Idea for a new preamp system - thoughts from the gearhead elite?

Discussion in 'Amps and Cabs [BG]' started by secretdonkey, Jun 9, 2003.

  1. secretdonkey


    Oct 9, 2002
    Austin, TX
    Got an idea - tell me if it's already do-able with existing technology, simply not practical, or if I should run go patent it before somebody takes the idea and runs with it.

    The idea is for a preamp, or at least a device that would be part of the preamp chain, that could listen and adjust EQ based on what it 'heard' in the room. A small wireless mic/transmitter unit could be placed at some appropriate spot in the room that would 'listen' to the sound of the bass and make EQ adjustments for room acoustics. The unit would know how far away it was from the amp by judging lag in sound or radio waves or something like that, and could make suggestions to move the listening station closer or further away if needed.

    I'm not sure exactly how a user would 'train' the system to produce a sound tailored exactly to their taste (possibly adjustable presets like the Bass Pod or other amp modeller???), but assuming that problem could be addressed, the unit could help the bass sound consistent regardless of venue - it could possibly even work to balance against a soundman's questionable EQ in the FOH mix, under the right circumstances where there's enough sound coming off stage to have an effect on FOH sound.

    I know that years ago a sound company my band at the time used employed a device that produced a reference tone series for calibrating EQ, so I would imagine the technology is available. My tech savvy is pretty weak on these issues, so I don't know where that type of technology is at these days...

    Anyway, how dumb is this idea? Given that I often hear pretty lousy bass sounds at big venues with expensive sound gear and L337 soundmen, it's either a hopeless battle or something waaaayyy overdue...

  2. Mudbass

    Mudbass Guest

    Sorry, but it's already been invented...they call it a soundman. :D
  3. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    I agree about the lousy sound at big venues. I saw Medeski Martin and Wood last night and the bass and even the kick drum often got lost in the mix. MMW was not the headliner, and not using the main mixing desk... maybe that had something to do with it? Regardless, it was disappointing because the band were kicking butt.

    As far as technology goes, I'd envision a multi-mic system, maybe with sampler: have a sample of your ideal tone, a close mic, and and a number of ambient mics spread throughout the room. Finally, a brain to adjust the EQ curve.

    I can also envision the robo-EQ getting into a frequency fight with the live soundman... :eek:
  4. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    There are programmable EQs with built in frequency spectrum analysers that do this. One such unit is Behringer DSP8024. You basically connect a measuring microphone, send out pink noise in the speakers and analyse how to set the EQ to smooth out the curve depending on the room characteristics. It should be possible to use this for the bass only I guess.
  5. BruceWane

    BruceWane Supporting Member

    Oct 31, 2002
    Houston, TX
    What you're talking about is called a spectrum analyzer or real-time analyzer (RTA for short). Most of them have built-in pink noise generators.

    You use them to make a systems response flat throughout its frequency range. You feed pink noise (noise which contains all audible frequencies in equal amounts) through the system. The analyzer then "listens" to the sound in the room and shows the response. Then you adjust out the peaks and valleys caused by the acoustics of the room with an eq. You've probably heard this done at big shows, since they can't accurately eq for the room (or arena) until the place is full of people. It sounds kind of like a hiss, but you can hear a lowness to it.

    I don't know of any system available that actually does the adjustment for you. You'd need an automated 31 band eq to do it properly.'re talking about a good quality bass preamp, PLUS a real-time analyzer, PLUS an automated 31 band eq, PLUS software and a processor to control the whole operation..........I'd say retail should run $3000 - $4000. could do this manually pretty easily. Just get a 31 band eq and an RTA and it's pretty simple.

    Unfortunately, very few soundmen at the "bar band" level have these things. I don't really know why, because they aren't that expensive and they are quite useful.
  6. geshel


    Oct 2, 2001
    You can equalize the volume of frequencies like this, as has been mentioned.

    The RTA/EQ "do it by hand" method has been around for a while. It's also possible to automate these days, likely with an integrated digital unit. Technically, it's a problem that the DSPs in many effects processors could probably handle. It would only be costly (>$1000) due to the new engineering in programming them and stuff.

    One complication is that the frequency response will vary around the room - near corners or walls vs. in the middle, etc - depending on the resonance modes of the room. You can EQ one spot to be flat, but it might make the others worse. With some rooms this could be fine, others not very useful.

    The harder part, is that "boom" caused by the room isn't just louder volume at that frequency, it's delay too (time for the room to resonate). Same problem that boomy speakers have. That's harder to analyze, and even more so to fix. I'm not certain, but I think an adaptive filter could compensate for this. The delay between the source and the mic would complicate things, but I think it could be done. Again though, the sound would be optimized for one listening location, and could sound pretty dreadful elsewhere.

    I thought about doing something like this for my senior project a few years ago when getting my degree. Ended up going with something simpler, but fundamentally flawed: using an adaptive filter to reduce loudspeaker distortion. My partner and I kinda figured out near the end that it wasn't actually possible (using a linear system to compensate for nonlinear behavior - doh!), but all the work for the project (speaker, accelerometer, signal buffering, DSP card, assembly programming) was worthy of a passing grade. :) *cough* won the IEEE student paper contest too! *cough* :cool:
  7. Petebass


    Dec 22, 2002
    QLD Australia
    The problem with these devices is that they all assume that flat is good. It isn't always. I guess it gives you a place to start, but you'll always end up having to use your ears and fingers to tweak things. Trying to automate that process is like trying to built a machine that reads minds.

    Geshel's right about the dangers of optimising sound for one spot. But unfortunately that problem exists at every gig with or without fancy gadgets. As a punter I often walk around the room looking for a spot that sounds the best and it's usually near the desk or side of stage. When I do sound I ALWAYS walk around the room to get an idea of what everyone else is hearing.

    It's a good idea Donkey but it the solution to the problem of "soundguys can't pull bass sounds" is education. Work with your soundguy, talk to him, tell him how you like it, and he'll get the picture eventually. If enough soundguys start to "get it", it's only a matter of time before one of them is mixing at the big shows we're all complaining about now......
  8. BruceWane

    BruceWane Supporting Member

    Oct 31, 2002
    Houston, TX
    Yeah, absolutely, especially when you're talking about a musical instrument amplifier. I'd think the way to use this approach is to eq the system to get as close as possible to the response curve that you already know you prefer from previous tweaking/trial and error.

    I had one soundman who was complaining about the low end from my bass rig. He insisted that I had my eq set all wrong, and proposed to "help me out" by doing the pink noise/RTA thing to it and eq-ing it to a flat response. When he was done I could have loosened peoples teeth with the low end I was pushing. And you could tell that the soundman was almost too proud to admit that he was wrong, but we kinda had a laugh when I asked him if it was OK for me to put it back the way it was because I didn't want to make people sick.
  9. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    I have seen some "automatic" RTA units in the past. I recall Peavey had one (the "Autograph") and maybe Behringer?

    You just hooked up the calibrated mike, the unit generated pink noise (at stage volume sounds like a 747 taking off) and then it auto-tweaked the EQ to "flat". You could then do further manual tweaks and store the whole EQ curve as a preset.