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Bitwig Key-Track Modulator - Key-Track Modulation Using Note Inputs

Bitwig Guide | Jun 23, 2022

The Key-Track modulator adjusts modulation based on note input, allowing parameters like filter cutoff to follow keyboard note position, with C3 typically as the neutral center. By tweaking the center and spread, you can control how much and how quickly modulation changes as you play higher or lower notes, and the modulation works best on instrument tracks because they support note input. To apply Key-Tracking to audio tracks, a note receiver is needed to route notes from an instrument track, enabling features like key-tracked filters even on pure audio clips.

You can watch the Video on Youtube

Short Overview

I use the Key-Track modulator to map note input from my keyboard to control parameters like filter cutoff, letting higher or lower notes push the modulation up or down. It works by defining a center note where no modulation is applied and spreading modulation values above and below that point, which I can adjust as needed. If I'm working with audio tracks that don't generate notes directly, I route note data in from another instrument track using a note receiver, allowing me to Key-Track effects on any channel. This flexible approach helps me shape sounds and filter responses musically, driven by the notes I play.

Overview of the Key-Track Modulator

In this video, I explain how the Key-Track modulator works in my DAW and how it's fundamentally a node pitch modulator. The Key-Track modulator requires keyboard or note input to function, making it essential for both instrument and audio tracks, depending on how the notes are fed into the device.

How the Key-Track Modulator Operates

The concept is straightforward: the modulator uses a transfer line that maps incoming MIDI notes to modulation values. For example, when I input the note C3, there's no modulation because C3 is set as the center-point, corresponding to zero on the modulation line. If I play higher notes like C4, positive modulation is applied; conversely, pressing a lower note like C2 results in negative modulation. The further up or down the keyboard I play, the greater the modulation effect.

Adjusting the Modulation Curve

There are several options to customize how the modulator responds to notes:

Applying Key-Tracking to a Filter

A key application for the Key-Track modulator is controlling the cutoff frequency of a filter based on incoming MIDI notes. I place the device on an instrument track, and it responds to the note data from a MIDI clip. For example, if I double-click the filter frequency knob, it resets to 262 Hz, which matches C3 by default. This means that C3 is the root note for the Key-Tracking, aligning the zero modulation point.

When I set the modulation amount to match the spread (for example, 64), the modulation is calibrated so that octave jumps correspond to predictable frequency changes. This allows for precise musical tracking. By playing C4 or C1 and observing the filter response, I see the cutoff moves exactly according to the notes I input.

Auditory Demonstration

To illustrate, I can use a noise source and sweep the bandpass filter. With C4 as the center note, increasing the resonance highlights the filter peak exactly at C4 when triggered. Using an EQ, I can visually verify the resonance aligns with the expected note frequency, confirming accurate Key-Tracking.

Integrating with Audio Tracks Using Note Receiver

A key limitation of the Key-Track modulator is it only responds to MIDI notes. Audio tracks typically don't have note data, so directly Key-Tracking on them isn't possible. To solve this, I use a note receiver device to route MIDI notes from an instrument track (where notes are present) to an audio track's effects chain. This allows the filter on the audio track to modulate cutoff based on incoming notes from another track.

Practical Summary

In summary, the Key-Track modulator is a tool that lets me link MIDI note pitch with parameter modulation, commonly used to adjust filter cutoff following the note being played. Great results depend on ensuring the device receives MIDI input, either directly on an instrument track or indirectly by routing note data to an audio effect on an audio track. Fine tuning with spread, center, and mode settings gives me musical flexibility, whether I’m shaping synth sounds or designing creative effects chains for audio clips.

Concept Clarification

Key-Tracking: This term refers to linking a parameter (like filter cutoff or oscillator pitch) to the pitch of the note being played. It’s a fundamental part of synthesizer sound design, frequently used so higher notes open up a filter more than lower notes, for example.

Modulation: In this context, modulation means changing a parameter in real time based on note data or other controllers. The Key-Track modulator automates this process, mapping a range of notes to a range of modulation values.

Note Receiver: This is a utility device in many modern DAWs that allows MIDI or note data from one track to be sent to another, enabling creative routing and advanced modulation techniques.

With these tools and techniques, I can achieve expressive, musically reactive sounds with precision across both MIDI and audio tracks.

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 Key-Track modulator is a node pitch modulator and this one is completely driven by node inputs.
[00:00:06] So you need the keyboard input or node input from somewhere.
[00:00:10] And how this works is pretty simple, actually.
[00:00:14] We have here this transfer line and if you input a node of C3,
[00:00:19] there's no modulation applied because it's exactly the center here, which is zero.
[00:00:24] And if you press a node of C4, for instance, which is here,
[00:00:28] then you can see you apply a bit of positive modulation.
[00:00:32] If you press C2, then you apply a bit of negative modulation.
[00:00:36] So the more you go up or go down the keyboard or your nodes,
[00:00:41] then the more modulation you apply, of course.
[00:00:45] If you want to make this or change this a bit, then you can, of course,
[00:00:49] skew this transfer line here with the spread.
[00:00:53] We can apply more modulation, more faster modulation, the more you go up or down the keyboard, right?
[00:01:00] You can also change the center here of this, so we can zero or maybe bring the zero line to D4 or maybe C4.
[00:01:07] I don't know. It's really up to you, C4.
[00:01:13] So now we have C4 and if you play C4, then, of course, zero modulation is applied.
[00:01:18] And if you go C1, then the same modulation is applied as before when you press C4.
[00:01:23] You can change the center here, but C3 is perfectly fine.
[00:01:28] Also the spread of 64s, most of the times, perfectly fine, is I think it's also the maximum value.
[00:01:34] There's also an absolute mode here, which is kind of the same, but you have more nodes.
[00:01:38] So you can dial in more specific modulation values here for different nodes if you want to do that.
[00:01:45] But I really never use it that much.
[00:01:48] I always go for relative, most of the times, but sometimes maybe you have a new case for this.
[00:01:54] So relative is perfectly fine here.
[00:01:58] And let's close this down and we have this here on a filter device.
[00:02:02] And we want to change the cutoff here, the cutoff frequency with nodes from the node clip, right?
[00:02:10] So we are on our instrument track here, which is really important with the instrument track.
[00:02:15] We want to change the frequency of this here.
[00:02:17] So when you double click this frequency node, you can dial in any frequency you want here, right?
[00:02:24] But if you double click, then it centers or goes back to a specific frequency.
[00:02:29] In this case here, it's 262 hertz.
[00:02:32] And you can see this down below here in the info bar.
[00:02:36] 262, which happens to be the case, is exactly C3.
[00:02:42] We have also here C3 as a center point or the root node.
[00:02:47] And you can now apply here modulation to the frequency.
[00:02:53] And how much you want to apply is really up to you.
[00:02:57] But in this case, if we apply here exactly 64,
[00:03:03] maybe you can dial this in the inspector 64,
[00:03:07] which is exactly the number of the spread here, right?
[00:03:12] You can change where the frequency knob is positioning with your nodes.
[00:03:19] So if we take this node clip here and paint in a node of C3,
[00:03:27] give this a play here, there's no instrument on there, so there's no sound.
[00:03:31] You can see we have the modulation exactly on this line, right?
[00:03:35] So there's no modulation applied.
[00:03:39] If we go here up to maybe C4 and see we have now here,
[00:03:48] we are here on this diagram now, where we apply a bit of,
[00:03:53] I think it's maybe 12 semitones probably in frequencies.
[00:04:01] Up here, this knob.
[00:04:02] So we are probably exactly here with the frequency knob at C4.
[00:04:11] Because we dialed in 64 here exactly in steps, so it matches perfectly.
[00:04:18] So we have basically a Key-Tracked cutoff here.
[00:04:22] We can also use here maybe a band pass and bring in, let's say, a noise.
[00:04:31] Or let's use a stone device where we have here filter frequency.
[00:04:39] And we can go to, let's say, C4.
[00:04:44] It's exactly here where the point is, where our modulation point is.
[00:04:48] But let's go for bring the noise in and bring up here the resonance.
[00:05:00] You can see we have here picking noise at exactly C4.
[00:05:05] And we can check this here with the EQ plus exactly at C4, right?
[00:05:15] So we have a Key-Tracked filter.
[00:05:19] The only problem with this is now that this only works on an instrument track
[00:05:26] because we need notes.
[00:05:28] You need a note input.
[00:05:29] And there's no dropdown menu here where you can import notes from different tracks
[00:05:34] because we have also audio tracks here.
[00:05:37] And you probably want to Key-Track also on an audio track.
[00:05:40] But on an audio track, there's no key input.
[00:05:43] There's no notes.
[00:05:45] Nothing you can play, right?
[00:05:46] There's only audio files on here.
[00:05:49] So when you drag this filter on an audio clip here and we maybe import here a drum loop.
[00:05:57] Maybe something, let's track this audio clip, this one on here.
[00:06:06] And we have this playing.
[00:06:08] And we want to Key-Track to some notes happening on here, on this different track, right?
[00:06:15] So we have this instrument track where there's only a note clip on there.
[00:06:19] And we have this audio track where there's only an audio file on there and this filter.
[00:06:23] So we need to get the notes from this track to this track only to change the Key-Track.
[00:06:30] So you can do this by using a note receiver.
[00:06:34] And you can just import here from the instrument track the notes.
[00:06:40] And now you can just input here different notes.
[00:06:46] And you can see it's changing here the modulation values and also the frequencies of the cutoff
[00:06:57] here from the filter.
[00:07:00] So the main point of this Key-Track modulator is that you need the key input.
[00:07:06] You need the note input.
[00:07:07] Either you get it from a different channel when you use this here on an audio track or
[00:07:12] you use the Key-Track modulator on a device that is on an instrument track where you already
[00:07:17] have notes, for instance, on an instrument itself or on an audio effect on an instrument
[00:07:22] track.
[00:07:22] [BLANK_AUDIO]