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Bitwig Audio-Rate Modulator - Use raw Audio for Signals

Bitwig Guide | Apr 20, 2022

The Audio-Rate modulator in Bitwig Studio lets you use an audio signal, such as the output from a polysynth or any other track, to modulate parameters like filter cutoff, offering unique sound-shaping options. It provides features like channel selection, gain adjustment, low-pass filtering, rectification, and sidechain input, allowing for creative cross-modulation and feedback loops within or across tracks. By routing audio through effects and back into the modulator, you can generate complex and evolving sounds through self-modulation and extended feedback chains.

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Short Overview

I use the Audio-Rate modulator in Bitwig Studio by routing the audio from my polysynth into the device and then modulating parameters like the filter cutoff with the actual audio signal. The modulator lets me choose different channel sources, adjust gain, filter the signal, and even rectify it for unique effects. I can modulate not only from different tracks but also from within the same track, creating fascinating feedback loops by feeding the processed audio back into itself. This setup opens up a lot of creative possibilities for shaping and evolving sounds in real time.

Overview of the Audio-Rate Modulator in Bitwig Studio

In this video, I demonstrate how to utilize the Audio-Rate modulator within Bitwig Studio, walking through its setup, features, and creative uses. My goal is to show how audio signals can be repurposed for dynamic and intricate modulation of device parameters, resulting in richer and more interesting sound design possibilities.

Routing Audio into the Audio-Rate Modulator

The basic setup begins with a polysynth playing three notes, generating an audio stream. I route this audio output directly into the Audio-Rate modulator. The central idea is that we can use this constantly-shifting audio waveform to modulate any target parameter, most commonly, something like the cutoff knob of a filter. By using the actual waveform of the polysynth output as a modulator, the resulting effect on the sound can become highly expressive and unique.

Modulator Features and Audio Processing Options

Inside the Audio-Rate modulator, several powerful options refine how the incoming audio is processed before being used for modulation:

Channel Select

I can choose which part of the stereo signal to use as the modulation source:

Gain Control

If the polysynth output or audio material is too weak or too strong, I can adjust the gain. This essentially acts as a simple amplifier, allowing precise control over the modulation depth generated from the incoming audio stream.

Low Pass Filter

The low pass filter feature allows me to smooth out or attenuate high-frequency content in the audio stream. This can prevent harsh or overly busy modulation, controlling how aggressively rapid changes in the audio waveform influence the modulation target.

Sidechain Input

Instead of modulating with the same device’s audio, the modulator can pull audio from any other track or source within the project. This makes for extremely flexible routing, such as grabbing a drum track, a VST, or a different instrument and using that as a modulator source. This cross-modulation dramatically expands creative possibilities, enabling modulation relationships across different instruments and tracks.

Rectify Function and Signal Polarity

A key feature is the Rectify button. Normally, audio signals are bipolar, swinging above and below zero. When Rectify is enabled, all negative values are flipped to positive, making the signal unipolar. This is useful for certain types of modulation effects where only positive values are desirable, and it changes the modulation character significantly.

Internal Feedback Routing and Self-Modulation

One advanced technique I illustrate is placing the Audio-Rate modulator directly on the polysynth track itself and routing its input to receive the output of the same polysynth. This creates a feedback loop, where the sound generated by the synth modulates a parameter that in turn changes the sound, which then continues to modulate itself. Such feedback routing can yield complex, dynamic, and sometimes unpredictable sonic results.

Modulating with Effect Chains and Advanced Routing

Bitwig’s modular routing allows me to get even more experimental. For instance, by inserting effects like a limiter or reverb after the polysynth and configuring the modulator to receive its input from anywhere in this effect chain, such as after the limiter or the reverb, I can shape the modulation signal with audio effects as well. This can lead to lengthy and evolving feedback loops, further enhancing the complexity and texture of the sound.

Summary of Creative Possibilities

Further Explanation: Audio-Rate Modulation and Feedback

Audio-Rate Modulation refers to using a rapidly changing audio signal, such as the output of a synthesizer, drum machine, or audio sample, to modulate a parameter (like a filter cutoff) at speeds much higher than typical LFOs (Low-Frequency Oscillators). Because it operates at the speed of audio, the resulting changes are much quicker and often impart complex, textured, or even audio-rate sidebands and artifacts, giving a distinct, organic quality not achievable through slower modulators.

Feedback Loops in Modulation occur when the output of a device is routed back in as a modulator for itself (directly or after going through effects). This setup can lead to self-oscillation or chaotic behaviors, frequently used for experimental sound design. Care should be taken with feedback to avoid undesired clipping or runaway gain.

Through these approaches, Bitwig Studio’s Audio-Rate modulator opens up advanced, experimental methods for sound manipulation and modulation, supporting both subtle enhancements and wild, groundbreaking textures in music production.

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] So the Audio-Rate modulator, you can add this here to the filter device.
[00:00:07] So the setup is basically I'm playing here three notes for the polysynth.
[00:00:15] And the polysynth, of course, creates audio, an audio stream.
[00:00:19] And this audio stream then goes into the Audio-Rate modulator, as you can see on the visuals.
[00:00:27] And then we can apply this Audio-Rate, or this wave, stream of wave, wave forms to some modulation target.
[00:00:39] In this case here, I'm using the cutoff knob.
[00:00:49] So it's basically modulating this cutoff here with the wave form of the audio coming out of the polysynth,
[00:00:59] which makes it sometimes pretty interesting, pretty interesting sound.
[00:01:04] And inside this Audio-Rate here, we have certain features we can use so we can only get the stream of the left channel, the right channel,
[00:01:13] the mid channel, which is the mono signal, or the side channel, which is only the difference between the left and right channel.
[00:01:19] And we can of course add a gain to the audio if we have actually low gain here on the output of the polysynth or if your audio material gets a bit more gain here, it's basically an amplifier.
[00:01:39] And we can apply here a low pass, so if we have actually a lot of high top end content in the audio stream, we can filter this here a bit out, or smooth actually the signal a bit more.
[00:02:02] We have also here a side chain input, which means we can actually grab the audio from a different channel, we don't need to use the audio from coming here from the polysynth.
[00:02:13] So if we have for instance here a second audio track like this one here, and we have an audio file on here that's currently playing, or we have a synth there or some BST, it doesn't matter.
[00:02:26] So we can actually choose here a second channel, grab the audio from there, instead of from in front of the device here.
[00:02:36] So this is also highly interesting to modulate from different sources, from different channels, cross modulate between different tracks, and apply to your current track.
[00:02:48] Then we have the rectify button here, which basically means that it uses the negative values of the audio signal, as you can see here, we have something above zero and something below zero, so we have a bipolar signal.
[00:03:12] And when we put rectify on, you can see we have only positive values, so it maps basically the negative values to the positive range, so it flips it over, so the negative values become positive values.
[00:03:32] To switch this off, you can see we have now bipolar signal here coming in plus and minus values, and rectify switches everything that's negative back to positive.
[00:03:51] Another interesting thing you can do in BitBigStudio is to, let's remove here the filter and put this Audio-Rate on the polysynth itself.
[00:04:05] You can choose here with the device input, not only different tracks, you can also choose the same track.
[00:04:12] So for instance, we have here the polysynth, which is currently the track we are on, right? It's the same track here, or the same synth, and we can choose the output of the polysynth itself and feed the audio signal back into the Audio-Rate modulator and modulate something inside the polysynth.
[00:04:31] So we have kind of a feedback loop, right? So what goes out of the polysynth goes back into the Audio-Rate, modulates something, and then it changes the sound and the sound goes back out and back into the Audio-Rate.
[00:04:44] So this leads sometimes to interesting results.
[00:04:47] [Music]
[00:05:03] You can with the Audio-Rate modulator not only cross modulate between different tracks, you can also modulate from within the same track and modulate the input so you get a feedback loop with the Audio-Rate.
[00:05:15] And you can also not only choose the output of the polysynth itself, you can also do here some kind of effects in the chain. So we have a limiter here, maybe we also use a reverb. That's a bit longer.
[00:05:33] And then you can choose here, polysynth, and then you can choose the peak limiter output, which is back here, right? So you can create a whole chain of effects and change the sound and then feed it back into the front of your chain and create a super long feedback loop.
[00:05:53] [Music]