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Message: [QUOTE="Bombastus, post: 91858, member: 2178"] Researchers modeling classic distortion pedals found pre- and post-distortion filters act as separate stages because each position changes a nonlinear circuit differently. Put the filter first, and you change what reaches the clipping stage before any new harmonics are created. A bass cut after distortion can make the finished signal leaner, but the low frequencies have already helped drive the nonlinear stage by then. Move the same cut ahead of the gain, and you change the conditions that create the distortion, which is why two settings with similar final EQ can still feel very different under your fingers. [HEADING=2]Pre-distortion filtering changes what hits the limit[/HEADING] A guitar signal is a stack of fundamentals, harmonics, pick transients, and noise arriving at one nonlinear stage together. When the combined waveform approaches the stage's available swing or clipping threshold, a strong low-frequency component can help push the entire signal into nonlinear behavior sooner. Reduce some bass beforehand, and those low components contribute less to the waveform entering the stage. Higher frequencies can still clip, but the balance of what crosses the nonlinear region changes, often making palm-muted notes feel firmer and chords less congested without simply turning the bass knob down afterward. This is why a pre-gain low cut can seem to alter compression as much as tone. A heavily driven stage flattens peaks and changes the envelope of the signal, so reducing the frequencies that provoke the deepest excursions can leave more contrast between the attack and the body of a note. Post-distortion EQ cannot reverse the process. It can remove low-frequency output, but it cannot restore a transient already flattened by clipping or undo harmonic products generated while the full-band signal was driving the circuit. Boosting the bass afterward can restore spectral weight without forcing the clipping stage to process the same low-frequency amplitude. A lean-looking pre-filter curve can therefore produce a finished tone that still sounds broad, but behaves more cleanly while the nonlinear stage is being driven. [HEADING=2]Intermodulation makes the difference broader than bass[/HEADING] Nonlinear circuits do more than create harmonics above each note. Feed several frequencies into the same nonlinear stage and they can also produce sum and difference components, a process called intermodulation, so changing the spectrum before distortion changes which frequency combinations get a chance to interact. Work on [B][URL='https://dafx.de/paper-archive/2007/Papers/p189.pdf']filter-distortion-filter pedal models[/URL][/B] makes this point in a useful way. The researchers retained even sub-audible frequency behavior in their models because mixing between very low components and audible ones can create products inside the audible band. A low cut before distortion therefore does not merely remove bass that you could add back later with an EQ. It can reduce the low-frequency ingredients feeding those nonlinear combinations, while a later bass boost can restore weight without recreating the same distortion pattern. The difference becomes easier to hear on dense chords and low tunings. Several strong notes arriving together give the nonlinear stage more simultaneous frequency content to mix, so trimming lows before clipping can clean up the midrange even when the final output is later made just as full. [HEADING=2]Filter position changes feel as well as frequency balance[/HEADING] Players often describe this result as tightness, but the useful part of the word is timing. A big low-frequency swing lasts longer than a sharp pick transient, and letting it dominate a clipping stage can keep the circuit in a more heavily nonlinear region through more of the note. Reduce some of that low-end drive and the leading edge can stand apart more clearly from the sustain. The sound may seem faster or more controlled even when a spectrum analyzer shows only a modest difference after you compensate the bass later. Great Eastern FX uses this relationship directly in [B][URL='https://goldmidi.com/community/threads/great-eastern-fx-has-debuted-the-transformer-boost-pedal.77258/']the Transformer Boost low-cut behavior[/URL][/B]. Opening the low end sends more bass into its germanium transistor and output transformer, increasing coloration and saturation, while cutting lows gives the same basic gain structure a cleaner, tighter response. There is no universally correct cutoff for this job because pickups, tuning, gain level, circuit topology, and the next device all change the result. A gentle cut can remove enough low-frequency drive to sharpen the attack, while an aggressive setting can hollow out the instrument before the distortion ever has a chance to build body. The practical dividing line is simple to hear once you know what to listen for. If cutting bass before the gain makes chords separate, attacks recover, and distortion stop swelling around low notes, the filter is controlling the nonlinear stage rather than merely tidying its output. [/QUOTE]

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