The Focusrite Blue 315 Isometric EQ is part of Focusrite’s Blue Range world-class analog mastering range of products. The Blue 315 is a 4-band parametric equilizer, with an option for shelving in the 1st and 4th bands. Like other Blue Range products, the 315 does not feature transformers, since all transformers introduce a slight coloration in the signal path that is usually not desired at the mastering stage.

There are two channels of 4-band EQ circuitry - two fully parametric mid bands and two fully parametric bands for low and high frequencies which can also be switched to shelving mode. The bass end EQ stage can also operate over an extended frequency range for very low end control for film or dance music applications. Additional high and low pass filters are included for out of band correctional EQ work.

All EQ stages are based on circuit topologies employed in the Focusrite Studio Console with the added sensitivity, accuracy and control required for mastering applications. The extremely broad frequency response of the Blue 315 - from 5Hz to 140kHz, guarantees smooth frequency and phase response across the much narrower range of human hearing.

Large control knobs on the Blue 315’s clearly laid out facia allow easy adjustment of the switches controls and make it simple to check EQ settings at a glance. The four fully parametric bands feature wide, overlapping frequency ranges. Each offers switching between two frequency ranges, allowing precise frequency selection via rotary switches across the full bandwidth.

Q is variable over an unusually wide range of 0.4 to 2.4, in 11 discrete steps, with the cut/boost control designed to offer finer control around the null point with larger steps at the extremities.

Precise I/P level control is assured with three separate gain controls for each channel - rotary switches for coarse and fine gain control and a continuously variable trim control.

Thanks to buffering between sections, all EQ bands operate independently and are not affected by any of the other bands.

Input sensitivity: -18.5dBu to +13.5dBu
Input impedance: 10kΩ
Frequency response: <10Hz to 65kHz (EQ in, set flat)
(-0.5dB points passively limited) <10Hz to
200kHz (-3dB points passively limited)
Noise: Better than -89dB below +4dBu output level
Distortion: 0.001% THD+N @10dBu, 1kHz
0.003% THD+N @10dBu, 10kHz
Output: +26dBm with 600Ω load balanced and floating
CMRR: -75dB @ 50Hz

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