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Distortion in upper frequencies from bass pickup

Discussion in 'Amps, Mics & Pickups [DB]' started by Kerrie, Dec 7, 2016.


  1. Kerrie

    Kerrie

    Dec 7, 2016
    Hi guys! First, I want to clarify that I am not a bassist, but an audio engineer in a jazz club, so double bass is a hugely important part of my work! I have a distortion problem that seems to be following me, and I'm having a hard time troubleshooting it. I'm hoping you can help me.

    In my club, we have one bass in particular that is our house instrument and another that serves as a backup. The primary bass is a vintage David Gage, and both have relatively new Realist copper pickups. i usually run a mic and a DI on bass, and blend the two sources to taste. But I take an extra step (due to the acoustics and PA setup in my club) of splitting the DI signal into a high and a low, so that I can reinforce only what is necessary, in the appropriate amounts, to supplement the natural sound in the space. The DI I use for this purpose is a Radial PZ, specially designed for piezo pickups. The problem I'm having is distortion on the DI channel. It is primarily in the higher frequencies, so when I split my DI signal, the low one sounds ok, and the high one can be so bad it's unusable. It seems like there is a very low signal threshold under which the signal sounds great, and then quickly distorts. I have bypassed the DI box, tried different quarter-inch cables, different amps, and even switched out the basses. It ALWAYS comes back. Which leads me to believe there is an issue involving the pickups - not necessarily a problem with them, but an impedance issue or perhaps an issue with the fit of the pickup against the bass or the bridge. Like that certain frequencies end up going into the signal chain way too hot. Has anyone experienced a similar problem, or have some ideas as to what I can do? Thanks so much!
     
  2. The Realist is a rather dark pickup with very little high frequency amount. It is also known, that the pickup typically lasts about five years until it is damaged due to the high pressure. So it might be that both pickups are damaged.
    The Realist also doesn't sound good in louder situations.

    I didn't understand exactly how you split the low and high frequencies (of the Realist DI after the Radial PZ, I assume), so I cannot say if there might be something wrong.

    If you can borrow a different double bass pickup that could be easily installed, you might test with it if the problem persists.
     
    Ric Vice likes this.
  3. RRR

    RRR

    Feb 18, 2016
    NYC
    How exactly are you splitting the DI signal into high and low? What happens when you just take the Realist as one channel full range?
     
  4. Kerrie

    Kerrie

    Dec 7, 2016
    Well, I am double-patching the channel, and low-passing one channel to be my "meaty" part of the signal, and high-passing my other to be my pluck and definition. Lows and low-mids tend to hang out in my room, so it really helps me to be able to bring up just the part of the sound I need - there may be plenty of bass sound in the house from the stage, it just needs a little help to poke through the mix, so my high channel allows me to do that without just making the whole thing louder. When I take off the pass filters and listen to the whole signal, I still hear the same distortion. It's just a bit less obvious. It sounds like really awful clipping, only nothing appears to be too hot anywhere in the signal chain that I can see.
     
  5. Kerrie

    Kerrie

    Dec 7, 2016
    Thank you! It's good to know that about the Realist. Since those are the only pickups we have, and by far seem to be the most popular with artists that bring their own basses, I don't have a whole lot of other products to compare it to.
     
  6. Have the Realists been properly fitted to the bridges/tops by a luthier? I was having some problems with my Realist and my luthier re-fit it with a wedge stuck between the legs of the bridge to spread them apart as they are under load. It made a HUGE difference in the clarity of the signal, and frankly the clarity of the bass. Also from that experience, I know there can be issues with the edges of the copper foil vibrating against the top and causing noise that can sound like high-frequency distortion. I'm still not a huge fan of the Realist, but a proper fitting saved me from spending $300+ on yet another pickup and installation.

    Also, the Realist can have a pretty hot output. Have you tried padding the signal at the DI? I have to set the gain on my amp a bit lower with the Realist than I have with other pickups.
     
  7. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    Yeah,
    I'm afraid you're dealing with the achillies heel of the Realist. While it works nicely into an amp at moderate volumes, when you run it FOH at higher volumes it tends to sound nasty. There are better choices now, but the Realist was a godsend when it first arrived on the scene. IME you should just buy a DPA 4099Dvote and be done with it. Just my take.

    Ric
     
    Last edited: Dec 9, 2016
    MR PC likes this.
  8. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    Upper frequencies, as in 1-4 kHz? The pigtail lead from my BP-100 was vibrating and causing some distortion until I tied it down. I've also had to add a bit of foam at the jack to dampen vibration.
     
  9. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    Ok Crum
    We were discussing the issues with a Realist in this thread. Ye Old BP-100 is an entirely different "can 'o worms. IME it's time has come and gone. Just my take however. The more you can do to isolate any pickup the better it will sound. The lead on an Ehrlund EAP has to be carefully isolated from the top and tailpiece.

    Ric
     
  10. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    My point was that the lead from any pickup can act as an additional capacitive pickup, superimposing a second signal on that of the original pickup, regardless of brand. ;)

    This is the source of the distortion I found at high frequencies, which was addressing the original question. The length of cable involved was about 4".
     
    Ric Vice likes this.
  11. Kerrie

    Kerrie

    Dec 7, 2016
    Wow, you guys have been very helpful! Thanks for giving me all of this to consider. Gives me some stuff to work with. :)
     
  12. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    Agreed,
    The Realist has a little rubber band that allows you to loop the lead so it doesn't make contact with the table. It coils the lead so it doesn't touch the top. That helps
    a lot, with vibrations influencing the signal coming from the pickup's lead. The best product I've seen, would be the cable they use for the DPA 4099. It's very thin and light, yet
    vibrations don't seem to travel through what I've been told, is kevlar. Whether or not you could use it with a piezo transducer, I have no idea. I know that Goran Ehrlund had to
    upgrade the quality of the lead, coming of the EAP, because it was incredibly noisy, partly I think because it was very long. The best leads I've used, were the ones off the MSP
    pickup, very substantial. Unfortunately, the BP-100 besides being noisy, also had to have a separate gound wire as well, where it's counterpart, the Underwood did not, because it's lead was better
    insulated. Just my take.

    Ric
     
  13. seamonkey

    seamonkey

    Aug 6, 2004
    That's hard to do, there is always a phase difference between the mic and pickup. Phase differences can cancel frequencies you want and reinforce others you don't want (Combing). It shows up worst in the higher frequencies. Try just one or the other.
     
    Ric Vice likes this.
  14. That's the reason why the pickup often only reinforces the lows or the mic only the highs that the pickup cannot reproduce. If the mids that are present in both signals are mixed, you will get the unwanted comb filter effect to some degree.
     
  15. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    Lead quality is mighty important in this and most MI applications, as the gear is subjected to what amounts to constant vibration testing. ;) You already know from the need for the rubber band that even with good cable, you can still get problems from resonances at certain notes.

    I wondered about that ground lead on the BP-100. It might help in high RF urban environments, because of the high impedance involved. It seems a holdover from slab thinking, though.
     
  16. If it's two signal wires and a shield it might be a differential signal, at least if the amplifier following uses the the two signals that way.
    By grounding one of the signal wires you get a single ground related signal that is more sensitive to electric noise than the differential one.
     
    Ric Vice likes this.
  17. RSBBass

    RSBBass

    Jun 11, 2011
    NYC
    No helpful suggestions but a shout out to the OP for caring about the upright bass sound. All to often you hear us complain about house gear and sound guys. Here is one who is trying to do the right thing, kudos.
     

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