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Split Input Monitoring and Impedence
Old 19th March 2017
  #1
Gear Head
 

Thread Starter
Split Input Monitoring and Impedence

Hi,

I'm currently setting up a small home studio for songwriting and demos. I'd like to use split-input monitoring so I don't have to worry about any latency issues.

My initial plan was to split the output of my mic signal at my patchbay and send one ouput to my Scarlett interface for recording and another to my MG06X mixer for monitoring. I realise that phantom power is a problem with this setup so I've got an ART Phantom II Pro for that. What I'm not sure about is how this will affect impedence? Will this be a problem for the mic? Do I need a mic splitter - for example, a Whirlwind SP1X2? And what about for line-level sources?

Cheers!
Old 19th March 2017
  #2
Gear Maniac
 

Splitting at a patchbay will also halve the mic signal going to both inputs, to avoid that you need either a transformer, like used in budget passive mic splitters, or have an active device that uses a buffer.
Old 19th March 2017
  #4
Lives for gear
 

you could buy a splitter, but there is nothing wrong with using a y cable to split, it's done all the time. also the same method used in patch bays (multing)
Old 19th March 2017
  #5
Lives for gear
 

Quote:
Originally Posted by Unicornsfyeah View Post
Splitting at a patchbay will also halve the mic signal going to both inputs, to avoid that you need either a transformer, like used in budget passive mic splitters, or have an active device that uses a buffer.
I question this. My setup for ages has been a combo of preamps with dual or parallel line outs, or XLR y-splits, one side to the A/D the other to monitor/phones mixer. The whole point of the -what is it, 10/1? min impedance ratio for 'source to inputs is for the receiving input to allow minimal effect on the source. Add a transformer if dissimilar grounds isolation is need.
Old 19th March 2017
  #6
Gear Maniac
 

Quote:
Originally Posted by Wayne View Post
I question this. My setup for ages has been a combo of preamps with dual or parallel line outs, or XLR y-splits, one side to the A/D the other to monitor/phones mixer. The whole point of the -what is it, 10/1? min impedance ratio for 'source to inputs is for the receiving input to allow minimal effect on the source. Add a transformer if dissimilar grounds isolation is need.
If you split the mic signal before preamplification it's an issue, preamps with multiple out options will be buffered and splitting a line level, many mixers or preamps have enough gain to make up the difference.
Old 19th March 2017
  #7
Lives for gear
 

Hmm. He did say 'mic, rather than pre' out. But it's still not uncommon correct? One to main one to monitor mix?
Old 19th March 2017
  #8
Gear Maniac
 

Quote:
Originally Posted by Wayne View Post
Hmm. He did say 'mic, rather than pre' out. But it's still not uncommon correct? One to main one to monitor mix?
Well he mentioned having a phantom power supply to power the mics so it seems he wants to split the mic signal.
Old 19th March 2017
  #9
Gear Head
 

Thread Starter
Just to clarify, I'm splitting the signal after the 48V supply (ART Phantom II Pro) but before the mic pre.
Old 20th March 2017
  #10
Lives for gear
 

Quote:
Originally Posted by cpsmusic View Post
I'd like to use split-input monitoring so I don't have to worry about any latency issues.
Scarletts have direct monitoring dont they?
Old 20th March 2017
  #11
Gear Maniac
 

Quote:
Originally Posted by Lumbergh View Post
Scarletts have direct monitoring dont they?
I used to do this type of thing so I could add eq, comp and verb to my headphones with no latency too.
Old 20th March 2017
  #12
Gear Maniac
 

Quote:
Originally Posted by cpsmusic View Post
Just to clarify, I'm splitting the signal after the 48V supply (ART Phantom II Pro) but before the mic pre.
You need an active splitter or a passive transformer based mic split box. If memory serves me well, the passive ones can be had for ~$40 new per mic.
Old 20th March 2017
  #13
Gear Head
 

Thread Starter
Quote:
Originally Posted by Lumbergh View Post
Scarletts have direct monitoring dont they?
Yes, but I also want to add "comfort" effects for the performer via the mixer that's used for monitoring. My understanding (could be wrong) is that direct monitoring only works with the headphone output on the Scarlett.
Old 20th March 2017
  #14
Lives for gear
 

If thats the case (I RTFM years ago) use the HP out for monitoring, send it to whatever you want. You are recording, dont put anything you dont need to between the mic and the converters.
Old 20th March 2017
  #15
Gear Head
 

Thread Starter
Quote:
Originally Posted by Lumbergh View Post
If thats the case (I RTFM years ago) use the HP out for monitoring, send it to whatever you want. You are recording, dont put anything you dont need to between the mic and the converters.
So is it ok to send the Scarlett's headphone output to the mic/line input of the monitoring mixer?
Old 20th March 2017
  #16
Gear Maniac
 

Quote:
Originally Posted by cpsmusic View Post
So is it ok to send the Scarlett's headphone output to the mic/line input of the monitoring mixer?
It won't hurt anything and you'll get a signal, may not be ideal electronically but it will work.
Old 20th March 2017
  #17
Gear Maniac
 

I'm not sure how the routing works on those exactly though, if you can route direct monitor to just the headphones and playback to the main outs, you'd be able add effects to just the mic signal. If both set of outputs get the same signal, you'll need to split before the input still.
Old 20th March 2017
  #18
Gear Head
 

Thread Starter
Quote:
Originally Posted by Unicornsfyeah View Post
It won't hurt anything and you'll get a signal, may not be ideal electronically but it will work.
I realise it's unlikely to damage anything, but I'd like to set this up properly so I'm not sure I like the idea of a headphone output going to a mixer input.
Old 20th March 2017
  #19
Gear Maniac
 

Quote:
Originally Posted by cpsmusic View Post
I realise it's unlikely to damage anything, but I'd like to set this up properly so I'm not sure I like the idea of a headphone output going to a mixer input.
It won't produce an accurate eq response because of the signal mismatch. Splitting before the input would give much more accurate sound.
Old 20th March 2017
  #20
Lives for gear
 

Why are you trying to split the signal before the interface?

There is no difference in latency between the headphones or the main outs, the headphones get the signal from the main out, so there cant be any additional latency.

What you want is an external headphone amp you can place in series with your monitors (most have built in splitter/switching circuitry that mutes your monitors when using headphones. You can place any effects you need before the headphone amp. Most effects have a mix control and bypass. You can mix as much effect you need without a separate mixer and just bypass it when its not in use, or you can buy a switching box if you want to bypass both the effects and headphone amp when you want to use only the monitors.

The only reason you'd get latency is if you have the interface set for Processed monitoring instead of Direct monitoring. Both the headphones and Monitor sends should be the same. There's absolutely no reason to split anything up front and in fact its a dumb way of doing it because you wont hear the rest of the tracks playing in a multitrack situation.


If you're wanting to add effect to allow the listener to
Old 20th March 2017
  #21
Gear Maniac
 

Hang on now, it's actually a great idea on a budget and I used to do it.

You take the main outs of your interface into a stereo line input of your monitor mixer and your split input signals into a mono mic or line input, depending on where you split the signal. Then you can process the mic signal for just your headphone mix however you want or have gear for, with no latency whatsoever.
Old 20th March 2017
  #22
Lives for gear
Both devices have mic inputs with 3 kΩ impedance. Most mics can easily drive 1 kΩ, some even less, so it shouldn't be a problem.
Many modern mics have a quite low output impedance, so you won't get much loss, some mics have a bit higher impedance, but usually still less than 300 Ω, so you usually won't get a significant loss.
If both devices are at the same potential, you shouldn't need a transformer isolated splitter. Keep in mind that most transformer isolated (passive) splitters use transformers with 1:1 or 1:1:1 ratio that won't help with impedance matching and will even add some additional loss (and load) by themselves.
You shouldn't even need a separate supply for phantom powering. Simply engage the phantom power on only one preamp. The other preamp can handle it as it's inputs are already AC coupled so that it can cope with it's own phantom power when in use.
Old 20th March 2017
  #23
Gear Maniac
 

I remember a customer of mine needing a splitter snake for live use and we ended ordering one that was hundreds of dollars more so it would have transformer isolated outs.

It may work without but going into entry level preamps even 3-6db can end up meaning a noticble increase in the noise floor depending on how much you need to turn up the gain for your purpose.
Old 20th March 2017
  #24
Gear Head
 

Thread Starter
Quote:
Originally Posted by wrgkmc View Post
Why are you trying to split the signal before the interface?

There is no difference in latency between the headphones or the main outs, the headphones get the signal from the main out, so there cant be any additional latency.

What you want is an external headphone amp you can place in series with your monitors (most have built in splitter/switching circuitry that mutes your monitors when using headphones. You can place any effects you need before the headphone amp. Most effects have a mix control and bypass. You can mix as much effect you need without a separate mixer and just bypass it when its not in use, or you can buy a switching box if you want to bypass both the effects and headphone amp when you want to use only the monitors.

The only reason you'd get latency is if you have the interface set for Processed monitoring instead of Direct monitoring. Both the headphones and Monitor sends should be the same. There's absolutely no reason to split anything up front and in fact its a dumb way of doing it because you wont hear the rest of the tracks playing in a multitrack situation.


If you're wanting to add effect to allow the listener to
There are a couple of reasons why I wanted to do this. The main one is because I want to add "comfort effects" for the headphone mix. Obviously, I don't want to add these effects to the backing. With the setup you've described, how do you apply the effects only to the input signal and not to the backing track?
Old 20th March 2017
  #25
Gear Head
 

Thread Starter
Quote:
Originally Posted by Unicornsfyeah View Post
Hang on now, it's actually a great idea on a budget and I used to do it.

You take the main outs of your interface into a stereo line input of your monitor mixer and your split input signals into a mono mic or line input, depending on where you split the signal. Then you can process the mic signal for just your headphone mix however you want or have gear for, with no latency whatsoever.
Exactly!
Old 21st March 2017
  #26
Lives for gear
Quote:
Originally Posted by Unicornsfyeah View Post
I remember a customer of mine needing a splitter snake for live use and we ended ordering one that was hundreds of dollars more so it would have transformer isolated outs.

It may work without but going into entry level preamps even 3-6db can end up meaning a noticble increase in the noise floor depending on how much you need to turn up the gain for your purpose.
As I've already explained in my previous post, mic splitters use 1:1 transformers which give NO ADVANTAGE regarding the noise floor when compared to a simple Y split.
Radial, Sowter, Jensen, ART ... pretty much every transformer isolated passive splitter I know of is designed like that.
The purpose of transformers in a splitter is galvanic isolation.

If you were working with a 600 Ohm system (which is not the case), you'd loose a bit more than 3 dB when adding a second load.

In this situation we have two 3 kOhm inputs.
If you connect an SM58 with a source impedance of 150 Ohm, the difference is going to be 0.4 dB.
If you connect a TLM170 which has a source impedance of 50 Ohms, the difference is going to be 0.14 dB.
Old 21st March 2017
  #27
Gear Maniac
 

Quote:
Originally Posted by jetam View Post
As I've already explained in my previous post, mic splitters use 1:1 transformers which give NO ADVANTAGE regarding the noise floor when compared to a simple Y split.
Radial, Sowter, Jensen, ART ... pretty much every transformer isolated passive splitter I know of is designed like that.
The purpose of transformers in a splitter is galvanic isolation.

If you were working with a 600 Ohm system (which is not the case), you'd loose a bit more than 3 dB when adding a second load.

In this situation we have two 3 kOhm inputs.
If you connect an SM58 with a source impedance of 150 Ohm, the difference is going to be 0.4 dB.
If you connect a TLM170 which has a source impedance of 50 Ohms, the difference is going to be 0.14 dB.
Ok, I'll take your word for it then, you obviously have more electronic engineering chops than I. It's just in my experience it's usually a poor move to passively split signals especially instrument ones and headphones, when I had a setup like what the op wants I was using ISA One preamps and on those you can use the effects send as second output so I never had to split my mic signal. Using a splitter cable could save you ~$20-$30 vs a box so if it works, great.
Old 21st March 2017
  #28
Lives for gear
Quote:
Originally Posted by Unicornsfyeah View Post
Ok, I'll take your word for it then, you obviously have more electronic engineering chops than I. It's just in my experience it's usually a poor move to passively split signals especially instrument ones and headphones, when I had a setup like what the op wants I was using ISA One preamps and on those you can use the effects send as second output so I never had to split my mic signal. Using a splitter cable could save you ~$20-$30 vs a box so if it works, great.
That's because "instrument signals" usually have a high impedance source, so yes active splitting is usually the best option when dealing with el. guitars etc. With headphones... a good amp can drive several medium or high impedance headphones in parallel without a problem. The thing is that there are so many bad headphone amps and cheap headphones with really low impedance, that I could agree with you.

BTW if you use the insert send on the ISA One without plugging anything into the return, you're actually creating a passive (line level) split.
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