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
MacOS:
AAX version 1.5.1 (Feb 4, 2026)
AU version 1.5.1 (Feb 4, 2026)
VST2 version 1.5.1 (Feb 4, 2026)
VST3 version 1.5.1 (Feb 4, 2026)
Windows:
AAX version 1.5.1 (Feb 0, 2026)
VST2 version 1.5.1 (Feb 0, 2026)
VST3 version 1.5.1 (Feb 0, 2026)
FILTERS SECTION
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.
The midrange MEQ-5, Passive Filter HLF-3C and the broadband EQP-1A together comprise a full range vintage EQ chain.
BOTTOM SETTINGS PANEL
Undo/Redo
Undo and Redo functions allow undo and redo of changes made to the plug-in parameters.
A/B
A/B buttons allows you to load two independent settings and compare them quickly.
Preset Display
Factory presets are included in the plug-in installation, installed in the following locations:
Mac: Users\[user name]\Music\Red Rock Sound\RRS HLF-3C\Patches
Windows: C:\Users\[user name]\Documents\Red Rock Sound\RRS HLF-3C
You can save the current settings as the Default preset. - Full Reset – is the default preset
Load
Load button allows loading of presets not stored in the locations described above.
Save
Save button allows for save of user presets.
Oversampling
OS x_ activates 2x, 4x or 8x oversampling, 1x disables oversampling.
(note that when the HQ mode is on, CPU will be loaded more than usual).
HQ mode (HQ)
HQ mode is for oversampling, it adds a higher order antialiasing filter. It improves processing quality, but also leads to an increase of the CPU load.
Global Preferences
Button opens Global Preferences menu.
D3D / OGL / CPU (Windows)
This switch allows you to choose between GUI rendering engine:
Normally, no need in switching rendering mode manually, plug-in try to initialize D3D9 then OGL (if D3D9 failed) and CPU (if OGL failed) automatically. But if you have problems with the GUI, you can manually switch and test different rendering methods at work.
This switch is available only in the Windows version of the plugin. For the Mac version, this is not necessary.
Note: Drivers of some video cards (for example, Intel Arc A380) in D3D mode adversely affect the plug-in (periodic noise or whistle), if you encounter a similar phenomenon, use OGL or CPU.
SIMD optimization
This switch enables or disables SIMD optimization, it can be used by multichannel processing with high oversampling. It is undesirable to use in mono and stereo modes, SIMD only slows down the plug-in due to the overhead of splitting the data for optimization.
(Currently in beta testing)
SIMD MacOS
- In the ARM version, you can enable or disable NEON; - In the Intel version, you can enable or disable SSE2.
SIMD Windows
- In the Intel version, you can enable or disable AVX (if supported), or SSE2.
The Windows version has a limitation: if the CPU does not support FMA, then the optimization will not work, even if AVX or SSE2 is supported.
Note: Enabling/disabling SIMD is saved in the project for each plugin individually. i.e. if a specific instance of the plugin slows down, then you can enable SIMD for it, and others, if they are in the project, will not be affected by this optimization.
System requirements
All Red Rock Sound products require a computer with appropriate DAW host software (none of which are included).
Plug-in Activation requires Internet connection!
You can go offline as soon as plug-in is successfully activated.
Versions from 1.0.0 and newer of the Red Rock Sound plug-ins have the following minimum requirements:
Mac OS X 10.14.6 or higher for AU.
Mac OS X 10.14.6 or higher for VST.
Mac OS X 10.14.6 or higher for AAX. Latest version of iLok license manager.
Windows 7 or higher (Windows XP not tested).
Mac: Intel Core i3 / i5 / i7 / Xeon / Full Apple silicon support (M1 or higher).
Windows: Intel Core i3 / i5 / i7 / Xeon / AMD Quad-Core or newer.
In theory, any AAX, VST, VST3, AUv3 compatible host application should work. However, due to plug-in host differences between DAWs - and our own rigorous testing standards - we only officially test our plug-ins and instruments in the most recent versions of Pro Tools, Logic Pro, Cubase, Ableton Live, Studio One, Reaper, and Bitwig. Red Rock Sound plugins are not tested in non-listed systems, but they most likely work as long as the system requirements are met. We cannot guarantee a solution for issues in unsupported systems.