I am using an M-Audio Delta 1010LT to record a garage band. To capture my guitar, I run a line out of my guitar amp into one of the line inputs on the interface. But the levels are extremely high, even when the fader for the channel is all the way down in the Delta 1010's software mixer.
There doesn't seem to be a way to reduce the level coming out of the guitar amp, so I was wondering if using a DI box will enable me to get a usable level for recording. If so, should I go for a passive or active DI, and are there DIs with unbalanced outputs, as my interface has RCA inputs?
Alternatively, would a simpler solution be to buy a preamp?
Daniel McShane
In a guitar amplifier's circuitry, the line-level output (marked 'pre out' in this case) is typically situated before the main amplification stage, meaning that changes to the master output have no effect on the line-level signal. Editor In Chief Paul White replies: Firstly, I'm assuming that, when you say "I run a line out of my guitar amp" you mean from the preamp output of your guitar amplifier, not the speaker output, as the latter signal could damage your recording gear.
I'm also assuming that your preamp stage comes before the output stage — meaning that the output volume control doesn't affect the level of the output signal — as that's the normal arrangement in the vast majority of guitar amps.
Assumptions considered, the most obvious solution is to reduce the input gain of your amp — unless, of course, you're intentionally boosting it to force distortion. Doing this should reduce the level that's present at the preamp output, but still permit you to make up gain using your master output control, with no affect on the preamp output.
However, I suspect that you are indeed overdriving the input stage of your amp, as you describe yourself as a garage band!
Most DI boxes include a pad switch to reduce the level of the incoming signal and for your purposes, either a passive or active version will do fine. If possible, get a model with a variety of pad positions, as this gives you a better chance of finding a good level match. DI boxes generally have balanced outputs, as they are designed to plug into mic inputs (not line inputs), and active models can often be phantom powered from the mixer or preamp to save on batteries.
If you only need to reduce the signal level and you can handle a little basic DIY, you could just use a 10kΩ logarithmic potentiometer — available from the likes of RS Components (http://rswww.com), Maplin (www.maplin.co.uk), or Farnell (http://uk.farnell.com) — fed from your preamp output, and take the output from this to your interface.
A DI box, such as this Radial J48 (reviewed on page 132 of this issue), splits a guitar signal so it can be fed to both an amplifier and a preamp that accepts mic-level inputs. This model has a 15dB pad, which allows the user to control signals that are too hot. Buying a preamp is a viable alternative, as is feeding the signal into your interface 'clean', then using a software amp-modelling package to add some grunt, but if you like the sound your amp makes, why not mic it up? This approach will give a much more natural sound. Furthermore, if you're DI'ing from an amp that doesn't have a built-in speaker simulator on the preamp output, overdriven sounds are likely to sound very thin and edgy, as they don't have the character of the speaker to smooth them out. You can fix this by using the speaker simulator part of a software amp modelling plug-in, but again it may not give the same sound as miking your amp. If you haven't tried miking before, you can have a go with any mic you happen to have to hand, and place it close to the grille-cloth midway between the centre and edge of the speaker. Moving it closer to the centre gives a more focused sound, while moving to the edge gives a more open, slightly warmer sound. However, speakers and amps vary, so it's best to experiment with mic placement. Different mics produce different results, but almost anything will sound better than DI'ing, unless the amp has a recording output with speaker simulation.
While we're on the subject of recording guitars into a DAW, here's a tip: record the guitar with less overdrive than you think you'll need, so you can add more if necessary using an amp-modelling plug-in.