Balanced Audio.
 
Well, here's a subject I ought to know a bit more about...
...but do I need to?
 
My home setup is quite modest:
 
A PC (with SONAR) and a soundcard with stereo lines in and out.
These go into a patch-bay before going into a main mixer (rack-mount, 12 channels) and then on into the amp.
 
Also going into the patch-bay are various noise-making devices such as a synth, electronic drums, guitar FX processor and some other devices like an old cassette desk, VCR, DVD etc that I use for mastering or digitising some of my older material.
 
The main input chain for vocals is a condenser mic into a Joe Meek pre-amp (using XLR). This is chained into an EQ rack and a compressor by using the patch-bay to send the output of one into another, lining them up so they default into one another without needing to use patch cables.
 
In fact, most of the convenient connections are directed straight into mixing desk channels via the patch-bay so, most of the time, I don't need to patch anything manually.
 
Thanks for indulging me so far... nearly there...
 
Apart from the XLR cable which connects mic to pre-amp, EVERYTHING else I use is a mono jack lead, ranging from 2 feet long to 10 feet long depending on where they are in my room. Most of the spaghetti sits behind the rack where I have the mixing desk, patch-bay, amp and all the other bits I mentioned above.
 
I often read about BALANCED connectors. It appears that I'm not using any.
Should I use any? What am I missing out on here? Noise reduction? Hum and whine?
 
The only noticeable interference I get is when I connect my Ovation acoustic to the Joe Meek preamp using an XLR cable.
I get a terrible 'tuning an old-fashioned radio' squealy-whine which a can never fully stop. (I usually either gate it off or remove it later with a software noiseprint-subtractor).
 
If I DO switch to balanced, is it simply a case of replacing cables with the 'stereo-jack' type leads or is there more to it?
 
Can anyone tell me whether I'm making a mistake by not using balanced connections?
My recordings sound pretty good to me but I can't help thinking I'm missing something.
 
Thanks in advance...!
 
Frink.

If that is a "modest" set up, then I guess mine must be spartan.
 
With regards to the squealing with the Ovation into the Joe Meeks - are you connecting it to a high-Z (instrument) input.  I'm guessing you are not since you are using an XLR.  This is causing an impedence mismatch that may be causing your squealing.

"Balanced" doesn't just apply to the connectors, but also to the electronics at both ends of the connection. IOW, having balanced connectors won't do you any good unless the sending device has a balanced output and the receiving device has a balanced input.
 
It's not always obvious whether a given device has balanced inputs and outputs, since they look the same from the outside. You'll have to refer to their documentation to find out for sure. So the first step is to identify which of your devices are balanced. If none are, then the question is academic.
 
Devices that typically are NOT balanced include synthesizers. The only synth I've ever owned with balanced outs provided them via XLR connectors, clearly labeled "balanced", so there was no guessing. If you just have a pair of quarter-inch phone jacks odds are they're unbalanced.
 
Which is why DI boxes are typically used with synthesizers, as they'll convert unbalanced to balanced. If you're picking up hum from synth cables, going through a DI box will usually fix it. You'll want to place the DI close to the synth with short cables going to it, so that the longer run uses balanced cables. (Of course, if the hum is generated internally in the synth's power supply you're probably stuck with it.)
 
If you're currently using unbalanced cables with balanced devices, you're guaranteed a poorer SNR. Not only because the signals aren't balanced, but also because they're at reduced levels. 

(a couple folks here knew I'd rise to the bait...)
 
Balanced, for audio, refers to the respective impedance to ground from each of two conductors. In order for a circuit to be balanced it must have a balanced source, two conductors, and a balanced receiver.
 
There are tons of myths, and a fair amount of misinformation, but that's what it's really all about. There is no requirement for signal on both conductors, it has benefits, but it is not required.
 
So except for figuring things out, there isn't a tremendous utility to talking about balanced cables, balanced inputs or balanced outputs. You must have all three to have a balanced system or circuit. No cheating allowed<G>!
 
As an aside, the whole bit about signals of equal amplitude and opposite polarity (NOT PHASE) is referred to as symmetrical, not balanced. You need two conductors for both, and it makes sense that a symmetrical signal needs a balanced circuit... but they are not the same thing.
 
Back on topic, so you can drive a balanced input from a source that has a signal on only one conductor. You'll sometimes see this referred to as either impedance balanced or pseudo-balanced. It is, in fact balanced if, and only if, the impedance from each conductor to ground is equal.
 
When the signal gets to the balanced receiver or input what happens is a sum & difference trick. The receiver accepts the difference between the two conductors (differential mode) and cancels any signal that is common to both (common mode). You will see this referred to as Common Mode Rejection Ratio (CMRR).
 
Which leads nicely to the next point. In order for a balanced input to work well we need to expose the two conductors to exactly the same fields. This can be accomplished with a spaced pair, but it can be better accomplished with a twisted pair. Since the two conductors constantly (and hopefully uniformly) trade places, any magnetic fields will be imposed on both conductors equally. That means that the voltage impressed, and the resulting current flow, will be equal. And if they are equal we can cancel them out easily.
 
Am I making sense so far?
 
So what about shields and grounds and all that other stuff?
 
Shields are almost useless for magnetic fields (and power line noise propagates via magnetic fields). Shields are useful for electrical fields... but in order for them to be effective they need to be grounded at both ends. And we all know about the evils of ground loops.
 
For now I am going to simply point out that the ground reference is entirely unnecessary - the signal is derived from the difference between the two signal conductors.
 
I don't know if this helps you figure out what you want to do or not, so I'm going to stop now and let you digest. Feel free to fire back with questions as they occur to you!

Which is better for CMMR at the inputs? Precision matched resistors and laser trimmed transistors or a cheap transformer?
  
I imagine that I'm about to learn what i didn't know as I learn what I should have known before I spoke up as if I know something. ;-)

mike_mccue
Which is better for CMMR at the inputs? Precision matched resistors and laser trimmed transistors or a cheap transformer?

 
That's not really a valid comparison... or perhaps I do not understand the question?

So, if I were designing a differential amplifier as the first stage of an audio device I'd take the following into consideration:
1) Headroom - man you can't believe the difference a little extra headroom can make. Actually, you probably can<G>!
2) Bandpass - eventually you probably want to make it reasonable, I've never really figured out where.
3) Noise Rejection - which is what you are asking about.
 
So, the input impedance presented to each input pin needs to be identical -
 
you can do that with precision resistors AND matched transistors,
 
you can do that with well matched dual op-amps AND the precision resistors
 
you could skip ahead five spaces and just use the THAT Corporation InGenius chips, but yes, you still need those precision resistors
 
you could stick a transformer (but not a cheap one) in front of whatever you designed.
 
All other things being equal (which of course they aren't) the transformer will provide higher CMRR than pretty much any other topology. But there are drawbacks - good transformers are expensive, and depending on the signal level, they can be quite large and heavy. And they behave like inductors, or rather, the primary winding is an inductor, so you have increasing impedance with decreasing frequency. There are transformers that can pass +26dBu with minimal attenuation, but they are huge, and very expensive.

For line level designs I've pretty much settled on the InGenius chip. The performance is excellent, the cost is reasonable, and the only thing I really give up is galvanic isolation, which should not be a huge problem if I've done everything else well at the system level.
 
Sadly (or not), the chip is optimized for line level signals, it does not work well with microphone level signals. And it doesn't behave terribly well - or doesn't provide a big benefit - if it sits behind a gain stage. Beside, you'd have to match those gain stages really well!
 
For microphone level designs I am learning that there are lots of topologies that can provide the gain, headroom, bandwidth, noise rejection, and S/N ratio I'm after, and each of them sounds a little bit different. I'm not sure why that comes as a surprise!
 
One last thought - you did not mention capacitors. In my limited experience these are the biggest troublemakers! Even precision capacitors are not all that precise, and you really don't want them in the signal path (at least at audio frequencies) at the front end. Unfortunately, if you are designing a microphone preamplifier you need a way to block the phantom power (well, you could use it as a bias I suppose), and that means capacitors or a transformer. And putting DC across a winding isn't always the best idea either.

So I guess I didn't really answer your question... sorry about that!

"One last thought - you did not mention capacitors."
 
Can I say that I was pretending phantom power didn't exist?
 
 
"I guess I didn't really answer your question... sorry about that!"
 
Ah... but you did:
 
"All other things being equal (which of course they aren't) the transformer will provide higher CMRR than pretty much any other topology."
 
Good times!
 
:-)
 
I am slowly learning more about balancing every time you rise to the bait.
 
:-)
 
Thanks.
 
best regards,
mike

@Bill:
You do not need a "balanced" source. If e.g. your synth has an unbalanced output (tip and sleeve) and your audio interface has a balanced (XLR) input, you can reap the benefits of the balanced input by using a cable as described here: http://www.rane.com/note110.html under 13. Note that this is the 'ground lift' version. You can tie 'cold' and ground together at the unbalanced end as shown in Fig. 15 here: http://www.douglas-self.com/ampins/balanced/balanced.htm In either case, you need a shielded 2-conductor cable. Otherwise, you give away all the benefits.
 
Hi Frink:
Yes, balanced is better. However, if you don't have long cables and you don't have issues with hum and buzzing noise, you can get away with unbalanced cables.
As Dave pointed out, your only problem seems to be your Ovation guitar. If your guitar has a piezo pickup without an active (battery-powered) preamplifier, you have a problem. You would need a high impedance instrument input. An excellent alternative is a preamplifier that you can integrate into your guitar. You will need the help of a luthier, though. http://www.ebay.com/bhp/ovation-guitar-preamp
 
Also, audio interfaces with balanced inputs (including high impedance instrument inputs) have become so cheap that buying a new interface that replaces the patch-bay and your mixer may be the cheapest option. That said, you will need to buy new cables, if you choose this route.
 
Wilko
 

FYI Dave there are few synths that do feature balanced outputs but not on XLR but rather TRS. One is the later Kurzweils PC2x and PC3K (mine) Older K2000's are not balanced unfortunately. Another is the EMU Emulator 4XT and E5000. Also TRS connectors and fully balanced.
 
SOOOOO yes you need to check the documentation to actually know for sure.
 
And my Samson analog mixer has balanced stereo line inputs also via TRS and at first I tried connecting my Kurzweil via unbalanced leads and it worked OK. But it was a little noisy (when not sounding) When I connected via balanced shielded leads the difference was quite apparent. Way more signal and the noise gone and I mean totally gone. Literally dead silent now.
 
It can make quite a difference with some instruments but your patch bay would have to balanced as well. (is it?) and the inputs would also need to be balanced.

Cakewalk User Forums: Better than Wikipedia.
 
I'm just going offline for a couple of days whilst I process the information that you've all given.
 
Thanks everyone - responses were exactly what I was hoping for. You guys are so good  <*sniff*>
 
F.