You're very welcome! Yeah we should make clips with other basses, I'll keep it in mind, thanks for the suggestion!
The Grunt switch control the amount of low end going to the main clipping stage (CMOS). This interacts with the Drive knob, so that you can control, how much low end dirt (AKA fuzzyness) you want... it also allows for adding clarity in hotter scenarios, since this pedal has a ton of bass, at full gain, you might want to cut some low end if you don't want the whole room to rumble

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The frequency controls on the B7K are: 100Hz, 1kHz, 2,8kHz and 5kHz. (Low, Mids, Hi-Mids and Treble).
Check the page if you want to dig more info:
Products « Darkglass Electronics I'm here if you have more questions as well

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Regards! -Doug.