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I was trying to test my new Mackie 402-vlz3 mixer yesterday with a bass guitar. so my friend came with a jazz bass (the brand escapes me now...) and we plugged it into the line 1 input and made use of the instrument level switch (which is great, replaces a DI box). the sound was crisp, clear and very punchy, but there was this really slight, almost inaudible hiss or buzz (I emphasise: it was extremely low, not a big thing) which could be heard every time he took his hands away from the strings, and we both attributed it to static.

I hooked the bass stright to the Mackie (as mentioned), and I went from the outputs into the UNBALANCED RCA inputs in my Juli@ interface. Is it because of the unbalanced cables that I might be getting this buzz? I also want to mention that I haven't got monitors but am just listening everything to a hifi stereo system. perhaps with monitors the buzz would be even more recognisable, that's why I want to get rid of it!

the interesting thing about the Juli@ interface is that it lets you swap it and use instead TRS balanced i/o. should I try buying some balanced cables and go from the Mackie outputs into the balanced inputs in the card? would this help with static?



TheJackAttack Sun, 03/07/2010 - 22:39

When you hook into the Mackie you need to set the channel fader at 0dB and the master fader at 0dB (not pushed all the way to the top). This creates the cleanest path for the signal. Adjust your volume via the trim pot at the top of the channel. Now check to see if you have noise. If you still have noise then leave the the Mackie exactly the same and disconnect the bass cable. If you still have noise then turn the trim pot up and down and see if you get change in the noise level.

The real problem is that you don't know if the noise is part of the bass pickups/instrument cable or part of the mixer or part of the Juli@.

dvdhawk Sun, 03/07/2010 - 23:10

Follow Jack's procedure for setting up your gain structure, that's ALWAYS going to be good advice.

If the bass only makes the noise when he takes his hands off the strings, it's probably a shielding/grounding problem with the bass. Shielding and grounding are usually very easily fixable by a guitar tech.

Even a well shielded guitar or bass can give you fits when it's near a computer. If the bass has active pickups or a pre-amp make sure the battery is good, use a high-quality instrument cable and try positioning the instrument a little further from the computer. (CRT monitors and TVs are nasty noise-makers with guitars.) You may find that pointing the headstock of the guitar a different direction will help. For example, I've seen a guitar buzz like crazy with the neck pointing north, but quiet down considerably pointing northeast. This isn't to say that the compass direction has anything to do with it, it's something else in the environment that is creating the interference and cancelling in a particular position.

I would certainly recommend balancing as many of your connections with TRS cables as a matter of best-practice, but I don't think it will help this particular static problem.

Good luck.

anonymous Mon, 03/08/2010 - 00:46

as suggested by others, shielding/grounding is the most common problem you may find when you link a balanced circuit to an unbalanced one. If the mixer has balanced inputs AND at least one unbalanced output, it is extremely likely that the "unbalancing" bridge is done via a coupling transformer or other sophisticated circuitry built in order to avoid problems like the one you seem to experience. If the output is balanced, and the input you want to link is unbalanced, doing it via a "cross-cable" is, electrically, the very worst solution. Depending on the impedances and a lot of other factors, it may work as you expect, or be terribly noisy, or not be working at all. In these cases, you can very easily build up your own external appliance in order to match the two: there are plenty of resources online, for example
(don't want to make advertizing for anyone, it's just I like the way this paper is written).
However, you don't tell how "low" is the noise with respect to the signal: is it compatible with the application you want? I mean, the In/Out transformers are generally considered a must, but they could very easily turn out into being unuseful for home applications or even for simple staging experiences (depending where you perform... If you're outside, in a noisy-by-nature environment, even a 40 dB S/N ratio will be perfectly acceptable !!!).
Hope it can be useful...

ferchis Mon, 03/08/2010 - 13:56

thanks cloche! the application is simple: RECORDING. I want to get the best signal possible from every instrument. I'm not afraid of synths since they've never given me any problems when recording,their signal is incredibly clear and clean. I haven't tried guitars so far, but I hav to eventually, and I was talking about this to a music shop assistant today and he told me it was most likely a problem withing the bass or the cabling, that I should use good cables and that there might be an issue with the bass itself, which should be corrected by a luthier.

Jack, what is the "trim pot"? the gain lever? is that it?


TheJackAttack Mon, 03/08/2010 - 14:07

Correct. Front top to bottom you have:
XLR jack (mic)
TRS jack (line)
rotary gain (your mic/line preamp)
two rotary eq knobs
rotary channel fader.

The bottom rotary knob should be set at the marking. U stands for unity gain meaning that the VLZ3 is neither cutting nor boosting the signal-both of which can cause noise. The rotary knob to the right that is your "main" mix control should also be set at . Leave the eq knobs also at . You will control your level from the top rotary preamp gain knob and if you absolutely have to monkey with eq do so within your DAW. The rule of thumb is to have your peaks be no more than -16 to -12 dB.

ferchis Mon, 03/08/2010 - 17:22

great, thanks a lot jack, I'll bear that in mind next time we try recording, because I did exactly the opposite: I boosted the level faders and left the gain practically untounched; so you say that I should then try to increase the gain if we feel that the bass is still a bit weak? (though as far as I recall when I activated the instrument level switch-Di box the signal was greatly boosted)

TheJackAttack Mon, 03/08/2010 - 17:34

I'm saying that you set whatever level you need from the preamp gain and leave everything else alone. To set the level you get the musician to play as the loudest section of the music and make sure that the peaks are no larger than -12 dB. Now turn it down a hair because I've never met anyone other than myself who played normally for a mic/level check. Once you have the gain set leave everything alone. Your DI box should be set for instrument level if you are plugging a guitar or bass into it.

anonymous Tue, 03/09/2010 - 00:02

another idea (just an idea... The best recordings I personally did were direct-takes in pure-stereo, so I'm not very qualified as regards multi-tracking... :-) ): if the scope is recording, could you possibly use your audio interface directly and use Sonar as a multitrack recorder? I mean, and provided all the components of your band agree, which is not so "automatic" :-), directly link one instrument after the other to an appropriate input of the audio interface, direct the input to a track in Sonar, arm it for recording. When you have the first track, direct it to an output of the audio interface, while you direct the input to a new track, and so on. Small "glitches" in the synchro between players could be very easily compensated, as well as many other defects, much easier than if everything is played and recorded at once.
In order to do so, however, you have to check if the input(s) of the audio interface are electrically compatible with your instruments (impedance, sensibility, etc...): I know nothing about Juli@ (the only AIs I'm used to are some of the Terratec brand), so I really can't tell.
I recognize that very few computer audio interfaces of "non-pro" level offer decent preamp stages, so it may be that controlling gain with the AI directly could end up being a worse solution than interposing the mixer in between...

jg49 Tue, 03/09/2010 - 03:57

The Juli@ has no preamps, so you can not control gain levels with the interface. All control of input gain is in the Mackie and now that the proper gain staging has been explained I believe Ferchis "noise" will either disappear comepletely or be relegated to acceptable levels. If not then the suggestion re: the actual instrument (bass guitar) is the most likely source.

hueseph Tue, 03/09/2010 - 11:22

dvdhawk, post: 343624 wrote: This is all good discussion, but I still think that quote is the most relevant clue in the original post.

...almost inaudible hiss or buzz ...which could be heard every time he took his hands away from the strings....

Yup. Gotta agree with dvdhawk here. Actually, there is nothing wrong or out of the ordinary going on. Even if the bass is equipped with humbuckers, you will get noise when you take your hands off of the strings. The reason being, that the pickups are grounded to the bridge. This is normal. All guitars, bass or otherwise are wired this way.