The API 550B 500 Series equalizer is a 4-band workhorse based on classic discrete console EQ circuitry. Its musical curves and forward tone have been a standard for drums, vocals, and guitars on thousands of records. API's "Proportional-Q" circuitry gives tighter, laser-like bandwidth with extreme boosts and cuts, and broad strokes when you just need a couple dB here and there. Whether you're just getting into the 500 series, or have a Lunchbox with an empty slot, you owe it to yourself to try out the 550B and see what it brings to your tracking and mixing.