In what way are balanced lines +6dB "hotter"

T

Tobe

Simon
Hi all,
This is my first post, I’m from OZ, try to write songs, mainly guitar based with an old Fender Jag.

I am in the process of upgrading from a stock card (X-fi) to to an E-MU 1212m on my home Studio. So far so good. I have an old pre-amp with balanced outs and with a few test takes the quality improvement is pretty obvious.

What is bugging me is that the E-MU manual says a balanced system is +6dB “hotter” than an unbalanced system, but doesn’t explain what this means.

I get the idea that a balanced line runs a inverted double of the signal to cancel noise, and I have a vague notion that doubling up on the signal will increase the dB, but when it is going into an AD converter that will clip above 0dB anyway, what does +6dB mean?

Does it mean I can crank the same levels as an unbalanced setup and expect a +6dB louder signal but with the same amount of noise? Or is it just notional crap?
 
An electrically balanced output will increase signal level by 6dB. Let's say you have a signal that is 3V (really the voltage changes constantly, but play along). An electrically balanced output will take that output signal and invert it to -3V. Then it sends both those signals down the line to the next bit of kit.

The receiving amplifier is differential, which means it will output the difference between its two inputs. The difference between 3V and -3V is 6V, so your signal is now 6V, which is 6dB hotter than 3V, according to this formula:

dB = 20 * log (6 / 3)

Note that only electrically balanced outputs do that, the other two types of balanced outputs (impedance balanced and transformer balanced) do not.

Also, the 6dB increase becomes self-limiting because if there were no other gain changes made then each bit of kit would have to have 6dB more headroom than the previous bit--which is not realistic (even if manufacturers knew the exact order of your chain, which they cannot). So when you have an electrically balanced output, you will usually have to compensate by reducing level somewhere.

Depending on where that happens it can actually degrade signal-to-noise, but it's a small enough change that it probably doesn't make a noticeable difference. Generally, noise is dominated by earlier stages, so the electrically balanced output's noise contribution should be negligible. However, if you run into a headroom problem at the receiving gear, it's ideally best to reduce level in between them, or at least at the output of the earlier device rather than its input.

Again, probably doesn't make a noticeable difference. Just plug things in and enjoy . . .
 
Thanks mshilarious

Thanks mshilarious,

It seems you are suggesting that it is a notional gain. I suppose I will just have to make do with the DI bass tests I've done sounding much richer. :)

The balanced card does sound better, but on a few brief tests I've done to adjust for latency I've noticed that if I take a physical out and record it back in, it doesn't seem to digitally mirror the original as accurately as an unbalanced line.
 
That's odd; the unbalanced loop should be slightly degraded by interference. Anyway, since the unbalanced out is still feeding the same balanced input (just with one leg grounded), if you observe a degradation in the balanced loop I would imagine that is down to the headroom of the input. Try comparing balanced out at -6dB to the unbalanced (in other words, match levels at the input).
 
I should add, I'm in the Very early stages of coming to grips with my new system mshilarious.

On the old X-fi I stuffed around for ages before figuring out how to re-record (and adjust for latency and levels) so that the original and the copy would match quite well (almost cancel on inversion).

I go to all this trouble because I want the latency to be sorted as accurately as possible, and because I plan to re-amp as much as I can.

I haven’t tried an unbalanced re-record on the new card yet...
 
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