HiLoFilter

HiLoFilter is a simple hipass and lopass filter which can be easily controlled with a single knob. It is loosely inspired by the same type of filter found on some Pioneer DJM mixers, and also the The Pilgrim, another great plugin which provides roughly the same functionality.

So for those who haven’t used such a filter, here’s how it works:

  • When the knob is in the center position, no audio processing is performed
  • Turning the knob to the right from center will start to cut low frequencies
  • Turning the knob to the lift will cut the high frequencies

Features

  • Configurable “dead zone” determines how big the middle position of the knob should be. Without a dead zone, filtering will be performed unless the knob is at the exact center. Many users have controllers without sticky points in the center, and during a performance that “close enough” factor ensures that the cleanest possible sound is given without accidentally cutting a bit from the high/low end.
  • Configurable, independent high/low limits for the filter. Sometimes you want the filter to cut 100% of the sound at each end, sometimes not. HiLoFilter has got you covered.
  • Each filter’s range can be independently configured from 20Hz-20kHz
  • Logarithmic scaling for frequency parameters. This ensures that filtering on both the high and low ends of the frequency spectrum is accurate and sane.
  • Filter resonance. Enough said.
  • Great CPU performance, uses nearly 50% as much power as The Pilgrim (more on that below).
  • Dead zone goes up to 11. Rock on!

Performance

Part of the reason I wrote HiLoFilter was that The Pilgrim’s performance was starting to impact my DJ setup. I was constructing a loop mixing set with Ableton Live, where I had 2 “decks”, each with 8 independent channels. To save knobs, I wanted one filter per channel, so I started looking for a nice DJM-like filter. I found The Pilgrim and was quite happy with it, but lacking a dead zone, I built an audio effect rack with a utility plugin (passthru) and two instances of The Pilgrim. The result was a liveset with 2 * 8 * 2 = 32 instances.

A single instance of The Pilgrim uses nearly no CPU, but 32 of them takes a noticeable chunk. I started experiencing audio dropouts from this and all the other stuff in my liveset, and got rid of the effect chain, which reduced the liveset to 16 instances. It was better, but still too high.

HiLoFilter isn’t anything special. I coded it in an afternoon, and the filter code is from the long-retired Convolver plugin from Teragon Audio. But written in highly optimized C++, the performance is almost twice as good as The Pilgrim.

I benchmarked HiLoFilter against The Pilgrim in an empty liveset with 100 instances (more details on the test setup below). The resulting CPU usage reported by Ableton Live was roughly 31% for 100 instances of HiLoFilter, and 58% for 100 instances of The Pilgrim, a CPU savings of nearly 50%.

As HiLoFilter has a passthru dead zone, I benchmarked HiLoFilter both in the passthru state and when filtering and found that the difference was negligible.

The Verdict

The Pilgrim is a great plugin, and I can definitely recommend that users try both it and HiLoFilter to determine which one they prefer more, based on the sound and features. For my needs, a dead zone and low CPU usage were enough to necessitate writing this plugin, but in a situation where one wants only one such plugin on the master channel controlled by a sticky knob, these might not matter.

Limitations

Currently HiLoFilter is only available as a 32-bit Universal Binary for Mac OSX. It should run as both a VST2 and AudioUnit plugin. The plugin should also build under Windows as a 32-bit VST2 plugin (and there are project files ready to do just that), but I’m too lazy too install VS2010 and test under this platform. If someone out there is so willing, grab the source on GitHub and send me a built DLL, which I would be happy to post on my website.

Bugs and Feedback

HiLoFilter was, as mentioned, coded in a short amount of time. It has not been heavily tested, though the filter code was recycled from a more well-tested plugin. You might very well find bugs, so beware! If you do find any, please contact me at support (a) teragonaudio (dot) com. Likewise, if you’re into GitHub, you can file a bug report there.

Licensing

HiLoFilter is licensed under the GPL. It uses the excellent Juce framework, and therefore is also GPL’d. The source code is available at the HiLoFilter GitHub website.

Testing Configuration

Both plugins were tested in an empty liveset, processing an unwarped MP3 playing through 20 audio effect chain containing 5 instances each. My computer is a MacBook Pro 2x2.66 Core 2 Duo with 8Gb RAM and an Intel 310 SSD (3Gbps), running OSX 10.6.8. The test was performed with Ableton Live 8.3 with a buffer size of 512. Your results may vary.


Changelog:

Version 1.0.2:

  • Parameters are correctly saved/restored

Version 1.0.1:

  • Add windows build
  • Improve documentation

Version 1.0.0: (No comment)