DocDerr is Empirical Labs' first compressor in the API 500 format — six sections of digitally controlled analog electronics packed into one module after more than two years of development. A low-noise preamp handles line-level or instrument-level signal, the EQ section offers a high-pass filter and three parametric bands, and the dynamics section combines Empirical Labs-style compression with a circuit emulating analog tape saturation.
A complete channel strip in a single 500 series slot
Instead of building a chain from a separate preamp, EQ, and compressor taking up three slots in a lunchbox rack, DocDerr fits all of it into one module. An internal jumper turns it into an instrument preamp with 16dB of extra gain, ideal for acoustic guitar, bass, or synths plugged in directly. Three parametric bands — LF (80-500Hz), MF (250Hz-4kHz), and HF (3.5-15kHz) — give continuously variable ±14dB control, and pressing the two bottom buttons together narrows the Q on the mid band, making it easier to zero in on a problem frequency on a vocal or guitar.
Parallel compression as the primary way of controlling dynamics
DocDerr deliberately has no separate threshold, ratio, or attack knobs — the compressor runs on fixed, internally set time constants (attack roughly 1ms, release 0.2s) and works as a complex envelope generator that starts musically saturating the signal at heavier gain reduction rather than simply squeezing it. The main control surface is the Mix knob, blending the clean, EQ'd signal with the compressed and saturated version — close drum mics tend to work well around 6-9dB of gain reduction with a 50-60% blend, while room mics often want more reduction and a higher blend to bring out the character of the space. That layout removes the usual wandering through compressor parameters and reduces the decision to one question: how much of the effect should be audible in the mix. The module is stereo linkable, and in an EL500 rack, linking engages with a single button.
KEY FEATURES
- Six sections of digitally controlled analog processing in API 500 format, horizontal orientation
- Low-noise line/instrument preamp with 16dB extra gain via internal jumper
- Four-band EQ: two-position high-pass filter plus three parametric bands
- Narrowable Q on the mid band (simultaneous press of the bottom two buttons)
- Compressor with fixed, internal time constants and musical saturation at heavy reduction
- Tape saturation circuit softening loud highs (filtering plus germanium clipping)
- Mix knob for parallel compression
- Gain-reduction metering on the front panel
- Stereo linking, single-button in an EL500 rack
- Switchable output: single-ended or differential (+6dB)
TECHNICAL SPECIFICATIONS
- EQ section frequency response: 3Hz-180kHz (-3dB points)
- Dynamic range: 120dB (from maximum output at 0.5% THD to minimum output)
- Noise floor with Mix at 0: typically -91dBu
- Distortion at 1kHz: 0.0006% to 10% depending on mode and settings
- Maximum input level before hard clipping: +22dBm (Line In mode)
- Maximum output level (Mix at 0): +28.5dBm
- Compressor time constants: attack approximately 1ms, fixed release 0.2s
- Input impedance: 120k Ohms (Instrument mode), 20k Ohms (balanced Line mode)
- Output impedance: less than 75 Ohms
