clueless recording question regard XLR out from amp to interface

Which one to use depends on the output level of the source. If it is mic level, use XLR-to-XLR. If it is line level, use XLR-to-TRS 1/4".

- John

 

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.

 

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.



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.



Images from What’s the Difference Between Balanced and Unbalanced?

 

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.

 

I use a MOTU M2, XLR cable out of my MarkBass and XLR to the M2 input. There’s no mystery. Just get a XLR cable and that’s it.

 

SOP with your gear would be: bass > head > motu (via "mic cable") > computer (via USB). your interface accepts two balanced inputs so you can record voice (or other) concurrently. good luck with your gear and your recordings!

edit: as Igor Porto stated.

 

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

 

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.

 

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.

 

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.

 

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?

 

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

 

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

 

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.

 

Oh OK! Phew! Thanks for that!

 

this is handy ...

Yamaha sound-reinforcement-handbook.pdf

good explanations with diagrams