How PolyIblit Uses Band-Limited Impulse Trains to Deliver Zero-Aliasing Synth Sounds

PolyIblit, a classic freeware virtual analog software synthesizer designed by Andreas Ersson, achieves its highly acclaimed “zero-aliasing” or low-aliasing sound by utilizing Band-Limited Impulse Train (BLIT) synthesis instead of generating raw digital shapes.

In digital audio, classic synthesizer waveforms like sawtooth and square waves contain sharp edges and instantaneous transitions. Mathematically, these sharp geometric corners require an infinite series of harmonics. If you generate these shapes naively in a digital environment, any harmonics that exceed half of your sampling rate (the Nyquist frequency) will fold back into the audible spectrum. This creates harsh, dissonant, and metallic digital artifacts known as aliasing.

PolyIblit bypasses this problem completely by using the BLIT method to construct waveforms from the ground up without any high-frequency data. 1. The Mathematical Foundation: Starting with an Impulse

Instead of attempting to draw a geometric sawtooth or square wave directly, PolyIblit views these waveforms through the lens of calculus. In analog electronics and signal theory: Alias-Free Digital Synthesis of Classic Analog Waveforms