Time-Variant Gray-Box Modeling of a Phaser Pedal

Roope Kiiski, Fabián Esqueda and Vesa Välimäki

Companion page for a paper in the 19th International Conference on Digital Audio Effect (DAFx-16),
Brno, Czech Republic, Sept 5 — 9, 2016


A method to measure the response of a linear time-variant (LTV) audio system is presented. The proposed method uses a series of short chirps generated as the impulse response of several cascaded allpass filters. This test signal can measure the characteristics of an LTV system as a function of time. Results obtained from testing of this method on a guitar phaser pedal are presented. A proof of concept gray-box model of the measured system is produced based on partial knowledge about the internal structure of the pedal and on the spectral analysis of the measured responses. The temporal behavior of the digital model is shown to be very similar to that of the measured device. This demonstrates that it is possible to measure LTV analog audio systems and produce approximate virtual analog models based on these results.

Sound Example

Original guitar recording

Phased signal with LFO siwtch in the OFF position

Phased signal with LFO switch in the ON position

Matlab Files

You can download the files necessary to implement the phaser model as a single zip file by clicking here.