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Dirt + DI (seems to)= ****. Why?

Discussion in 'Amps and Cabs [BG]' started by SwamiRob, Dec 28, 2019.

  1. Hey there. I've been using some sort of dirt in my chain for a little while now. Not until I've started doing some home recording, have I realised how appalling this (in my case) seems to sound through my amp's DI, and how much of a pain in the arse I must have been for soundguys over the years.

    There just seems to be an un-LPFable offensive fizz that effects the whole signal. I've tried to tame it, but even with quite extreme cuts it's still a pretty unpleasant, and very dull, signal.

    The signal chain I'm currently using, should cut a fair amount of top end before it even hits the amp too. I currently use a VFE RUP which is a multiband distortion + clean blend, with effects loops for bass, mids, and top end. I'm currently not using any of the onboard dirt, and using a fuzz in the midrange FX loop, with the high mids cut down almost as much as it'll let me for a bit of a low-mid midrange growl.

    Sounds great through the cab, and as described above through the DI...

    I'm using an Ashdown ABM500 at the moment, both post & pre-EQ DI signals sound bad with the post-EQ sounding worse. Use a little bit of the "valve grind" to drive the clean signal slightly and make it merge with the dirt better, but even without that on it still sound awful.

    So, without using mics, what are the best live sound solutions? Really don't want to resort to giving soundguys a clean bass sound, because there's loads of bits that I need to keep heavy when my guitarists are playing higher or more melodic stuff.

    I'd rather use a mic all day, but it's not gonna happen every gig I imagine. Would a DI box with some good speaker sim options work?

  2. JKos


    Oct 26, 2010
    Torrance, CA
    Yes, it should.

    - John
  3. Wasnex


    Dec 25, 2011
    Distortion is primarily clipping. Clipping produces a lot of overtones which are essentially high frequencies. If you are using a traditional cab that does not have tweeters or mid drivers, it functions as a natural LPF and limits how much of the overtones you hear. This provides a contoured frequency response instead of a flat frequency response.

    In contrast to traditional cabs, DI's are pretty flat. So if you set up your pedal board to sound good through the contoured response of your speaker, it's going to be extremely bright and fizzy through the DI.

    In my experience most OD and distortion pedals can be dialed in to sound really good through a full range flat response system. Of course if you set up your pedals to sound good through the DI, it's going to sound dark and muddy through a traditional speaker.

    If you can find a DI that has a speaker SIM the goes a good job emulating your cab, it would probably be a huge improvement.
    The OmniCABSIM gets a lot of respect: https://www.dsmnoisemaker.com/omnicabsim-deluxe/yh0m9

    Over recent years, something called Impulse Response (IR) has started to become popular. Basically an IR is digital modeling that can emulate both the cab and mic in an acoustic space. It supposed to be a lot more authentic than a speaker SIM. Unfortunately Bass specific IR is still sort of a wild frontier. Here's an article: Quick Guide – Bass Impulse Responses

    Two Notes is not mentioned in that article, and they have some Bass Specific IR gear.
    Torpedo C.A.B. M, the cab sim pedal from Two notes Audio Engineering.
    Here's a video
  4. Cheers for the responses guys.

    I've tried to cut out alot of that harshness, but like you say it probably isn't quite enough. The LPF before my fuzz is probably about 400hz @12dB per octave, but obviously this isn't doing enough! No wonder sound guys hate dirt on bass when we go into them if it sounds as bad as mine with so much high end taken off, nevermind without.

    I'll check out those suggestions though thanks, the Radial JDX48 looked like an interesting box too.
    DJ Bebop likes this.
  5. monsterthompson

    monsterthompson The Eighth Note Wonder Of The World Supporting Member

    Nov 25, 2008
    An LPF should be after the fuzz. 400 Hz is really low. You should be seeing something closer to 1 kHz being plenty, though possibly as high as 4 kHz.

    Think of a speaker as a mechanical LPF, limiting how much high end gets amplified. For example, an Ampeg 810 has a useable frequency range that reaches 5 kHz. Using an electronic LPF should try to replicate this.
    Last edited: Dec 28, 2019
  6. I was under the impression that most dirt pedals had a pre gain HPF and post gain LPF anyway? I'll have another go at trying it the other way round, but I seem to remember the thing being ridiculously bright when I did last time. I know the basic theory is that you need the higher frequencies in there to clip it to begin with, then you dial out the harshness for dirt pedals. Just didn't seem to work, I'll give it another go!
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    When running a parallel signal path like this, it's possible that unintentional phase shift (it that combined with a polarity inversion) can result in a combined signal that sounds terrible.

    Often, a simpler signal path works better. Have you considered something like one of the Darkglass distortion pedals as a more integrated solution?
  8. monsterthompson

    monsterthompson The Eighth Note Wonder Of The World Supporting Member

    Nov 25, 2008
    Most pedals have EQ but not HPF or LPF built in. At least not user controllable. You might get a HPF “depth” control to adjust the amount of low frequency content entering the clipping circuit.

    Also, you don’t necessarily need the higher frequencies to cause the clipping. A fuzz or distortion pedal will distort everything that goes in, low or high. The question is what proportion of high and low frequencies goes in and gets clipped. Distorted lows sound different from distorted mids, and both sound different from distorted highs.
    DrMole likes this.
  9. Wasnex


    Dec 25, 2011
    Each pedal tends to be unique, so don't assume pre gain HPF and post gain LPF.

    IMHO you should set your LPF at a frequency that emulates the natural roll off of whatever speaker you are using. The idea is for you DI and speaker to sound as much alike as possible.

    I believe your basic idea of how a distortion pedal works is a bit backwards. In general, low frequencies will clip first. When the clipping occurs, it shifts energy to a higher frequency spectrum. This is why the low end tends wash out if you use really high levels of distortion.

    If an OD or distortion pedal has an HPF it's going to reduce the lows the pedal can produce, regardless of the level of drive. A built in HPF is pretty common with guitar pedals to clean up to low end, but it will probably thin out a bass too much.

    A common solution for bass is to split the processing into two channels, one clean and one distorted. Then, blend the two channels back together post distortion. You get the full low end response from the clean channel and the nice distorted texture from the OD channel. For further improvements, you can apply a HPF to the distorted channel so it does not effect the fundamental, and compress the clean channel so it integrates better with the distorted channel. You can do more processing if you like, depending on the sound you are chasing.
    monsterthompson likes this.
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Whenever you split a signal into parallel paths, relative phase and polarity become essential, not just important
    ThisBass, n1as, DJ Bebop and 8 others like this.
  11. What got me about the video was that every time the player did a ‘twiddly bit’ that I would have liked to watch his hands instead we got a picture of the pedal!! :(

    As for dirt, I grew up with low powered tube amps that gave nothing but dirt! It took me a long time to get rid of the damn stuff and get the clean sound of the bass at the volume I wanted.
    DJ Bebop likes this.
  12. bbh

    bbh Supporting Member

    Sep 27, 2011
    Sounds like your issue is with the treble and upper mids. That harshness is being rolled off due to the bass cabinet’s limitations. Not so through hifi. Have tried to seriously tame the highs and work on the mids tone!
  13. seamonkey


    Aug 6, 2004
    Good amp sim, DI, and IEM monitors.
    Many great preamps out there that actually have high quality DI after the signal processing (dirt and eq).

    And don't be afraid of using a PC or iPad, they are on many stages and FOH these days as well as all the recording studios.

    What you get in the studio you can pass to the FOH engineer and they'll have a better idea of what to do with it FOH.
  14. Hundred proof

    Hundred proof

    Apr 22, 2018
    I need the old school dirt in what I do, and work to get it using new school gear.
  15. pbass2


    Jan 25, 2007
    Los Angeles
    My solution for dirt to the FOH, because I almost always end up using backline, is I use my Xotic BB into a Radial JDI, and that's it (except for my tuner). Works a charm, and the BB is so simple yet so flexible. I know how the different settings sound in my studio, so I know what FOH is getting is solid and easy to work with. Granted, this is for an always-on dirt tone.
  16. Balog


    Mar 19, 2009
    Mukilteo, WA
    I mean, if you like your amp’s sound and are going to the PA anyhow just get an e609 or equivalent and plug the XLR into that instead of your DI. Not sure why the simplest and easiest option isn’t even being considered?
  17. RudyTardy

    RudyTardy Supporting Member

    Aug 20, 2002
    Los Angeles
    THIS! Multing a signal and processing different bands separately is difficult enough in the studio, let alone a live situation. Phase coherency is extremely crossover and time domain dependent. Andy’s suggestion of going simple with one chain and a darkglass pedal is a good place to start.
    agedhorse likes this.
  18. Wasnex


    Dec 25, 2011
    IMHO it's not really that big of a deal most of the time. Some pedals do introduce polarity flips and latency which can cause problems. Also EQ and filter circuits introduce phase errors, which may or may cause noticeable signal degradation. Basically be aware of potential problems that can degrade the sound, but I wouldn't let it stop me from experimenting.

    There are plenty of pedals on the market that use internal dual channel clean/OD processing. There are also some that split the spectrum using internal crossovers and apply EQ to each band. Then each band is sent to it's own OD circuit, and finally combined down to one composite signal.

    Another useful idea to explore is the different results you get when the EQ is post distortion versus pre distortion. There are some distortion pedals that split the circuit into three paths and then give you the option of applying the EQ pre or post distortion.

    Lot's of crazy ideas and some of them actually sound really great.
    Omega Monkey likes this.
  19. micguy


    May 17, 2011
    I use relatively little overdrive, so I don't need a lot of filtering to remove fizz, but it still sounds better if I cut the highs some. I have a low pass filter at the END of my chain - after the dirt; it also cuts a bit of hiss in that location. As I play ampless, I think of the overdrive as my "amp' and the low pass filter as my "cabinet".

    The more gain/dirt you put in your signal chain, the more you need a steep cutoff after it to de-fizz things. Some pedals, like Darkglass's stuff, have some filtering on board - that may or may not be enough for you.
    Wasnex likes this.
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I deal with parallel signal path issues fairly regularly when troubleshooting customer problems. It's a big deal if you don't understand it.
    ThisBass, RudyTardy and Balog like this.

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