Lil Sister

An underdrive is essentially the opposite of an overdrive or boost. Instead of adding gain and pushing the amp harder, it reduces certain frequencies—particularly the midrange—before the signal reaches the amplifier. This can effectively pull back the frequencies that contribute most to breakup and distortion.

Why would you use one? An underdrive can help you get cleaner, brighter tones from an amp that’s already being pushed into overdrive. Vintage-style, single-channel amps can sound fantastic when driven hard, but simply turning down your guitar’s volume can sometimes make the clean tone darker or less defined.

An underdrive gives you another option: keep the amp pushed into its sweet spot while pulling back the grit and gain, giving you a cleaner, more open sound without losing the character of the amp.