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When running the bass signal through the OD pedal, the signal gets compressed and this adds harmonic overtones and increases the level of highs and mids to the signal.

Q: When people say the distortion will make the low end drop, what do they mean by that? Is it in terms of Amplitude decreasing to the low end signal or decreasing in volume of the low end sound to human ears as mid and high overtones are now louder?

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    The signal ends up containing more highs than lows, so it sounds like the bottom end has been lost.
    – Tim
    Mar 19 '20 at 7:11
  • @Tim Can you pls clarify more on that? Do you mean in terms of low end signal level’s lost or human ear perception? Thank you.
    – user506602
    Mar 19 '20 at 7:18
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    I guess it's not so much a loss of bottom end, but a gain of top, which then makes the sound less bottom heavy. This is a comment rather than an answer, but makes sense to me.
    – Tim
    Mar 19 '20 at 7:54
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    @Tim sometimes when bass is overdriven, the signal is split to low and high bands and only the high band is run through the overdrive. This keeps the low-end clear, but gives the sound overdriven harmonics and compression. If what you're saying was true and overdrive only caused additional highs, then the parallel two-band processing should result in the same thing and would make no sense. The problem must be either that overdrive removes some low frequencies, or that it adds some unwanted low frequencies that make the sound muddy and that the two-band parallel processing does not add. Mar 19 '20 at 9:02
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    @piiperiReinstateMonica - thanks for all that. I've never used overdrive or distortion on bass, in all the years! It stands to reason that when harmonics are amplified due to overdrive, the higher end of the spectrum will be more pronounced, as harmonics are higher pitch anyhow, and it also makes sense not to amplify the lower end any more - too muddy. The start of any note played will generally be a quick attack, whatever overdrive is doing, and the end will be whenever the player decides it will be, usually. Notes aren't often longer than a bar (not when I play...).
    – Tim
    Mar 19 '20 at 9:19
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When designing overdrive and distortion pedals, the engineers will often include a high pass filter. The sound of a guitar (or bass) has more energy at the lower frequencies. Including this low frequency content in the input to the distortion stage can sound muddy. Source: this analysis of the TubeScreamer pedal https://www.electrosmash.com/tube-screamer-analysis#clip-high-pass

Depending on which OD pedal you have, you could google for the schematic and see if anyone comments on the design. Otherwise try to find a pedal or patch which is specifically designed for bass.

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