Schroeder Allpass Sections

• Typically, $g=0.7$
• Delay-line lengths $M_i$ mutually prime, and
  span successive orders of magnitude
  e.g., $1051,337,113$
• Allpass filters in series are allpass
• Each allpass expands each nonzero input sample from the previous stage into an entire infinite allpass impulse response
• Allpass sections may be called ``impulse expanders'', ``impulse diffusers'' or simply ``diffusers''
• NOT a physical model of diffuse reflection, but
  single reflections are expanded into many reflections,
  which is qualitatively what is desired.