Legendary Passive Filter

HLF-3C Passive High/Low Filter

Red Rock Sound HLF-3C completes the Passive EQ Collection. This plug-in has 12 dB per octave low and high cut filters, providing broad retro-tonal sculpting or bygone-era special effects, without the inconvenience of insertion loss found with the unamplified passive hardware.

You can easily subtract the unnecessary frequencies in any instrument and sub-group so they stay wonderfully musical in the mix.

The original HLF-3C hardware unit is a true passive design; there are no input/output amplifiers and it does not require any external power. As a result, there is an inherent loss of signal level when using the HLF-3C hardware. The RRS HLF-3C plug-in compensates for this inherent signal loss for simplified use in the modern era; it has unity gain upon insertion (there is no insertion loss until one or both of the cut filters is engaged).

Latest Versions

AUv3 version 1.0.1 (Sep 19, 2022)
VST2 version 1.0.1 (Sep 19, 2022)
VST3 version 1.0.1 (Sep 19, 2022)

VST2 version 1.0.0 (Sep 3, 2022)
VST3 version 1.0.0 (Sep 3, 2022)


Support has ended.


The HLF-3C interface is very simple and includes only three controls:

In — This toggle switch is the plug-in bypass control. When in the down position (bypassed), plug-in processing is disabled altogether. The plug-in is engaged with the switch is in the up position. This switch can be used to compare the processed settings to that of the original signal;
Low Cut — This rotary switch specifies the cutoff frequency of the low cut filter. Ten frequencies are available: 50, 80, 100, 150, 250, 500, 750, 1000, 1500 and 2000 CPS;
High Cut — This rotary switch specifies the cutoff frequency of the high cut filter. Ten frequencies are available: 1.5, 2, 3, 4, 5, 6, 8, 10, 12 and 15 KCS.

- Double click — reset to default value;
- Shift — reduce knob/fader sensitivity.