Bi-'amping' and compression

Discussion in 'Effects [BG]' started by TraktorBass, May 22, 2021.

  1. TraktorBass


    Mar 9, 2017
    Hey TBers

    Looking for advice on using compressors on a split signal chain going into one amp. Not technically bi-'amping', but dealing with compression on separate signals. I never used compression much, let alone on a complex signal chain.

    My signal chain is clean bass into a OBNE Signal Blender which splits the signal into three separate effect loops. Lets call them Clean, Dirt and Synth. These three loops can be run in parallel or any mix of the three. Usually I keep Clean and Distorted on always.
    • Clean 'loop' is clean. Keeps the low end untouched.
    • Dirt loop goes through two dirt boxes, sometimes with ambient reverb and a chorus/vibrato. Little low end.
    • Synth loop goes through a synth pedal (duh). Alternately a fuzz. Little low end.
    So three very different signals going on.

    The three loops are then combined and run through a wah, a looper and a delay into a single amp. The amp (Ampeg PF-500) has an onboard single-knob compressor running at about 8 o'clock. Never gave much thought to it.

    Would a single compressor before the amp squish the 'wrong' frequencies? Say I run Clean and Dirt with ambient reverb. The compressor would kick in when the reverb hits the threshold, and squish the whole signal, including the Clean, no?

    Running a separate compressor for each channel would mitigate this, but that seems a tad excessive, not to mention expensive.

    The Synth loop is not very dynamic to begin with, so maybe a compressor would be of little use?

    At the moment I am looking at running separate compressors on the Clean and Dirt loops. Light compression on the Clean, and heavier compression on the Dirt.

    Feel free to unload your compression wisdom on me. Do you compress before or after reverb? What about delay? Does your wah go into the compressor or after?
  2. TraktorBass


    Mar 9, 2017
    After thinking about this, I realized it's not possible to compress only the Clean loop.
  3. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Inactive

    Feb 23, 2011
    How about placing your compressor as the very first thing in your signal chain, before the split happens, so that all 3 paths are fed with a compressed clean signal?

    Personally I have my compressor as the very first thing after my bass, and I make use of some parallel processing as well within my signal chain, and at least for me that works well.
    Last edited: May 23, 2021
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    A single-band compressor will always compress all frequencies, it’s literally just like an automatic volume knob. You can only specify what frequency range you want affected on either a multi band comp or one with a filter in the sidechain.

    The reverb will almost never be what triggers the compression, because its peak levels are typically lower than your regular notes.

    Your best bet here really is to put a comp near the beginning of the chain, before the splitter. Or pick your most peaky dynamic effect, like certain wahs, and put a comp just after that as a limiter.
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  5. TraktorBass


    Mar 9, 2017
    That does seem like the most sensible option, thank you.

    Does the compressor not affect the dynamics of any dirt pedals after it?

    Thanks for chiming in! The wishy washy reverb can get rather loud at times, so a limiter at the end of the dirt chain would rein that in I suppose.
  6. NoiseNinja

    NoiseNinja Experimental-psychedelic-ambient-noise-drone Inactive

    Feb 23, 2011
    No, on the contrary a compressor might limit the dynamic range of dirt effects if the compressor is placed after them, but even then it would depend entirely on which settings you use on the compressor, how I have my compressor set it hardly affects my playing dynamics, it just makes my tone sound more focused and punchy and adds a bit of extra snap and bite to it.

    Edit!: Ah, I think I know what you mean, like acting dynamically to your playing, as in adding more or less dirt depending on your picking dynamics, in that case yes, if the compressor is set like that, but in that case it would limit the dynamic range of your clean playing as well.

    Just set the compression rate sufficiently low and the threshold sufficiently high and you should be good, or get a multi band compressor that allows for parallel compression (as in mixing compressed and uncompressed clean signal), like the TC Electronic SpectraComp that I use.
    Last edited: May 23, 2021
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  7. Wasnex


    Dec 25, 2011

    That's unfortunate. Distortion is going to be accompanied by a certain amount of compression; so it can be helpful to add a similar amount of compression to the clean channel. Without compression on the clean channel, people often say the composite signal sounds like the distortion is riding on a clean signal. When you compress the clean channel, it helps the two signals integrate, so it sounds like a true composite and less like two signals blended. Hopefully that makes sense.

    Compression shouldn't trigger off your reverb, but I believe it will make it sound like the reverb tail is longer than it actually is. Essentially as the note decays, the compressor will open up and increase gain. The increasing gain brings the reverb up in the mix, so it sounds like it takes longer to decay. To avoid this, you typically run compression before effects like reverb and delay.
  8. TraktorBass


    Mar 9, 2017
    Gotcha. Thank you

    Yea, the Signal Blender runs two effect loops plus a clean blend channel (no loop). So no possibility to add compression to only the clean channel.

    Ref. the riding a clean signal, I think I see what you mean.

    An uncompressed clean signal would be ‘all over the place’ in terms of dynamics, while a distorted signal is compressed from being run through dirt boxes?

    I guess a compressor before the Signal Blender would do the trick then.

    Longer reverb tails would not necessarily be a problem for me. I will have to test it out to see how it sounds.

    Thanks for chiming in!

    I have an MXR M87 on the way, and a Boss LMB-3 on my shelf. I’m guessing the M87 would go before the blender, and the LMB-3 would fit nicely at the end of the dirt channel.

    Any thoughts?
  9. AdamR

    AdamR Inactive

    Sep 24, 2007
    Bethel CT
    Ebs multicomp can be set to just compress the lows.
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  10. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    No, it just compresses everything once the threshold is reached. It's frequency agnostic. If the reverb is loud enough to trigger compression means you have way too much reverb :roflmao:

    The most common reason for using multiband compression is that the lowest frequencies will trigger the compressor before the highest ones. So slamming the open B string will suddenly bring down your overall level, unless you compress only the lows. Maybe you want some compression only on the highs so popping doesn't clip the amp. Etc. In recording applications, it's not uncommon to have 3 or more bands of compression to keep levels across the frequency spectrum under tight control.

    Single knob compressors may be just adjusting the threshold, or they might also affect attack/release, ratio, makeup gain. Each one will act differently, so you have to use your ears.

    P.S. If you use a DAW at home, it most likely will have a multiband compressor plugin. Recording your bass and then applying the different factory presets for the compressor during playback will show you how it can be used for tonal shaping.
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  11. vvvmmm


    Dec 6, 2016
    If you want that limited, fine.

    But there's a trick I use I learned from a J. Mascis interview*: put a level control at the end of the chain. A clean boost pedal - any pedal, really, and a turned down overdrive or even a Muff can do this and give you some EQ control - that allows you to lower the volume of the input signal will work, and likely give better dynamics.

    *He reco's that approach to control stacked dirt pedals, and that's how I use it - it works well on modulation, also.
    Last edited: May 23, 2021
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  12. Wasnex


    Dec 25, 2011
    Unfortunately this is a fairly common problem with the various blender pedals I have seen. The setup you are describing sets up the two compressors in series.

    What I am suggesting is put one compressor in parallel with the compression in the distortion channel. Running two compressors in series can definitely be useful, but it won't be the same as compressing the clean loop in parallel with with the distortion loop.

    But IMHO try it.

    One way around this particular problem is to use a pedal that splits the signal into dual mono. I have an old MXR KFK EQ that does this. You could set up two processing channels off the KFK and then blend them back together with something like a Radial Mix-Blender. Of course this type of setup has it's own problems.

    Ideally I guess you need to find a blender pedal with loops for both channels.
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  13. Michedelic

    Michedelic MId-Century Modern

    Perhaps you may want to look at this unit...
    It gives you total control over three separate paths. The interaction between wah and compression is weird and subjective, I prefer comp beforehand.
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  14. Talk to OBNE about having an insert added to your clean blend.
    Circuit-wise, it shouldn't be too difficult to accommodate setting it up for a compressor on the clean channel; it's space constraints within the enclosure that may hamper the idea short of rehousing in a new slightly larger enclosure.

    Also, the cost of shipping it to OBNE, the money for the mod, and the price of return shipping might be prohibitive to the point where grabbing Michedelic's suggestion of EHX Tri-Parallel Mixer is financially preferable...

    Or, have the OBNE Blender modded locally.
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  15. TraktorBass


    Mar 9, 2017
    So I ended up running a single compressor before the Signal Blender. Sounds all right to my ears.

    Now I am GASing for the Tri-Parallel Mixer. Next pedal board revision perhaps..

    Thank you guys for the replies, much appreciated! :)
    Wasnex likes this.