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Recording bass DI

Postby BJG145 » Sun May 20, 2012 7:44 pm

I'm making recordings of a bass guitar with active pickups for use with an amp modelling plugin. I gather it's not a good idea to plug electric guitars straight into a desk's Mic socket, so I'm thinking about an MTR DI-3 I've had knocking around but never used, and a Zoom 808II effects pedal which I could put on bypass. Is there likely to be much audible difference between the three options...?
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Re: Recording bass DI

Postby Jack Ruston » Sun May 20, 2012 8:17 pm

The DI plugged into the mic amp is the way to go. The zoom will probably convert to digital even if 100% dry. I'd avoid that approach.

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Re: Recording bass DI

Postby BJG145 » Mon May 21, 2012 7:34 am

(OK, thanks Jack.)
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Re: Recording bass DI

Postby ef37a » Mon May 21, 2012 10:28 am

You say it is an active bass?

There should therefore be no problem in feeding it straight into the mixer/AI line input.

You could go into a mic input if you made a simple resistive attenuator/impedance balanced circuit. The problem with a passive DI for bass is limitations in the transformers unless they are expensive, at low frequencies but then since there is not much below 80Hz from a standard 4stringer that might not be such a problem, you might even like the added harmonic "growl"!

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Re: Recording bass DI

Postby Shivanand » Mon May 21, 2012 6:36 pm

ef37a wrote:but then since there is not much below 80Hz from a standard 4stringer that might not be such a problem, you might even like the added harmonic "growl"!

Dave.

Maybe there isn't much below 80Hz if you don't use the E and A strings. Most bass players I know use all the strings and they like to hear the fundamental frequencies, as do I!
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Re: Recording bass DI

Postby BJG145 » Mon May 21, 2012 6:51 pm

I'm also trying to educate myself here. I was aware of the impedance-matching issue, though I don't understand the science behind it, but I hadn't considered the D/A conversion aspect.

Does this mean that, if you used a non-valve amp, you'd also have an unwanted D/A conversion, as with a digital FX box...? (Because I was also thinking of taking the signal through my Ashdown bass amp and using the DI from that.) Would there be a difference between using a valve amp as a "pre-amp" for an electric guitar and using a non-valve amp...? I know people are very choosy when it comes to vocal mic pre-amps, but I haven't noticed the same attention to detail for DI-ing guitars.

Re: active v passive pickups, this was also in the back of my mind, as I've seen conflicting advice re: running active pickups into a Mic socket.

And now you're saying it also depends whether you use an active or a passive DI...?

D'oh. I need to read a book.
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Re: Recording bass DI

Postby Hugh Robjohns » Mon May 21, 2012 7:13 pm

Guitar and bass pickups are generally designed to work into a fairly high impedance (>250k ohms and often much higher), and can sound rather odd if not loaded properly. The output level is typically around -30dBu or so. Although inherently a 'balanced' device, most pickups are wired into unbalanced circuitry and provide an unbalanced output.

A mic input is balanced and presents a very low impedance (~1.5k ohms), making it wholly unsuited to handling guitars directly. There is also the danger of inadvertantly switching phantom power on which could do a lot of damage to the guitar!

The solution is a DI box that presents a high impedance to the guitar pickup and converts the unbalanced output to a balanced one capable of driving a low impedance load happily. it also isolates the phantom power from the guitar, and often provides a ground lift function to avoid ground loops.

Active DI boxes usually have higher input impedances than passive DI boxes and are generally prefered by most guitarists and bass players.

Some basses have their own active buffer built in. This ensures the pickups see the right load, while allowing the output to drive long cables and lower impedance destinations, often with near line-level signals. So in many cases you can plug directly into a line input quite happily.

There is no digital conversion in most guitar/bass amplifiers, whether solid-state or valve-based. However, those with amp modelling options or some forms of built-in FX will digitise the signal in order to apply the processing in the digital domain.

HTH

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Re: Recording bass DI

Postby BJG145 » Mon May 21, 2012 7:37 pm

OK! Thanks for all the info people.
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Re: Recording bass DI

Postby ef37a » Mon May 21, 2012 8:16 pm

Shivanand wrote:
ef37a wrote:but then since there is not much below 80Hz from a standard 4stringer that might not be such a problem, you might even like the added harmonic "growl"!

Dave.

Maybe there isn't much below 80Hz if you don't use the E and A strings. Most bass players I know use all the strings and they like to hear the fundamental frequencies, as do I!
Well I based that statement on the position of the pickup and the position of string strike but I also just did a test with a P bass copy plugged into the high Z input of my ZED10. Plucked at the thumbrest the E string is 6dB higher at 80Hz than at 40Hz and 120Hz is 6dB down on 40Hz.
Plucked at the octave, 40Hz is some 12dB higher than 40 and strangely 120Hz is 6dB higher than 80.

There was more 40Hz than I expected but then the bass was far from new when I bought it 20years ago and it still has the same strings on it! A new set would I am sure be brighter(1kHz is 36dB down on 40!). Then the use of a pick will surely result in less LF?

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Re: Recording bass DI

Postby BJG145 » Wed May 23, 2012 7:02 pm

I know I'm being dense here but...

OK, so I've got this MTR DI-3 box which states that:

If needed, a second mono jack-to-jack lead can be connected from the Link socket to the input of a combo, so that the musician can monitor himself on stage or in the studio.

The balanced XLR Output socket (pin 2 hot) should be connected via a balanced 2 core screened lead to the stage box, or input socket of the mixer.


http://www.mtraudio.com/user_guides_current_di2&3.htm

The mixer has Mic XLR inputs and Line 1/4in inputs. So do I have to use an XLR -> Jack cable to go from the DI box to the Line input...? Or an XLR cable to go from the DI box to the Mic input? Or can I use a jack-to-jack to go from the Link socket on the DI box to the line input.

The DI box also has a ground-lift switch, which I'm guessing I don't need unless there's a problem, and a 0-20-40 three-way switch I'm not sure about which I guess I can just leave on 0.

I've never really got to grips with DI boxes. It's a mental block.
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Re: Recording bass DI

Postby Jack Ruston » Wed May 23, 2012 9:02 pm

Bass to DI with an instrument cable. Pad will depend. If the bass is active you might well need -20, but see how hot it is. DI output to mic amp in with an XLR cable, adjust gain for 0VU average in your DAW...depends on your calibration level, but be aware that DI'd basses and guitars are REALLY peaky, so be conservative. If you're adding 20 or 30 dB of gain at the mic amp and you're very hot in the DAW then click the pad down one more notch on the DI. You're balancing headroom against the noise that the mic amp introduces if you have to crank it too far round. Sometimes 20dB intervals can make you feel like you're in between the sweet spot. Don't worry too much.

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Re: Recording bass DI

Postby Imran500 » Sun May 27, 2012 7:30 pm

Use the Tech 21 VT Bass pedal straight into your desk and then into the Ampeg SVX bass sim. I use an active bass in this manner and you get an extremely good bass sound
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Re: Recording bass DI

Postby BJG145 » Mon May 28, 2012 11:21 am

(I was pleased with the results I got via the MTR. Thanks for the pointers.)
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