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clueless recording question regard XLR out from amp to interface

pcake

pcake

Sep 20, 2011
10,169
31,502
Los Angeleez
#1
both my combo (rumble 40) and my head (TC BQ250) have balanced XLR out. i'm getting a motu M2 - do i need an XLR to XLR cable, and will i then need to go through the mic input or can i use an XLR to 1/4 cable (they seem to be unbalanced) or an XLR to 1/4 adapter? or does it even matter?

i've been looking at manuals, but sadly after all these years, i only sort of understand balanced vs unbalanced, and have no clue what - if anything - it will mean for recording on the motu M2 interface. in the past, i've only used an XLR cable for mics, and in fact think of them as mic cables.

this is what the motu manual says:
Connect a microphone, guitar or line-level analog input to the XLR/quarter-inch combo jacks with either a standard mic cable or a balanced cable with a quarter-inch plug.

☛ Do not connect a +4 (line level) XLR cable to the inputs (because of the preamps). Use a quarter-inch input instead."
Click to expand...

they don't seem worried about it, so maybe i shouldn't be either.
 
#3
er... mic level? line level? when we previously recorded my singing and bass were the same volume, but i suspect that's not what you're talking about... or is it?

i have the power to turn my outgoing level down from my amp - at least, i do on the one with post and pre out. or i can turn down the gain on the motu.

to be frank, i just don't want to hurt the amps or the interface. other than that, i can experiment.
 
#4
Patti, from what I understand, mic level and line level refers to the impedance of each, not the volume. Mic level has a lower impedance than line level. Usually there's a switch or button on the mixer/input device that will switch from mic to line/instrument when it has a combined XLR 1/4" connector so that you can plug in either a mic or an instrument.
 
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#5
after looking this up, this is what i found. is it correct? hopefully...
Several different types of devices are used to boost microphone levels to line–level signals. Mixers are probably the most popular piece of equipment, since they can also combine multiple signals together into a single output. Preamplifiers and mic-to-line amplifiers also do the job just as well and are available as single-channel or multi-channel devices.

A line-level signal is about one volt, or about 1,000 times as strong as a mic-level signal. The two signal types do not ordinarily use the same input. This signal travels from your pre-amp to the amplifier.

Shure said there are two standard line levels: +4 dBu for professional equipment (mixing desks and signal processing gear) and -10 dBV for consumer equipment such as DVD and audio players.


The other two types of audio signals are instrument and speaker levels. Like mic-level signals, instrument-level signals (such as an electric guitar or bass) require preamplification to bring them up to line level. Post-amplification speaker-level signals are even higher in voltage than line level and require speaker cables for safe signal transfer.

It’s critical to match a device to the correct input, since there’s no technical tolerance for mistakes. Otherwise, it fails. For example, connecting a microphone to a line-level input will result in almost no sound at all since the mic-level signal is too weak to drive the line-level input.
Click to expand...
Invalid Link Removed
 
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#6
Mic, instrument, and line level refer to signal levels. Per the linked article mic level is about -30dBu, instrument level is about -20dBu, and line level is about +4dBu. Line level, instrument level, mic level explained

You could also could convert the dBu levels into voltage levels.

These are general terms as hot mic level crosses into instrument level, and hot instrument level crosses into line level.

Regarding balanced versus unbalanced. Instrument cables have two conductors. One of the conductor is grounded and the other carries the signal. Instrument cables are coaxial, so the ground is wrapped around outside of conductor that carries the signal. This called a shield and it is designed to help reduce induced noise.
Balanced-vs-Unbalanced-2.jpg



Mic cables have three conductors. Two conductors carry the signal and they do not have to be referenced to ground, so they essentially float. Because the two conductors are parallel they benefit from what is called common mode rejection. Essentially if a voltage is induced in one cable, the same voltage will be induced in the other cable so it cancels out because there is not voltage differential. The third conductor is the ground. A mic cable is coaxial like an instrument cable so the grounded shield is wrapped around the two conductors that carry the signal.

balanced-wiring.jpg


Images from What’s the Difference Between Balanced and Unbalanced?
 
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#7
Wasnex said:
Mic, instrument, and line level refer to signal levels. Per the linked article mic level is about -30dBu, instrument level is about -20dBu, and line level is about +4dBu. Line level, instrument level, mic level explained

You could also could convert the dBu levels into voltage levels.

These are general terms as hot mic level crosses into instrument level, and hot instrument level crosses into line level.

Regarding balanced versus unbalanced. Instrument cables have two conductors. One of the conductor is grounded and the other carries the signal. Instrument cables are coaxial, so the ground is wrapped around outside of conductor that carries the signal. This called a shield and it is designed to help reduce induced noise.
View attachment 3860337


Mic cables have three conductors. Two conductors carry the signal and they do not have to be referenced to ground, so they essentially float. Because the two conductors are parallel they benefit from what is called common mode rejection. Essentially if a voltage is induced in one cable, the same voltage will be induced in the other cable so it cancels out because there is not voltage differential. The third conductor is the ground. A mic cable is coaxial like an instrument cable so the grounded shield is wrapped around the two conductors that carry the signal.

View attachment 3860338

Images from What’s the Difference Between Balanced and Unbalanced?
Click to expand...

thank you - i need to read this a couple times and absorb it.

and probably upgrade our order to the M4, which has mic preamps on both front inputs and 2 inputs on the back that don't go through the preamps.
 
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#8
As far as impedance, I believe microphone and guitar cable are about the same impedance. I reviewed datasheets for Belden instrument and microphone cable, and the impedance was 40 ohms for both.

Often instruments are referred to as high impedance and microphones are referred to as low impedance. I believe this relates to the typical source impedance of instruments and mics, and also the typical input/load impedance of the circuits you use to amplify their signals. For example the input impedance on many instrument amps is 1 Meg ohms. In contrast I believe the input impedance for the mic channels on a Yamaha LS9 mixer is 3k ohms.

The spec sheet for the Shure SM58 say rated impedance is 150ohms (300 ohms actual). The instructions for the EMG GZR pickups say DC resistance is 11.2K and impedance at resonance is 68K...a bit higher than the SM58.

Something called impedance bridging is typically used. Basically impedance bridging means the input/load impedance is way higher than the source impedance. A general rule of thumb is impedance bridging occurs when the load impedance is at least 10 times the source impedance. I believe the intent of impedance bridging is to make the impedance high enough that the source views the situation as if there is no load, I.E. an open circuit. If the input impedance drops too far, it will load down the source.
 
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#11
You might not want to hear this (which I say because I was in a similar boat a few months ago, and I didn’t want to hear it), but you’ll probably get a better sound recording with plugging your bass via your instrument cable directly into the instrument input of the audio interface. I say "probably", not "definitely" - try both and decide for yourself. On many amps, the onboard DI Out isn’t the best. Every amp is different, of course.

Anyway, with my amp’s DI, the sound quality is a little soft and blurry, so I’ve finally come around to plugging direct to the interface with my instrument cable (no amp). From there, you can EQ the sound to roughly simulate an amp, or you can use [software] "impulse responses" to really sound like a particular amp.

There are other ways to record bass too, of course, such as using a mic on a cab or using a dedicated recording direct box, etc. Anyway, not to throw to much at you - just saying plugging right in with your instrument cable (about the easiest thing you could do) might give you a better result. But the main thing is just to plug something in, hit record and see what happens!

Have fun with it :thumbsup:
 
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#12
The term "Z" regarding to these matters is synonymous to impedance. XLR Jacks on amps, DI's, etc are "low Z" and instrument cable jacks are high "Z". Most amp XLR outputs don't have the 48v output voltage like a mixing board to power microphones (unless specifically designed to support a mic), so you can safely run an XLR mic cable to devices with XLR jacks. If you're still unsure you can look on your amp manuals to verify their output.
 
#13
Some interfaces allow you to use the XLR input for line level or mic level. You just have to select it in the software. Not all let you do this.

But even if your interface doesn't allow you to select line level for the XLR, in my experience it doesn't add much coloration to just use the XLR anyway. If you you turn the interface preamp's gain down, it will accept the di signal just fine and sound about the same.
 
#14
KohanMike said:
Patti, from what I understand, mic level and line level refers to the impedance of each, not the volume.
Click to expand...

Wrong, it is the level. Line levels can be either -10dB (sometimes called "consumer", what you would have from a home stereo tape deck or CD player output, typically RCA jacks) or +4dB which is almost always on balanced XLR, sometimes 1/4" TRS. Microphones put out significantly lower levels than -10dB. Plugging a +4dB output into an XLR meant for a microphone will easily overload the preamp.

Read the specs of the interface to see what the maximum input levels are for each input type.

EDIT: I should have mentioned this when I first posted. Just because an amp (or any device with an XLR output) has an XLR output, it doesn't mean that it is always mike level, it could be instrument level or line level. Read the specs in the amp's manual to determine the output level.

For home recording beginners, it's best to record direct from the bass to the audio interface. Worry about recording amps after you have some experience. Most audio interfaces today will have a switch for this purpose, again check the manual.
 
Last edited:
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#15
Wasnex said:
Mic, instrument, and line level refer to signal levels. Per the linked article mic level is about -30dBu, instrument level is about -20dBu, and line level is about +4dBu. Line level, instrument level, mic level explained

You could also could convert the dBu levels into voltage levels.

These are general terms as hot mic level crosses into instrument level, and hot instrument level crosses into line level.

Regarding balanced versus unbalanced. Instrument cables have two conductors. One of the conductor is grounded and the other carries the signal. Instrument cables are coaxial, so the ground is wrapped around outside of conductor that carries the signal. This called a shield and it is designed to help reduce induced noise.
View attachment 3860337


Mic cables have three conductors. Two conductors carry the signal and they do not have to be referenced to ground, so they essentially float. Because the two conductors are parallel they benefit from what is called common mode rejection. Essentially if a voltage is induced in one cable, the same voltage will be induced in the other cable so it cancels out because there is not voltage differential. The third conductor is the ground. A mic cable is coaxial like an instrument cable so the grounded shield is wrapped around the two conductors that carry the signal.

View attachment 3860338

Images from What’s the Difference Between Balanced and Unbalanced?
Click to expand...

Wait... am I missing something here? In this illustration, the signals appear out-of-phase (which would cancel if summed) and the noise appears additive. Are they summed at the end? Am I seeing this incorrectly?
 
#16
hey there,

i'm also new to the home digital recording thing and have been accumulating gear over the last few months. just yesterday i tried mic'ing my amp for the first time. i have been up till now been guitar-fx-interface-computer. so the signal has been just like running the guitar straight to the interface *my interface has a combi input for either a 1/4" or xlr input. the levels for the di option were loud, in that my gain was pretty much low and even between instrument, fx board, and interface.

yesterday i found out that if i run into my amp and then mic that, i need to crank the gain on my interface to get good levels. almost maxxed out. i haven't tried the xlr out on the amp (rumble 100), so i will do that now just to see what a difference it is.

i guess all i'm saying is: experiment and see what happens!

once i got the levels from the mic figured yesterday, i can honestly say i definitely like the warm tone of the mic'd amp over the di sound. the mic just add something to the tone/mix that is quite pleasant to me. now the only problem is i need to be very selective with my recording sessions cuase the 100 rocks the apartment too much to be playing "live" everyday. so generally i will be recording di most of the time for quietness sake, which really sucks when i wanna rock the house
 
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#17
BassNugget said:
Wait... am I missing something here? In this illustration, the signals appear out-of-phase (which would cancel if summed) and the noise appears additive. Are they summed at the end? Am I seeing this incorrectly?
Click to expand...
The signals are subtracted from each other at the receiving end. Let A be the desired signal and n be the induced noise. Then,

A - (-A) = A + A = 2A
n - n = 0

- John
 
#18
Use an XLR to XLR. (Most amp DIs are mic level.)

But as DMT said, you’ll probably get a much better sound plugging your instrument directly into the MOTU.

As a rule of thumb, the fewer things you have plugged in between your source (instrument) and interface, the better the recording will sound. Think, every effect pedal or preamp will each add a tiny bit of distortion and noise. - Keep it as simple And clean as you can.

If you need eq and effects, use plugins.

If you really want the sound of your amp, put a mic infront of it.
 
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