TAP-plugins
Tom's Audio Processing plugins
for audio engineering on the Linux platform

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## TAP Chorus/Flanger

This plugin is an implementation capable of creating traditional Chorus and Flanger effects, spiced up a bit to make use of stereo processing. It sounds best on guitar and synth tracks.

### General information

Unique ID | 2159
I/O ports | 2 inputs / 2 outputs
CPU usage (44.1 kHz) | 2.8%
CPU usage (96 kHz) | 6.2%
Hard RT Capable | Yes
In-place operation | Supported
run_adding() function | Provided

### Usage tips

The Chorus and Flanger effects operate on a very similar basis, that's why they were implemented in the same plugin. Both effects are achieved by creating a time-varying delay of the incoming signal and mixing it with the original. The delay time is modulated by a sinusoidal. After the time-varying delay is applied to the signal, it is further delayed by an (adjustable) amount of time. If this additional delay is small (under 10 ms), then mixing the dry and wet signals will introduce strong phase distortions, and thus a Flanger effect is achieved. If the delay time is greater than 20 ms, then the wet signal is more likely perceived as an additional "voice". Thus, mixing the two signals yields a Chorus effect.

The Frequency control determines the LFO frequency with which the time-varying delay is modulated. The higher the frequency, the more intense the effect will be. Values in the range of 1-3 Hz should be a good starting point in most cases.

This plugin is capable of creating true stereo chorus/flanger effects. The L/R Phase Shift control is provided to this end. The two LFO's controlling the delay modulation of the two channels run in sync with the same frequency, but the phase shift between them can be adjusted with this control. The higher this setting, the stronger the "stereo-ness" of the effect will be. When set to 0, processing of the two channels will be in-phase; when set to 180 degrees, the two LFO's are is counter-phase to create the widest stereo effect.

The Depth control allows for adjusting the modulation depth of the delay. Increasing it will result in stronger modulation using the same LFO frequency. It should be noted that the Frequency and Depth settings jointly determine the intensity of the effect. Smaller frequencies usually allow for using a greater modulation depth, and vice versa. If the modulation is fast (higher frequency) and deep (higher depth) at the same time, a vibrato effect is introduced. You may or may not want this.

The Delay control determines the fixed amount of time with which the signal is delayed after the time-varying delay has been applied. The setting of this control distinguishes between the Chorus and Flanger effects. Delays smaller than 10 ms can be labeled Flanger, delays above 20 ms yield Chorus, and delays in the range of 10-20 ms result in a blend between Chorus and Flanger.

Contour is the cutoff frequency of a high-pass filter applied to the now twice-delayed signal. By setting it anywhere above 20 Hz, you can protect the lower frequency spectral content in the original signal from being disturbed by the effect. Set it to somewhere in the range of 100-500 Hz if you feel that your bass tones get smeared or lose definition. Set it to somewhere between 1000-6000 Hz to have a Chorus/Flanger that lets the bulk of the signal through, but changes the sound of the cymbals, higher guitar tones, etc. This results in an interesting effect when applied to mixes.

The Dry Level and Wet Level settings allow for a final tuning of the sound. The strongest effect is achieved if the two settings are about the same. Decreasing one of them (preferably the Wet Level, to mitigate any unwanted side effects) results in a subtler effect.

### Summary of user controls

name | min. value | default value | max. value
--- | --- | --- | ---
Frequency [Hz] | 0 | 1.25 | 5
L/R Phase Shift [deg] | 0 | 90 | 180
Depth [%] | 0 | 75 | 100
Delay [ms] | 0 | 25 | 100
Contour [Hz] | 20 | 100 | 20000
Dry Level [dB] | -90 | 0 | 20
Wet Level [dB] | -90 | 0 | 20

### Notes

Naturally, the two separate delays described above (one modulated and one constant) are realised at once, as a single delay line. This saves you a lot of CPU cycles (...but you are obliged to run other TAP-plugins in those cycles. Just kidding, of course.)

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