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Why are analog keyboards the poor cousins in audio interface connection?
Old 21st October 2013
  #1
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Why are analog keyboards the poor cousins in audio interface connection?

Hello all,

You want to record music digitally, so you're looking for an audio interface. Question one: what kinds of sources do you want to record, so what kinds of inputs do you need? And does your AI provide the facilities built right in to handle those inputs?

Microphones for voice and acoustic instruments - check - pretty much every modern AI has at least one input especially for microphones, in XLR format, with the special phantom power requirement taken care of, often switchable, and a pre-amplifier built right in to accomodate a mic's special level.

Guitars - check - pretty much all AIs are set up to directly input a guitar, with pre-amps adapted to their special input level.

External Digital Sources - check - pretty easy to find units with spdif and/or adat inputs of varying physical formats like rca, coax or toslink

Midi - check - very common to have Midi in/out capability built in.

External Analog Line-Level Sources, like effects boxes - check - usually either a combo xlr/slr jack or dedicated SLRs, with the internals to take direct line-level inputs from other boxes.

Analog Keyboards ...............uh, well, no, or at best maybe. Yes, there are barbarians who connect their mains-powered keyboards directly into line-level SLR inputs. But (a) keyboards don't actually output real line level, so you're left with a second-best mismatch; and (b) many pros strongly suggest not doing this anyway becaue of issues like hum and safety. No - to do this right, the analog keyboard player should pass through a Direct Injection (DI) box - which is essentially a transformer (if the passive type, recommended for keyboards). There'll be no pure input to the AI for the keyboard. The keyboard must first be colored by an external transformer and stepped down to mic level, only to be re-stepped up to line level by the AIs internal preamps. Down, up, down up.....Everyone else has their special input levels and format needs taken care of right in the AI - all but the lowly keyboard.

Why is this? Is it that analog keyboards and other similar sources are so uncommon anymore that it's not worth building inputs for them into AIs?
Old 21st October 2013
  #2
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filipv's Avatar
I really don't see a problem with connecting synths to the line-in ports. To my ears, there is no recognizable degradation in sound. One just needs to be careful with the output level from the synth, use decent cables and connectors... and that's about it.
Old 21st October 2013
  #3
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UnDeFiNeD's Avatar
 

Quote:
Originally Posted by filipv View Post
I really don't see a problem with connecting synths to the line-in ports. To my ears, there is no recognizable degradation in sound. One just needs to be careful with the output level from the synth, use decent cables and connectors... and that's about it.
There is a real problem in doing so as the OP correctly stated.
It is an unbalanced signal coming from a keyboard, and those may never be connected to a balanced input without the correct cabling.
If you connect those two using regular unbalanced cable, you will have sound, but the keyboards chassis ground will be connected to the audio ground of the interface, so unless you are lucky you can expect lots of interference and ground loop problems.

To as why keyboards don't have the pro connections, one can only guess that since it's an instrument, unbalanced consumer connections are preferred over professionally balanced cabling since an ordinary musician isn't expected to have a studio and the interfacing that goes with it.

It's made to be plugged into an amp.

Alex

Sent from my GT-N7100
Old 21st October 2013
  #4
There's NO safety issue though...don't know where that point came from!

And what's wrong with the inbuilt di in the interface?
Old 21st October 2013
  #5
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Quote:
Originally Posted by psycho_monkey View Post
There's NO safety issue though...don't know where that point came from!
I'm fascinated to know where that came from :p
Old 21st October 2013
  #6
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I'm sure that came from people who advise to cut the mains earth connection on devices when there are ground loop problems, which IS a really hazardous operation.

Improperly connecting unbalanced with balanced is not dangerous of course, just uneducated.

Alex
Old 21st October 2013
  #7
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filipv's Avatar
Quote:
Originally Posted by UnDeFiNeD View Post
It is an unbalanced signal coming from a keyboard, and those may never be connected to a balanced input without the correct cabling.
well, I assumed that the cabling IS correct. Use "stereo" plugs with wires on the tip and the "ground", leave the middle alone, and that's about it.

Much cheaper than DI.
Old 21st October 2013
  #8
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What's an SLR?
Old 21st October 2013
  #9
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Quote:
Originally Posted by rcb4t2 View Post
What's an SLR?
I think he meant to type XLR, unless I'm mistaken . . .
Old 21st October 2013
  #10
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I figured, but this threw me off...

Quote:
Originally Posted by musicus View Post
usually either a combo xlr/slr jack or dedicated SLRs, with the internals to take direct line-level inputs from other boxes.
Anyway I usually treat keyboard outputs the same as guitar/bass - DI to mic pre. Sometimes I use a step up balancing box (ebtech LLS) and just run them as line level.
Old 21st October 2013
  #11
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O.F.F.'s Avatar
 

Quote:
Originally Posted by rcb4t2 View Post
What's an SLR?
Single Lens Reflex camera

Self-Loading Rifle

Satellite Laser Ranging

Scaleable Linear Recording

Semi-Linear Resolution

Simple Linear Regression

Sending Loudness Rating

Systematic Literature Review

Statutory Liquidity Ratio

Sri Lankan Rupee


That's all wiki came up with.
Old 21st October 2013
  #12
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UnDeFiNeD's Avatar
 

Quote:
Originally Posted by filipv View Post
well, I assumed that the cabling IS correct. Use "stereo" plugs with wires on the tip and the "ground", leave the middle alone, and that's about it.

Much cheaper than DI.
Unfortunately, thats exactly the wrong type of connection most folks unknowingly make.
And very understandably so, since we see a jack output and a jack input and furthermore we hear sound when we connect both!

But this type of connection can contaminate your whole audio system by introducing hum and interference (try putting your cellphone near a metal case synth in that type of connection, and try that again using for instance a DI between both).

If the extra gain a mic input could offer you isn't necessary (eg. if the output is hot enough), and you want to avoid the extra cost/complexity of a DI then do the following:

- Use a TS jack on the synths output, and a TRS on the line input.
- Connect the synth's output "Tip" to the Line inputs "Tip"
- Connect the synth's output "Sleeve" to the Line inputs "Ring"
- Only connect the Cable's shield to the line input's "Sleeve", but DO NOT CONNECT IT on the side of the synth


This is the only way to connect unbalanced gear with balanced gear and avoid contamination.

Alex
Old 21st October 2013
  #13
I've been plugging the line out of my outboard synths into line ins on my various rigs for well over 20 years and have never had noticeable signal degradation or noise (vis a vis headphone out or, in the case of one synth that had a digital ADAT lightpipe output, going straight over digitally).

Mains-ground safety problems are a serious issue, but with properly set up studios, it's hard for me to imagine a problem arising plugging an undamaged synth into a properly set up and functioning interface, mixer, etc.
Old 22nd October 2013
  #14
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Quote:
Originally Posted by rcb4t2 View Post
What's an SLR?
It's a TRS jack when you're typing a post over breakfast, not yet quite awake.
Old 22nd October 2013
  #15
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andychamp's Avatar
If the keyboard's output level is somewhere between line and instrument level, I'd use the gtr. input and turn the synth's master volume to below clipping point, no big deal...
Old 22nd October 2013
  #16
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Quote:
Originally Posted by theblue1 View Post
I've been plugging the line out of my outboard synths into line ins on my various rigs for well over 20 years and have never had noticeable signal degradation or noise...
Quote:
Originally Posted by filipv View Post
I really don't see a problem with connecting synths to the line-in ports. To my ears, there is no recognizable degradation in sound. One just needs to be careful with the output level from the synth, use decent cables and connectors... and that's about it.
Quote:
Originally Posted by UnDeFiNeD View Post
There is a real problem in doing so as the OP correctly stated.
From reading online, I gather there is a great deal of conflicting information and opinions on this general subject. Consider this article, that appears to me to be well written:

Q. Is there any point in DI-ing keyboards?

"...In the majority of cases, electric and electronic keyboards provide an unbalanced output at a level typically 10-20 dB below standard line level."

"...A DI box inherently contains a transformer and can be used to provide galvanic isolation, preventing ground-loop issues. It also gives complete protection from phantom power....Phantom power can, and occasionally does, destroy the output stages of keyboards ..."

"...Running a keyboard via a DI box has a number of other useful benefits. For example, some very early electronic and electric keyboards do work better into the very high input impedances (ie. well over 100k?) that a DI box provides, rather than the 10k? or so impedance of a standard line-level input...."


And consider the Focusrite Scarlett 18i20 user manual:

http://d3se566zfvnmhf.cloudfront.net...guide-en_0.pdf

Page 14, Recording a Band - shows the analog keyboard connected through a DI box, and the text confirms "A selection of sources – microphones, a guitar and DI boxes – are shown connected to the Scarlett 18i20’s inputs.

So UnDeFiNeD & rcb4t2 seem to be on the connection puritan's path:

Quote:
Originally Posted by UnDeFiNeD View Post
...If you connect those two using regular unbalanced cable, you will have sound, but the keyboards chassis ground will be connected to the audio ground of the interface, so unless you are lucky you can expect lots of interference and ground loop problems.
Quote:
Originally Posted by rcb4t2 View Post
... I usually treat keyboard outputs the same as guitar/bass - DI to mic pre. ...
My point, however, is not so mcuh to have a debate on the necessity of DIs for keyboards, but rather why should a DI be necessary at all for them?

Audio interfaces are designed with the necessary connection facilities built right into them for most other common sources. Built-in XLR connectors, pre-amps and phantom power for microphones; TRS jacks with padding and impedance matching for guitars, line-level inputs for line-level devices, and spdif/adat inputs for digital devices.

But if an audio interface exists that has the desirable connectivity features of a DI box built into it for keyboard input, it is so rare and so unkonwn that I haven't found it. Only the keyboard is left to fend for itself on connectivity ,as if it was so unimportant as to not warrant attention.

Audio interface manufacturers go on and on about the qualty of their pre-amps as if you would not want to trust the conditioning of your input to any other device - but then leave keyboards to pass through someone else's transformer just to connect to their pre-amps.

And my question is from a bad stand-up routine: What's up with that? As a keyboardist, this seems like a glaring functional omission. But maybe I have an inflated opinion of the importance of analog synths and other keyboards. Maybe they're really not that common or important in the big scheme of modern music making.
Old 22nd October 2013
  #17
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OK, so here's where I get really confused.

The Scarlett 2i2 web page:

Scarlett 2i2 | Focusrite

says :

"Plug straight in - The front panel high quality combination input can be used to connect line and instrument level signals as well as microphones. This makes it perfect for recording the output of a synthesizer or stage piano, whilst at the flick of a switch you can cater for the output of an electric or acoustic guitar."

(Note - I really don't mean to single out Focusrite - on the contrary I really really like their equipment from the ton of reading I've done on them and have pretty much decided it's one of theirs I'll be buying next - but that just means that's the documentation I'm most familiar with to use as an example.)

But the user manual specifies:

"Set the LINE/INST switch next to the socket to INST if you are connecting a musical instrument (a guitar in the example) via an ordinary 2-pole (TS) guitar jack, or to LINE if you are connecting a line level source such as the balanced output of a stage piano via a 3-pole (TRS) jack. Note the Combo connector accepts both TRS and TS types of jack plug."

So, ok - mic, or guitar, or a keyboard that has a balanced output at line-level. Much better than most others for sure. But if your keyboard - like most I know - doesn't have a balanced output at line level? And most AIs don't even have the 2i2's facility for keyboard input.
Old 22nd October 2013
  #18
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UnDeFiNeD's Avatar
 

Hi Musicus,

I agree with your point that (classic) synth interfacing in a home studio context is not well documented, and maybe even under represented.

The average line of AI's tries to cater to as wide an audience as possible of course.
Thats why the average interface in that price class has a couple of combo Mic/Line/DI inputs (usually two) to allow you to connect two mics OR two guitars OR a stereo synth (assuming unbalanced outputs).
The rest of the inputs on those types of interfaces feature balanced line level inputs, which are a lot cheaper/less consuming/space saving to built, so the manufacturer assumes that you take care of any sort of preamp(+ DI) if connecting something other than a balanced line level device. Same goes for any additional digital input.

With the sudden surge of very affordable (analog) synths, I think the market is missing a cost effective (multichannel) synth preamp to allow anyone to use those extra line in's to connect these synths without getting into trouble with interference.

However, if your synths signal is high enough (if not, try if you have a -10dBV option on your line input instead of +4dBu, you'll win some 12dB's of gain!), and output impedance low enough (<1k ohms just to be sure), you can use those balanced line in's on your interface, but do so using the cable connection which I showed in my previous post (here)

Alex
Old 22nd October 2013
  #19
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Quote:
Originally Posted by UnDeFiNeD View Post
...The average line of AI's tries to cater to as wide an audience as possible of course. Thats why the average interface in that price class has a couple of combo Mic/Line/DI inputs (usually two) to allow you to connect two mics OR two guitars OR a stereo synth (assuming unbalanced outputs). ...
Agreed, and thanks for the feedback.

But these "DI inputs" - if I've understood right from what I've read, these are optimized for guitar input. They have higher gain than mic and lower than line to accomodate guitar-level input, are designed to accept unbalanced input, and hi-Z for impedance matching - but (a) keyboard output level is different again; an (b) no galvanic isolation (since it's not a concern for guitars), at least that I can find mentioned. So while you can, sort of, connect an unbalanced, non-line-level keyboard (which is most keyboards) to them, it's not actually recomended or intended for that.

But I would love to discover I've misunderstood!

And, just to be clear - this isn't about keyboardists feeling unloved. You shop for a great AI that has quality circuitry so it will reproduce your instrument's input with crystal clear, unadulterated fidelity - only to discover that you can't actually, properly, connect your instrument directly to that AI. You have to go through a DI, and feed your crystal clear AI a signal that's been dirtied up by joe-blow's DI transformer. So what was the point of the crystal clear AI? You can, sort of, work around it - but you'd think there'd be some AI out there with at least one input that's actually designed for normal keyboard input.
Old 22nd October 2013
  #20
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Quote:
(b) no galvanic isolation (since it's not a concern for guitars)
Are you sure you're not looking to an audio interface to solve the wrong problems, here? I don't understand why you have this concern (for keyboards but not mics/guitars).
Old 22nd October 2013
  #21
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UnDeFiNeD's Avatar
 

Quote:
Originally Posted by musicus View Post
Agreed, and thanks for the feedback.

But these "DI inputs" - if I've understood right from what I've read, these are optimized for guitar input. They have higher gain than mic and lower than line to accomodate guitar-level input, are designed to accept unbalanced input, and hi-Z for impedance matching - but (a) keyboard output level is different again; an (b) no galvanic isolation (since it's not a concern for guitars), at least that I can find mentioned. So while you can, sort of, connect an unbalanced, non-line-level keyboard (which is most keyboards) to them, it's not actually recomended or intended for that.

But I would love to discover I've misunderstood!

And, just to be clear - this isn't about keyboardists feeling unloved. You shop for a great AI that has quality circuitry so it will reproduce your instrument's input with crystal clear, unadulterated fidelity - only to discover that you can't actually, properly, connect your instrument directly to that AI. You have to go through a DI, and feed your crystal clear AI a signal that's been dirtied up by joe-blow's DI transformer. So what was the point of the crystal clear AI? You can, sort of, work around it - but you'd think there'd be some AI out there with at least one input that's actually designed for normal keyboard input.
Di's inputs (eg. hi-Z instrument inputs) are in fact optimised for synth use.

Impedance:

I have seen you use that word "impedance matching" a couple of times now, but matching is not what is used in pro-audio.
Impedance matching optimises the power (in Watt's) transfer between two devices.
But in studio audio (and live, etc.) we need to optimise the voltage transfer between devices.
This is done using "impedance bridging"

Without going into the maths of calculating so, input impedance (Z in) needs to be a lot bigger than output impedance (Z out) (about 10x works ok in most cases) to match voltages.
That's what Hi-Z means, having a huge input impedance.

Since keys have a lower output impedance than guitars (keys can deliver a lot more current!), there isn't a problem and voltage will be properly matched.

Galvanic isolation:

Simply put, not needed at all. Galvanic isolation is a nice plus when having a passive DI (eg. transformer) on the input to avoid potential problems.
But what is needed is to avoid throwing the keyboards chassis ground together with the balanced systems audio ground.
That, again is done by using proper cabling to connect both, and not by using galvanic isolation.



Gain/Level:

While it's true that it does not need the amount of gain a guitar requires, it's good to have some 10 to 20dB's of gain to make synths line level.
If at all the signal is too hot, a -20dB pad option is usually available.


Alex
Old 22nd October 2013
  #22
Registered User
Somewhere in between the Mic, Instrument, -10dbV and +4dbU line level inputs - I think most audio interfaces have synth output levels well covered. I'm just not seeing the problem.

However - the limitations of unbalanced cables are a problem. Less so than with guitars, which are truly the poor nephew of audio engineering. (Except for the very few rare balanced pup guitars which are more like the real original that Les Paul invented).

So there can be a problem with ground loop hum, and that is where some transformer isolation works brilliantly. And I've never thought transformers to be a problem with analog gear - imo the very best analog gear is full of transformers. People are too cheap to use them these days, but that's where a collection of passive DI's, Reamp boxes, Hum Eliminators, Line Level Shifters etc is extremely useful.

If we were talking about connecting a synth to an API or Neve preamp nobody would be whining about it ... get some transformer love into your analog sound.
Old 22nd October 2013
  #23
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The thing with transformers is that good ones sound sublime but cost the earth while cheap ones are atrocious.

They are fine if we are talking SSL/Neve level consoles but once you go down the price scale they can quickly become a liability to overall SQ.
Old 22nd October 2013
  #24
i use a ground lift DI on synths that don't respond well to running direct.
would be nice if more preamp/converters included this feature along with phantom power & invert phase.
Old 23rd October 2013
  #25
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Quote:
Originally Posted by musicus View Post
OK, so here's where I get really confused.

The Scarlett 2i2 web page:

Scarlett 2i2 | Focusrite

says :

"Plug straight in - The front panel high quality combination input can be used to connect line and instrument level signals as well as microphones. This makes it perfect for recording the output of a synthesizer or stage piano, whilst at the flick of a switch you can cater for the output of an electric or acoustic guitar."

(Note - I really don't mean to single out Focusrite - on the contrary I really really like their equipment from the ton of reading I've done on them and have pretty much decided it's one of theirs I'll be buying next - but that just means that's the documentation I'm most familiar with to use as an example.)

But the user manual specifies:

"Set the LINE/INST switch next to the socket to INST if you are connecting a musical instrument (a guitar in the example) via an ordinary 2-pole (TS) guitar jack, or to LINE if you are connecting a line level source such as the balanced output of a stage piano via a 3-pole (TRS) jack. Note the Combo connector accepts both TRS and TS types of jack plug."

So, ok - mic, or guitar, or a keyboard that has a balanced output at line-level. Much better than most others for sure. But if your keyboard - like most I know - doesn't have a balanced output at line level? And most AIs don't even have the 2i2's facility for keyboard input.
Some keyboards do have line-level balanced outputs. I would agree that most don't. If it does, then run it into a line input.

An interface's DI is mostly the same as a standalone DI box. You can use it equally easily for a guitar or unbalanced synth output. Or a bass, or accordion pickup, or violin pickup... or anything that fits under the wide umbrella of "unbalanced instrument level". The primary difference is that a interface's DI usually isn't transformer isolated. The input will likely just handle balancing, impedance, then pass the signal along to the mic preamp on the channel in question.

If you have a ground loop problem from the synth (or from a guitar split to an amp, or x, y, z, etc), usually a tx-equipped DI will help. Not always. Same issue with DI guitars though, if they're connected to something else that's active (certain pedals, amps, etc).

I think you're overthinking this one. If the synth has a balanced line level output, (virus, for example are like this) run it into the line input. Else use a DI, external or built-in. Unlike passive guitar pickups, picky impedance considerations probably don't apply. In many ways, a keyboard is easier to get in direct.
Old 23rd October 2013
  #26
Quote:
Originally Posted by UnDeFiNeD View Post
I'm sure that came from people who advise to cut the mains earth connection on devices when there are ground loop problems, which IS a really hazardous operation.

Improperly connecting unbalanced with balanced is not dangerous of course, just uneducated.

Alex
you can't fix stupid though!
Old 23rd October 2013
  #27
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Quote:
Originally Posted by UnDeFiNeD View Post
There is a real problem in doing so as the OP correctly stated.
It is an unbalanced signal coming from a keyboard, and those may never be connected to a balanced input without the correct cabling.
If you connect those two using regular unbalanced cable, you will have sound, but the keyboards chassis ground will be connected to the audio ground of the interface, so unless you are lucky you can expect lots of interference and ground loop problems.

To as why keyboards don't have the pro connections, one can only guess that since it's an instrument, unbalanced consumer connections are preferred over professionally balanced cabling since an ordinary musician isn't expected to have a studio and the interfacing that goes with it.

It's made to be plugged into an amp.


Alex

Sent from my GT-N7100
Nonsense.
Old 23rd October 2013
  #28
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UnDeFiNeD's Avatar
 

Quote:
Originally Posted by cavern View Post
Nonsense.
Thanks for that enlightened remark.
Care to elaborate?

Alex


Sent from my GT-N7100
Old 23rd October 2013
  #29
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Quote:
Originally Posted by UnDeFiNeD View Post
Thanks for that enlightened remark.
Care to elaborate?

Alex


Sent from my GT-N7100
Sure professor,i've recorded keyboards of many kinds into several interfaces,old and new for many years.I do it now.It sounds just fine.No noise with proper gain staging.
I couldn't have gotten lucky every time.
Interfaces i've done this with:
Aadvark Q-10
1200F
Zed R16
UFX
MR816

I try not to spend all day gathering technical data,i prefer to make music.
Old 24th October 2013
  #30
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For the types of audio interfaces being mentioned, I suggest going thru the mic pre. You need cables that have a quarter inch TS on one end and an XLR on the other. Tip goes to pin 2. Sleeve goes to pins 1 and 3 which are tied together.

How to wire an XLR

I run a larged synth rig which I have wired to an Audient Zen, which then feeds a Lynx Aurora. Vintage King provided the mogami cable wired as mentioned above (which was suggested by Audient). Going into mic pre of a mixer should be similar to going into mic pre of an audio interface.

This system works well and is clean.

Tom
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