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Bitwig Comb-Filter Device - Physical Modeling and Metallic Sounds

Bitwig Guide | Nov 18, 2022

The Comb-Filter in Bitwig Studio is a visual comb filter with flexible frequency and feedback controls that can add metallic physicality to synth sounds, making them resemble real instruments like a kalimba or guitar. Unlike other devices, it lacks automatic gain compensation, so users should use a limiter to avoid clipping, and its mix knob allows blending the dry signal. While key tracking can be tricky due to logarithmic scaling, using the Comb-Filter within Bitwig’s FX grid simplifies this by allowing direct frequency-to-key mapping.

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Short Overview

I like using the Comb-Filter in Bitwig Studio when I want to add a sense of physicality or metallic character to my sounds, especially on synths or noise bursts. By adjusting the resonance and frequency controls, I can shape the tone to sound like plucked metal or model the body of an instrument. The blend control lets me mix in just the right amount of dry signal, and I’m careful not to overdo the feedback to avoid unwanted distortion. For key tracking, I find it easier to use the FX grid version, as it follows pitch changes automatically, making creative sound design much more straightforward.

Introduction to the Comb-Filter in Bitwig Studio

In this walkthrough, I am exploring the Comb-Filter device inside Bitwig Studio and demonstrating its unique characteristics, controls, and musical applications. The Comb-Filter is a visual comb filter equipped with bipolar feedback and blend controls, making it a versatile tool for sound design and physical modeling.

Interface and Controls Overview

Frequency Control

With this knob or parameter, I can smoothly select a resonating frequency within a wide range, from 20 Hz up to 3.5 kHz. This gives granular control over where the main resonance or spectral character will sit.

Feedback Knob

The feedback control allows me to set the amount of signal fed back into the filter. Unlike some other devices, such as the Ableton Live Resonator, the Comb-Filter does not feature automatic gain compensation. This omission means I need to be cautious: high feedback can easily result in excessive levels, causing peaking or distortion. For safety, it is wise to place a peak limiter or clipping device after the Comb-Filter.

Mix (Blend) Control

The mix knob lets me blend between the processed (wet) and unprocessed (dry) signal. This flexibility enables subtle enhancements or bold, transformative effects, depending on the context and desired outcome.

Creative Uses and Sound Design Techniques

Adding Physicality and Resonance

One of the standout uses for the Comb-Filter is introducing a sense of physicality or "body" to electronic sounds, such as synths. When applied to a simple synth sound, dialing in resonance around a frequency (for example, around 600 Hz) and adjusting feedback can make a tone sound metallic or percussive, reminiscent of instruments like a kalimba with metallic plucks. This effect works by introducing static resonant frequencies, which do not change with pitch, evoking the fixed formants found in real acoustic bodies.

Exploring Guitar-Like or Percussive Textures

By fine-tuning the resonance and frequency, I can morph synth tones or noise bursts into textures reminiscent of guitars or other plucked string instruments. The filter's static partials mimic the resonant body of real-world instruments, making the Comb-Filter ideal for physical modeling and imitative synthesis.

Tips and Cautions

Preventing Excessive Peaks

Since the Comb-Filter allows for substantial feedback without a built-in limiter, I need to be careful not to drive the feedback too high. Overdoing feedback can lead to harsh clipping or even damage speakers. Using a limiter or clipping device post-filter ensures safer usage.

Key Tracking and Logarithmic Frequency Mapping

Mapping Frequency to Keys

For more advanced setups, such as pitch-following effects, I might want the filter's frequency to track MIDI notes (key tracking). While the built-in CompDevice in Bitwig Studio does not natively support direct key tracking (and setting this up manually involves non-intuitive logarithmic mapping), Bitwig's FX Grid offers a solution.

Using the FX Grid for Key Tracking

Inside the FX Grid, I can insert the Comb-Filter as a module, and key tracking becomes straightforward. By double-clicking the frequency for reference (e.g., matching C3 in Bitwig), I can set resonance and feedback, and now, filter frequency will move in tandem with the keys I play. This approach simplifies mapping and allows for more musically relevant filter behavior.

What Is a Comb Filter?

Explanation of the Concept

A comb filter is named for its frequency response, which features a series of evenly spaced notches or peaks, giving it a visual resemblance to the teeth of a comb. This pattern results from mixing a signal with a delayed version of itself, and the delay time (or phase relationship) determines the frequency and spacing of resonances. Comb filters are fundamental in audio for creating effects like flanging, resonating body simulations, and certain types of reverb.

Conclusion: Why Use the Comb-Filter?

In summary, the Comb-Filter in Bitwig Studio is a powerful tool for introducing metallic formants, body resonance, and vivid physical modeling to any sound source. Its user-friendly controls, combined with the deeper customization possible in Bitwig’s FX Grid, make it suitable for everything from subtle enhancements to radical timbral transformations. With careful adjustment and attention to output level, it becomes an expressive component in any sound designer’s toolkit.

Full Video Transcription

This is what im talking about in this video. The text is transcribed by Whisper, so it might not be perfect. If you find any mistakes, please let me know.
You can also click on the timestamps to jump to the right part of the video, which should be helpful.

Click to expand Transcription

[00:00:00] This is the Comb-Filter of Betwick Studio.
[00:00:03] It's a visual Comb-Filter with bipolar feedback and blend controls.
[00:00:06] And you have your usual controls here.
[00:00:09] You can change the resonating frequency here freely from 20 hertz up to 3.5 kilohertz.
[00:00:16] You can also increase the feedback here.
[00:00:19] And this is the big difference to an Arbus device where you have like a gain compensation.
[00:00:25] Here you don't.
[00:00:26] So you can overdo this.
[00:00:29] So make sure you have maybe a peak limiter at the end here or some clipping device.
[00:00:33] And there's also a mix knob here where you can blend in the dry signal if you want to.
[00:00:40] So how do you use it and why do we want to use it?
[00:00:44] It's probably the next question.
[00:00:47] So when we have some kind of synth sound, maybe bring this out.
[00:00:54] There's something like this, right?
[00:00:59] You can use the Comb-Filter to bring in some kind of physicality to the sound.
[00:01:03] So it sounds like a real body or a real physical device you are playing, right?
[00:01:09] So you use the Comb-Filter here and maybe use here something around 600 hertz, a bit of
[00:01:14] resonance here or feedback.
[00:01:18] And you can hear the synth sound has some kind of metallic feel to it and sounds almost
[00:01:30] like a kalimba or something like this, where you have metallic plucks on there.
[00:01:39] And because the frequency doesn't change when you change the key, it sounds almost like
[00:01:45] real static frequencies or formants of this device.
[00:01:50] So it's a perfect device for physical modeling to bring in some physicality or some physical
[00:02:01] properties to a sound.
[00:02:04] This sounds like a guitar.
[00:02:10] So don't overdo this here.
[00:02:21] So perfectly for that.
[00:02:23] Then you can also do something like using a noise burst and then use just a high resonance
[00:02:37] or high feedback setting to create some sounds with it.
[00:02:48] And you probably want to map this here to a key, the frequency to key.
[00:02:52] And yes, you can add the key track here.
[00:02:57] But I think this one here is kind of logarithmic.
[00:03:02] How you map basically the keys to the frequencies is not easy to do.
[00:03:07] So you need some kind of logarithmic conversion.
[00:03:10] But you don't need to do that, actually.
[00:03:12] You can use the grid for that.
[00:03:15] So instead of using the CompDevice, you just use an FX grid.
[00:03:20] You search for the Comb-Filter and just use that.
[00:03:26] Because here you have already key tracking implemented, all you have to do is maybe double
[00:03:31] click here on the frequency so it matches C3 inside Bitwig Studio.
[00:03:36] You can increase here the frequency or the resonance.
[00:03:41] And then when you change keys, the frequency here changes with the key.
[00:03:48] So you don't need to hassle around with adding a key track modulator to the CompDevice.
[00:03:55] And the Comb-Filter is called Comb-Filter because of the structure.
[00:04:01] You have these evenly spaced out notches here in the frequency spectrum or response.
[00:04:10] So that's why it's called Comb-Filter.
[00:04:13] [BLANK_AUDIO]