SPL IRON mastering compressor, red

Input & Output

Input and output levels are switchable in a control range of +/- 12dB. An increase of the input level leads to more intensive compression. When mastering full scale material, the reduction can be useful. The output is used to adjust the level ratios of input and output.

Attack & Release

The time parameters Attack and Release are switchable in six steps from Slow to Fast. The times vary depending on the rectifier circuit selected.

Side Chain EQs

With the side chain EQs, compression can be focused on frequency ranges. In addition to an inserted EQ, there are four internal EQ presets with a partly complex frequency response.

Rectifier

The tube stage is controlled by a rectifier circuit. There are six diode control characteristics generated by germanium, silicon and LED diodes or combinations thereof.

Variable-Bias Limiter/Compressor

The IRON Mastering Compressor is a variable-bias (variable µ) limiter/compressor from the basic concept.

IRON works on the principle of the bias controlled remote cutoff tube. Parallel to this, a medium-variable-bias triode (sharp-cutoff tube) with a steeper characteristic is connected. The tube bias voltage (BIAS) can be adjusted in three steps.

The tubes are integrated into special Lundahl manufactured balanced high-level double core mu-metal-iron transformers.

AirBass & Tape Roll-Off

The compressor is followed by a passive filter network with two equalizer presets: AirBass and Tape Roll-off.

The AirBass filter boosts low and high frequencies by about 1.5 dB and the Tape Roll-Off filter emulates the typical frequency response of a tape machine.

Link

All functions can be set via switches and the threshold via a rasterized potentiometer which makes recall easy.

The settings of Threshold, Bias, Attack, Release, Rectifier and Side-Chain-EQs are transferred from the right side (channel 2) to the left side in Link Mode, in which the compressor operates with summed control signals.

Auto-Bypass

Channels 1 and 2 are activated with the large illuminated IDEC switches.

In Auto Bypass mode, the channels are automatically switched on and off, which leads to a more objective assessment.

The Interval control is used to adjust the time window continuously between two and 20 seconds.