Compressor/Limiter-Line Level

Ideal Use Cases

The RDL ST-CL2 is a line-level compressor and limiter designed for audio paths that require positive level protection, smooth gain reduction, and tight peak control. It is suited to systems where signal levels must remain controlled without extensive manual adjustment. Its 10 kΩ balanced input and 150 Ω balanced output may also be connected unbalanced, allowing the module to work with either connection type. An adjustable input signal range of 10 to +4 dBu for 6 dB of gain reduction, along with a +22 dBu maximum input, accommodates a range of line-level signals.

Why Choose This Model

The ST-CL2 combines a very low-noise compressor, multi-stage incremental gain reduction, and an INF:1 peak limiter in one fully automatic design. Its compression ratio automatically adjusts from 1.5:1 to 10:1, while release time adjusts automatically up to 500 ms. This automatic operation reduces setup requirements while maintaining controlled output levels. Yellow and red LEDs provide immediate visual indication of NORMAL and HEAVY compression, helping the operator see how actively the module is managing the signal.

Installation and Integration

The balanced input and output can each be wired for unbalanced operation when required. Output level is adjustable from OFF to +8 dBu, providing control over the level delivered to the next component in the audio path. A stereo COUPLE interconnection is provided for installations that use two channels together. The module requires 24 Vdc at 50 mA through its RDL SupplyFlex power input configuration. Recommended power supplies are the PS-24AS for the USA and PS-24AX for international use; the power supply is not included.

The specified ambient operating range is 0° C to 55° C. Package dimensions are 2 x 2 x 4 inches, with a shipping weight of 0.2 pounds and a WEEE weight of 0.145 pounds. A specification sheet is available in PDF format, while engineering functional block and panel diagram files are listed in American DXF format.

Performance Highlights

Frequency response extends from 10 Hz to 20 kHz within ±0.2 dB over the full compression range. Noise is specified below -78 dB, unweighted, with +4 dBu input and output. Total harmonic distortion is below 0.05% at 1 kHz when operating below the compression threshold. With active gain reduction, distortion remains below 0.1% at 1 kHz with 3 dB of reduction and below 0.15% at 1 kHz with 6 dB of reduction.

Common-mode rejection is greater than 60 dB from 50 to 120 Hz. Attack behavior includes 500 ms averaging compression at a +4 dBu input, with fast compression also specified. The automatically adjusting release time extends up to 500 ms. Together with the automatically variable compression ratio and INF:1 peak limiter, these characteristics provide both gradual level management and firm control of audio peaks.

What Makes It Different

The ST-CL2 is built around fully automatic, multi-stage gain management rather than a collection of manual compressor controls. It combines smooth, intended-to-be-inaudible gain reduction with fast compression and tight peak limiting. The result is a module focused on level protection with minimal setup. Its stereo coupling connection, balanced or unbalanced compatibility, adjustable output, compression-status indicators, and SupplyFlex power configuration support straightforward integration into different line-level signal paths.

Final Assessment

The RDL ST-CL2 offers automatic compression and peak limiting for systems that need controlled line-level audio. Its wide 10 Hz to 20 kHz response, low specified noise, incremental gain reduction, variable compression ratio, INF:1 limiting, and stereo coupling provide a focused combination of protection and signal control. It is a strong match when fully automatic operation, visible compression status, and minimal setup are central requirements.