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Mic'ing guitar/bass amps

Discussion in 'Sound, Music, and Intercom' started by tech2000, May 18, 2009.

  1. tech2000

    tech2000 Active Member

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    I'm curious, which is better?
    Mic'ing amps or using the direct out from the amps directly in the system.
    I usually just mic the amp, but I would like to know other opinions!
     
  2. waynehoskins

    waynehoskins Active Member

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    Electric guitar, your choices are mike the cab or use an amp modeler (which some guitar players like but most generally don't). The sound of electric guitar comes from operating a tube amplifier outside of its linear range, introducing different kinds of harmonic distortion products and 3/2-power-law compression. The output transformer and loudspeaker cabinet also affect the circuit's response, but you can theoretically get close but not quite there by using a FET-based circuit. And since the sound comes from overdriving different amplifier stages, you can't turn it down; it has to run pretty much all the way up.

    Bass, you can go direct -- a bass amp is rarely operated out of its linear range. Also, many bass rigs have a balanced direct output on them so you don't have to eat up a DI.
     
    Last edited: May 19, 2009
  3. NickJones

    NickJones Active Member

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    Just out of curiosity being a lighting guy, I have asked this question to our audio guy, who didn't give me a straight answer, why do some people put mics like 57's & 58's in front of guitar amps instead of using the direct output? Seems like a waste of mics to me.
     
  4. Eboy87

    Eboy87 Well-Known Member

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    For the exact same reasons waynehoskins said. A large part of a guitar's tone comes from not only the amp, but the speaker in the cabinet as well. The speaker loads down the output stage differently than it would driving the direct out, which affects the tone of the signal.

    Also, when using a mic rather than the DI on the amp, you have an entire palate of tones you can get by using different mic positions. My current favorite is a Sennheiser 609 three inches from the center of the dust cap, about a third of the way down.
     
  5. waynehoskins

    waynehoskins Active Member

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    You could also argue that with electric guitar, the amplifier-and-loudspeaker are the instrument, and the guitar and pedals are only a means of controlling the instrument, much like the keyboard and hammers in a piano or the keyboard and valves and air supply in an organ.
     
  6. jkowtko

    jkowtko Active Member

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    I think it just depends on what sound you want. Between effects boxes, reverb, and type of micing, there's a lot of flexibility.

    I guess from my perspective I could ask why you use all those different types of lights ... won't just one type of light fixture do? ;)
     
  7. Dover

    Dover Active Member

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    The best answer I can give is that it depends on how the guitar amp is used. If you are dealing with rock n' roll or heavy metal then it will most likely be like waynehoskins said the over driven amp will be part of the "sound" and you will need to mic the cab. However if we are talking about a guy using an amp at moderate volume to make his acoustic guitar louder than a DI is just fine. In cases like that, unless they are dead set on having an amp on stage, I will take the guitar through a DI straight in to the system and feed the guitar back on the monitor. Saves space on stage and makes the show look better (big guitar amps do not really fit with folk music)
     
  8. rwhealey

    rwhealey Active Member

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    I agree on the "it depends"

    We just had a group from India in and the electric guitar player wanted to use a DI. We pulled out a Radial JDI and it sounded great.

    However, there are many situations where I've miced amps. The amp does contribute a lot to the tone of a player. It's really their call.
     
  9. gpforet

    gpforet Active Member

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    Especially for musical theatre where there is a live band, volumes can get a little uncontrollable. If I need the tone from a mic'ed amp, I'll often locate the amp in an iso-box either under the stage, or down the hall from the dressing rooms, mic it, and then provide the guitar player with a wedge, thereby letting them crank their amp but still have control over the stage and house volume levels. I've been suprised how little volume a guitar player needs in the wedge to get the guitar strings to feedback for those over the top solos.
     
  10. NickJones

    NickJones Active Member

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    I learned my lesson today. I mixed for a tallent show. Used 58's on 2 of the Amps, and a DI on the other, it didn't work during testing, turned out the Bass player (Bassist?) hadn't turned on the amp. Did everything fine untill they changed guitars on one of the amps. Went from electric to electric accoustic, it souned alright untill the guitarist started to play louder, and then it seemd to jump a pitch. it wasn't DI'd. I don't know what caused it, I presumed it was the effects pedal between the Guitar and the Amp, so I unplugged that, and the problem stayed. In the end they turned there Amps up so loud, that I couldn't get the vocalist loud enough to be heard without it feeding back. I would probably have been better to run that guitar strait into the audio snake, but I winged it, and I don't usualy do Audio unless I have to. Thanks for your advice,
    Answered one of my "Why would they do that questions" so why don't they make processors to take your guitar input, give it the sound quality it needs and then output it as XLR? Sureley it would be cheaper than an amp?

    Nick
     
  11. waynehoskins

    waynehoskins Active Member

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    They do .. but .. they're not quite ready for prime time.

    Part of the problem -- the large part, in fact -- is the difficulty of modeling the desired transfer function. It's a complex thing because it's not just EQ or dynamics, it's also addition and subtraction of harmonics, and the prevalence of various harmonic series is dependent on how how hard you hit the guitar. Among other things.

    A 50-year-old tube circuit does this perfectly, but we can't accurately simulate it with DSP yet. So it makes much more sense (especially to the musician, since the amp is a critical part of his instrument) to mike a low-power amp. Remember, a guitar amp has to be cranked up WFO, and even five watts of guitar is really really loud.
     
  12. NickJones

    NickJones Active Member

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    Thanks for all your answers! Now I know why Audio guys do what on the surface looks like they ran out of DI's. So why can you plug a big pair of headphones into the headphone output and it works?
    Nick
     
  13. TimmyP1955

    TimmyP1955 Active Member

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  14. Grommet

    Grommet Member

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    Just micing the amp gives you exactly what the amp is outputting. I have heard of some performers cutting slits in the speaker cone of the amp to give it a special sound.

    I have seen players with a 2 amps, one being a marshal and the other being something old, unmarked and found in a basement.

    a DI on an amp would end up taking the sound before its fully molded.
     

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