Connection/gain staging question

[Delaware Dave]

Need some help with these scenarios:

 

1) two inputs going into a mixer, both inputs are TS, one is a TS plug coming from the Vent going into channel 1 of the mixer and the other is a TS plug coming from my keyboard"s output that only accepts TS and is going into channel 2 of the mixer. What is the recommended plug going from the mixer out to the powered monitor, a TS plug or a TRS plug? The mixer's output and powered monitor input can accept either.

 

2) two inputs going into a mixer, both inputs are TRS plugs coming from two keyboard whose connections accept TRS. What is the recommended plug going from the mixer out to the powered monitor, a TS plug or a TRS plug?

 

3) two inputs going into a mixer, one is TS coming from the Vent and the other is a TRS coming from my keyboard. What is the recommended plug going from the mixer out to the powered monitor, a TS plug or a TRS plug?

 

I'm trying to understand this from a gain staging perspective.

 

[Markyboard]

Assuming your mixer output and monitor input is balanced differential you"re better off using TRS in all 3 cases. This will give you both sides of the differential amp signal coming from your mixer which is what the monitor/amp input is optimally designed to receive. Although the mixer input and output stages are basically independent for optimal gain staging you want to achieve as close to the nominal input level at your mixer input stage and same for your monitor amp input.

 

Hope that makes sense.

[PianoMan51]

There is no relationship between TR and TRS wrt inputs and outputs. Balanced (TRS) and unbalanced (TR) are two different ways to transmit an electrical signal, but the signal itself remains the same.

 

For gain staging the difference is 6dB. TRS delivers a 6dB hotter signal than TR. So, for example, if you have a keyboard output jack that supports both TR and TRS, and an input jack on your mixer or amp that also supports both, then a TRS cable will deliver 6dB more power (4x) than a TR cable.

 

Most of the time this is inconsequential because your mixer has plenty of gain on the input (usually the first adjustment in a channel strip named 'gain') and the output (the output volume slider).

 

There are times when (wrt to gain staging) you might want that extra 6dB. This is when the output device has output levels normalized at -10dB but your amp is normalized at +4dB. Due to a difference in the definition of '0dB' the real world difference is 12dB. In these cases using a TRS cable will add 6dB to make up the 12dB loss.

[Delaware Dave]

There is no relationship between TR and TRS wrt inputs and outputs. Balanced (TRS) and unbalanced (TR) are two different ways to transmit an electrical signal, but the signal itself remains the same.

 

For gain staging the difference is 6dB. TRS delivers a 6dB hotter signal than TR. So, for example, if you have a keyboard output jack that supports both TR and TRS, and an input jack on your mixer or amp that also supports both, then a TRS cable will deliver 6dB more power (4x) than a TR cable.

 

Most of the time this is inconsequential because your mixer has plenty of gain on the input (usually the first adjustment in a channel strip named 'gain') and the output (the output volume slider).

 

There are times when (wrt to gain staging) you might want that extra 6dB. This is when the output device has output levels normalized at -10dB but your amp is normalized at +4dB. Due to a difference in the definition of '0dB' the real world difference is 12dB. In these cases using a TRS cable will add 6dB to make up the 12dB loss.

Let's now assume for #3 above that the mixer is out of the equation since your answer indicated that the mixer at the channel level would balance out the signals by adjusting of the gain on the channel strip, so I would have a -10 db going directly from the device into input 1 of the monitor and a +4db from the other device going directly into input 2 of the monitor. I would assume that the input 2 signal would be louder because it is carrying a +4db signal whereas input 1 is receiving a -10db? You also mentioned a 12 db real world difference. Mathematically -10 to +4 is a 14 db difference. How do you calculate only12db's?

[PianoMan51]

Sidebar: the difference between dBv and dBu. These have slightly different zero points. 14 becomes 12. Google is your friend.

 

It might be helpful to know what the specs on your 'monitor' are. If there are multiple inputs or volume knobs, then your monitor has a little mixer built in.

 

Next, what are your source specs? This includes the levels of your keyboard and vent outputs.

 

I"m not pulling your chain at all. In the end, setting up good gain staging starts with the specs.

 

Come back and we can work this through!

 

 

[Delaware Dave]

Pianoman, i'm not necessarily trying to troubleshoot, I'm more trying to understand so that I can make the proper setups not just on my personal situation but in general. I think I now have the understanding. Thanks.... Btw, i didnt distinguish dbu from dbv prior to today. Thanks for that.

[J. Dan]

Unless you're running long distance in a high noise environment, the advantage to balanced is likely negligible. It's a different story running from stage to FOH through a snake. But if you have a mixer and monitor sitting right next to you on stage, there will likely be no discernible difference.

 

Balanced TRS will only do anything at all if both the output AND input are TRS balanced at both ends. If not, even with a TRS cable, you're still running unbalanced.

 

As far as gainstaging, when it comes to electronic active devices (does not apply to mic preamps or other instruments like guitars), it's not a bad rule of thumb to keep your signal hot up front and in each stage as long as you have enough headroom without clipping going into the next stage.

[Dr Mike Metlay]

A couple of facts to spackle around the edges of the mostly excellent stuff presented above:

 

The difference between a balanced and an unbalanced signal is that the unbalanced signal has two conductors, one for the signal itself and one for a ground reference (which also carries signal, the Wikipedia page on balanced audio is a good read). When you're using a 1/4" plug, the tip is the hot signal and the sleeve is the ground, so these are nicknamed TS.

 

On the other hand, a balanced signal requires three conductors, one for the signal (hot), one for a dedicated ground that carries no signal, and one for the inverse of the signal (cold). XLR cables almost always run balanced signals, and the most common convention today (after decades of conflicts between manufacturers is pin 1 is ground, pin 2 hot, pin 3 cold, or "pin 2 hot" for short. In a 1/4" plug, you add a third conductor, the Ring, to carry the cold signal... this gives you TRS plugs.

 

The reason this is done is primarily for common-mode rejection. If an cable runs near a power supply, unshielded monitor, or other source of electromagnetic radiation, it picks up noise, which becomes part of the signal. In an unbalanced cable, that's the end of the story: the signal+noise gets to the next stage and it's part of your sound.

 

However, in a balanced cable, the same noise hits both wires and "infects" the hot and cold signals the same way: on the hot you have Signal + Noise and on the cold you have (âSignal) + Noise. When your signal gets to the balanced input stage, it flips the cold signal again and adds it to the hot:

 

(S + N) + (â(âS + N) = S + N + S + (âN) = S + S + N â N = 2S. (twice the signal is a 6 dB boost, as mentioned above)

 

The noise is the same on both wires, so when you invert the cold and add it to the hot, it effectively cancels itself out. This is one of the reasons why balanced cable runs can go for hundreds of feet while unbalanced cables get crufty over more than about 15 feet. (The other is impedance, a different topic entirely).

 

There are various ways that balanced input stages can be set up, trading expense for effectiveness. The most common are differentially balanced, where the above inversion and cancellation takes place, and impedance-balanced, where the hot signal's source impedance is balanced by a closely matched impedance between the cold and ground signals, resulting in the same effect. Impedance balancing is much cheaper than differential balancing, and is often quite effective.

 

As to whether or not there's any difference using a TS or TRS cable into here and out of there, I defer to Mike Rivers, who is hopefully reading this thread and has a plethora of knowledge about how this stuff works in practice.

 

Hope this helps,

 

mike

[Theo Verelst]

The argument that balanced is hotter and therefor gets a higher signal to noise ratio is very dependent on the circuit, and often simply isn't true. Balancing impedance can be an important part of the balanced connection for various kinds of disturbance prevention. Connecting to a proper input w.r.t. the output being high or low signal voltage and being somehow balanced or not can be important.

 

Hum and noise aren't the only consideration when connecting up instruments to mixer: keyboards probably don't benefit from a low impedance Mic input with the gain screwed down, specific line level inputs might be better adapted. Balanced all the way (actually balanced outputs, properly balanced cable (including capacitance) , and actually balanced input (either transformer or active electronics) has advantages, but also a disadvantages: inherent distortion, and audible artifacts from coupling capacitors imbalance.

 

T

[Markyboard]

The argument that balanced is hotter and therefor gets a higher signal to noise ratio is very dependent on the circuit, and often simply isn't true.

 

I was just about to post something similar after learning that my long held assumption was wrong. I always thought that balanced outputs provided twice the signal level but in fact they"re halving the nominal level though the hot and cold differential driver pair. An unbalanced driver doesn"t do this so all other things being equal a balanced signal should provides the same level as unbalanced.

 

Thanks Theo!

[Theo Verelst]

A little explanation. Balancing is mainly two possibilities in electronics, for two main reasons. Clearly balancing prevents hum and rattle in many cases, which for low signal level sources like microphones is usually a necessity (though certainly not always). Also, there's ground loop induced signal disturbance coming from differences in load patterns during the positive and negative going supply lines of for instance heavy amplifiers that cause ground currents, and those ground currents can flow through the music signal wires ground circuit, causing a distortion voltage. Normally speaking the balancing will in the lower frequency range work good, electronically or with a transformer. There is however the issue of the coupling capacitors, where it is not unlikely that each part of the balanced input pair and each part of the connected balanced output pair has a coupling capacitor in the signal path. For modern (relatively) low impedance connections, these are probably all four electrolytic capacitors of a significant capacitance. Unfortunately, these can act non-linear when becoming charged in inverse, and also, the tolerance of the actual capacitance w.r.t the specified one can be rather large (-20%+50% or something), so if the two capacitor chains of series coupled out and input capacitances are compared in agregated form, it is likely the actual capacitance in the non-inverting output-input connection is quit noticeably different from the the inverting pair. This is normally not of great consequence, the roll off frequency of this high pass filter is most likely under 20Hz and not problematic. However, the difference in coupling capacitance can easily create a huge imbalance for very low frequencies, which makes the circuit sound distorted in the face of ground currents.

 

Noise over the connection isn't easy to fully analyze, but if you consider the scenario of perfectly unbalancing and perfectly balancing signals electronically, adding an extra amplifier with the same signal amplitude doesn't necessarily lower the overall noise of the output buffers or input buffers, maybe the noise increase witl be 3dB compared to getting 6dB more out of the adder of the unbalanced components, but it isn't sure.

 

T