry an analog or digital signal? If analog, is the signal composite or component? If component, how are the luminance and chrominance portions of the signal divided? Into two channels, Y and C? Then you’re looking for an S-Video cable, available with mini-DIN 4-pin connectors, or perhaps a SCART connector if you’re dealing with European equipment. Is it in three channels, Y, Pb and Pr? You’re looking for “component” cables, the more-familiar three-pronged cable(s) traditionally available with red, green and blue RCA connectors, though professional or broadcast equipment might require BNC instead (or, again in Europe, SCART).

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When it came to analog video, Europe was crazypants.

Or maybe the Cable Bible will let you work backwards instead: let’s take for instance, that mystery monster of a cable I found while reorganizing the lab. What we have at one end is an 8-pin monitor connector, and at the other, a 5-pin DIN and two UHF connectors. UHF was a WWII-era connection originally developed for conveying radio frequency signals (including video) within a certain range; DIN 5-pin had some applications in professional audio. 8-pin was a very specific protocol intended to carry analog video output and input over the same connection. So what we have here is likely a cable intended to carry both the analog composite video and analog, unbalanced audio signal back and forth from a very old video monitor to a very old video deck (at a guess, possibly 1/2″ open reel).

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An 8-pin monitor connection on the back of a Sony 3/4″ U-matic deck – I don’t have any equipment that would take the UHF/DIN end of the cable.

Even as I work on this blog post, the Cable Bible is spiraling slightly out of control in the Google Doc where I started it, as I add pictures and pinouts. It’s possible that this project would work better as some sort of Wiki, where one could more easily navigate the different layers that cables operate on and branch out to explore from there – others would also potentially be able to contribute and document more obscure or unique types of connections and protocols. Much of this information already exists on the internet, even on Wikipedia itself – but it’s a matter of consolidation and making it at least somewhat specific to archival context. I will update everyone if anything public develops!

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Something like this is just the start.

 

*Upon writing this I went back and remembered that I opened this very post with a fairly unnecessary, though (I hope) innocuous miscegenation joke. I’m keeping it in as this blog is meant to be an honest reflection of my thoughts, and this little contradictory exchange with myself is evidence that even self-reflection and good intention doesn’t change the fact that I am still a straight cis white man in tech and these are the sort of weird little obstacles that still mine the field for others.

 

Cassette Deck Repair, Round 2

When last I left you, dear readers, I was stymied in my attempts to transplant a broken gear in a Tascam 112MKII audio cassette deck with a healthy replacement. A few tiny, inconveniently placed screws were stripped such as to prevent getting to the heart of the matter (or the deck). I investigated some options for purchasing screw extraction bits for our power drill, and have indeed added those to my box of toys (*cough* I mean tools) since.

But I am not a patient man, which meant I went in for another round of futility because hey, what am I going to do, break the deck more? (I mean yes, I absolutely could do that but THAT IS NOT WHAT THIS BLOG IS ALL ABOUT). After failing at the so-called “rubber band method” (I just have a bunch of rubber bands with screwdriver-tip-shaped holes in them now), I took the suggestion of one of our Cinema Studies PhD candidates and applied a vice grip.

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Pictured: overkill.

Leverage was near-impossible when trying to turn a 3mm-wide screw with a giant vice grip at a weird 45-degree angle. Yet somehow, yes, I was able to loosen the stripped screw enough to get in there and manually twist the dang thing out. Surgery back on track!

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Before….
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…and after! Note that this is actually gear assembly cover removed from the “healthy” 122 mechanism, because I took that apart first because I do sometimes learn things.

Now able to remove the cover housing the gears for the playback mechanism, I could finally get to the clearly offending piece of the puzzle. Yes, it is difficult for your cassette deck to keep running when one of the delicate plastic pieces inside literally cracks in half:

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I know you guys might not know a lot about audio cassette decks but surprisingly this is a problem. Whoda thunk.

At first, since it was such a clean break, I did idly wonder if I could just super glue the broken gear back into place, and even made a quick stop at the hardware store around the corner over my lunch break (as is my approach to most tools or supplies, I tend to just try to buy whatever I can think of, under the assumption that even if I end up not needing it now, it will almost certainly prove useful at some point later). I don’t know how archivally sound the combination of Krazy Glue adhesive is with whatever plastic this gear is made out of (it almost surely wouldn’t have held up for another couple hundred tapes), I realized that the point was kind of moot, because even past the obvious, giant chunk of the gear that had snapped clean off, less noticeably the teeth on the smaller inner part of the piece had also been totally worn down, and were also likely not catching properly in the mechanism.

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The cassette deck just CASSETTED SO HARD this gear couldn’t take it

So, back to the replacement part then. Going back over I tried to take out the healthy gear from our backup 122MKIII…

…a process that literally took about 30 minutes. See, all I had the do was lift the gear out – but whatever lubricant had been placed on the gear shaft of this deck had morphed, over years of disuse, into a pretty strong adhesive. That gear was stuck tight, and, considering the broken-in-half example right at my disposal, I had a hunch this piece was kind of fragile. It would be pretty useless to snap a gear while in the middle of replacing a snapped gear, so I had to be extreeeemely patient and just ever…so…gently…wiggle the gear off the shaft, most of the time never apparently doing anything at all (in fact, if it hadn’t been for the fact that the broken gear lifted out so easily of the 112, I probably would’ve assumed I was doing something wrong with the intact one).

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Now stop – Wiggle Time.

But, once that finally came free and I took a minute or two to revel in the satisfaction, I was finally able to piece back together the gear assembly on the 112, and a few manual turns seemed to confirm that the motor would now spin correctly. By all outward appearances, this was a successful transplant and I hurriedly packed the tape transport unit back into place to test my handiwork. For one brief, shining moment, as I pressed the Play button, the motor whirred, the gears turned, and all sounded healthy as the tape started moving forward at normal speed and the meters bounced.

Then a second later, the head assembly kicked out of playback mode. Trying again, the same thing: playing back fine for a second, then the system automatically refused to keep going.

Sigh.

Unlike last time, there were no hideous noises emanating from the deck, and the lights on the transport buttons on the front panel were not freaking out. The lights on the programmable buttons (RTZ, LOC1, LOC2, etc.) were now constantly on – but I could not tell when exactly that had happened, and in any case they still appeared to be responsive (I could set a zero location, fast-forward the tape, and then automatically return to that location, for instance). So that seemed unrelated to the tape refusing to stay in playback mode.

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After a few more repeated tries I still couldn’t figure out what was happening, so I hit eject to remove the tape and take another look at the transport mechanism in case I missed something – which is when I saw this:

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Bad tape! You’re not supposed to stay outside your cassette past curfew. You’re grounded!

Hmm. Why was the tape loose in the cassette? Winding the tape back tight (oh how long has it been since I had to manually wind a cassette with my finger? too long, for this ’90s kid), I took a closer look at the cassette itself as I attempted playback. At which point I saw that when I hit Play, the supply spindle (the side of the cassette on which the tape is wound) on the cassette would start spinning, but the take-up spindle (where the tape winds after passing over the heads and playing) refused to budge – meaning that after passing over the playback head and through a pinch roller, the tape would just sort of loosely dump into the cassette for a second or two, until the pinch roller presumably detected that it had lost tension and automatically kicked the head assembly out of playback mode, to protect the cassette and the deck from getting damaged by out-of-control tape.

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And that, essentially, is where I am stuck right now. The take-up spindle has no obvious motor driving it, and I am pretty confident I didn’t damage that part of the transport unit during disassembly – although, given the fact that the 122, which I am essentially using as a model of what the mechanism on the 112 should look like, doesn’t spin at all, I can’t say that for sure. So why is it not turning during playback? The only thing I can think of is that somewhere in the transport unit is a sensor that communicates with the take-up spindle that I somehow mucked up – although, again, the spindle turns completely normally during fast forward and rewind. And if I actually sit there and manually spin the take-up spindle, playback continues normally. But that is not exactly the most practical solution, since I have, you know, at least some other work to do.

If anyone has further suggestions, I’m all ears, but at this point I’m further investigating backup decks and probably bringing in a more experienced audio technician to perform a repair – at this point I would at least have a very specific issue to bring to them, which would hopefully keep the repair quick and therefore relatively inexpensive, since freelancers charge by the hour.