The „Isochronic Modulator“ is a Nyquist plug-in for Audacity designed to create isochronic tones by modulating the amplitude of a selected audio track, typically a sine wave, using a low-frequency oscillator. This effect is commonly used for brainwave entrainment, although the author of the plugin does not endorse or claim relevance to such theories. The original plugin, created by Steve Daulton, allows users to control the pulse width (the duration of the „on“ state relative to the „off“ state), fade time (the speed of the transition into and out of silence), and the modulation frequency and depth, which can be ramped from initial to final settings.
An updated version, „IsoMod 2,“ was released in 2014, which added the ability to select different pulse shapes, including sine, triangle, sawtooth, inverse sawtooth, and square waves. This update was significant because it allowed for cleaner isochronic tones with fewer harmonics, particularly when using a sine wave, compared to the original’s reliance on square or rectangular wave shapes. The plugin is available for download from the Audacity community wiki and other sites like AudioNyq. Further modifications have been developed by the community. Elliot Mebane created a set of enhanced plugins based on the original: „IsomodExtended“ increases the maximum modulation frequency to 150 Hz, „IsomodInOut“ allows separate fade-in and fade-out times, and „IsomodEnvelope“ provides traditional envelope controls (attack, decay, sustain, release). These modified versions are available on GitHub and offer greater flexibility for creating specific sound envelopes.
Audacity: Creating Isochronic Tones
https://www.kvraudio.com/product/isochronictones-by-saschart
https://github.com/ElliotMebane/IsochronicToneGenerator/blob/master/
https://forum.audacityteam.org/t/add-waveform-options-to-isochronic-modulator-plug-in/15908/17
https://plugins.audacityteam.org/nyquist-plugins/effect-plugins/modulation-effects