Ayre QB9 Twenty Upgrade

Ayre implements the filters in a Xilinx FPGA, which provides the necessary horsepower. In an e-mail, Hansen told me that, during the development of Ayre's digital products, "We have custom filters whereby we can load whatever coefficients we want into [the FPGA] . . . an external switch allows us to load different filter coefficients and hear the audible changes they make. This is a great test, as it allows for everything else to be held completely constant. I spent four solid months doing nothing but listen[ing] to the effects of various filters—corner frequency, stop-band response, minimum-phase vs linear-phase, apodizing, sharpness at the 'knee,' windowing functions, interpolation rates (eg, 2x vs 4x vs 8x vs 16x), dithering functions . . . every single factor I could think of.